SCH4U U3 Thermochemistry & Kinetics

1. What is heat?

a.	A measure of the average kinetic energy of entities in a substance.
b.	The total amount of kinetic and potential energy in a substance.
c.	The transfer of thermal energy from a warm object to a cooler object.
d.	None of the above.

c.	The transfer of thermal energy from a warm object to a cooler object.

2. A chemical system in which neither energy nor matter can flow into or out of a system is described as

a.	a closed system.	c.	an isolated system.
b.	an open system.	d.	a chemical system.

c.	an isolated system.

3. The change in energy of a system (ΔE_sys) is often described  by the term q (heat), but this assumes that 

i.  the temperature of the system is 0^oC.

ii.  the work done in the system is zero.

iii.  the molar enthalpy of the system does not change.

iv.  the volume of the system does not change.

a.	i. only	d.	both i. and ii.
b.	ii. only	e.	both ii. and iv.
c.	iii. only

d.	both i. and ii.

i.  the temperature of the system is 0^oC.

ii.  the work done in the system is zero.

4. The specific heat capacity of a substance is

a.	the quantity of heat required to raise the temperature of one mole of a substance by 1o Celsius or Kelvin.
b.	the quantity of heat required to raise the temperature of one gram of a substance by 1o Celsius or Kelvin.
c.	the quantity of heat required to raise the temperature of one molecule of a substance by 1o C or K.
d.	the quantity of heat required to raise the temperature of a substance by 1o Celsius or Kelvin.

b.	the quantity of heat required to raise the temperature of one gram of a substance by 1o Celsius or Kelvin.

5. To conduct an experiment, a scientist places a small piece of aluminum in a test tube and adds sodium hydroxide solution. Bubbles of gas are produced and the outside of the test tube becomes hot to the touch. Which of the following is true?

a.	The reaction is endothermic, and the system gains energy from the surroundings.
b.	The reaction is exothermic, and the system loses energy to the surroundings.
c.	The reaction is endothermic, and the system loses energy to the surroundings.
d.	The reaction is exothermic, and the system gains energy from the surroundings.

b.	The reaction is exothermic, and the system loses energy to the surroundings.

6. A chemical reaction is carried out in a coffee cup calorimeter. The temperature of the water changes from 25.2 °C to 19.8 °C. Which statement is correct?

a.	The water loses energy, so the reaction is exothermic.
b.	The water gains energy, so the reaction is exothermic.
c.	The water loses energy, so the reaction is endothermic.
d.	The water gains energy, so the reaction is endothermic.

c.	The water loses energy, so the reaction is endothermic.

7. An enthalpy change is

a.	the difference in the kinetic energy of the reactants and the products in a chemical change.
b.	the difference in the potential energy of the reactants and the products in a chemical change.
c.	the difference in enthalpies of the reactants and the products in a chemical change.
d.	the sum of the PE and KE of the products.
e.	the sum of the PE and KE of the reactants.

a.	the difference in the kinetic energy of the reactants and the products in a chemical change.

8. Four common materials used to make pots for cooking are copper, stainless steel, aluminum, and glass. Pots made out of which material will heat up the fastest? 

c_copper = 0.385 J/(g  °C),   c_{stainless steel} = 0.510 J/(g  °C),   c_aluminum = 0.900 J/(g  °C),   c_glass = 0.753 J/(g  °C)

a.	aluminum	c.	stainless steel
b.	glass	d.	copper

d.

copper

9. What quantity of heat is required to raise the temperature of 0.500 g of graphite by 25.0 °C? 

(c_graphite= 0.710 J/(g  °C))

a.8.88 J  b. 0.355 J   c. 70.4 J   d. 35.5 J

a.8.88 J 

Q = mcΔT

Q = (0.5)(0.710)(25)

Q = 8.875

Q = 8.88J

10. Which equation correctly summarizes the information in this figure?

 

a.	H2O(g) → H2O(l) + 44 kJ
b.	ΔHcond = 44 kJ
c.	H2O(g) → H2O(l), ΔH = 44 kJ
d.	all of the above

a.	H2O(g) → H2O(l) + 44 kJ

11. Given the equation: 

N₂(g) + 2 O₂(g) → 2 NO₂(g), ΔH = 68 kJ

Which of the following is correct?

a.	N2(g) + O2(g) → NO2(g), ΔH= –68 kJ
b.	N2(g) + O2(g) → NO2(g), ΔH = 68 kJ
c.	NO2(g) →  N2(g) + O2(g), ΔH = –34 kJ
d.	NO2(g) →  N2(g) + O2(g), ΔH = 34 kJ

c.	NO2(g) →  N2(g) + O2(g), ΔH = –34 kJ

12. For an endothermic reaction, which of the following are true?

i. H_products > H_reactants

ii. H_reactants > H_products 

iii. ΔH is -ve

iv. ΔH is +ve

a.	i. and iii.	c.	ii. and iii.
b.	i. and iv.	d.	ii. and iv.

b.	i. and iv.

13. Which of the following reactions is exothermic?

a.	H2(g) + 1/2 O2(g) → H2O(g) ΔH = –243 kJ/mol
b.	1/2 N2(g) + 1/2 O2(g) + 90.7 kJ → NO(g)
c.	CO(g) + 111 kJ→ C(s) + 1/2 O2(g)
d.	1/2 H2(g) + 1/2 I2(g) → HI(g) ΔH = +26 kJ/mol
e.	H2O(g) →H2(g) + 1/2 O2(g) – ΔH = –243 kJ/mol

a.	H2(g) + 1/2 O2(g) → H2O(g) ΔH = –243 kJ/mol

14. What property would be appropriate to measure the reaction rate in the following reaction:

 

a.	Δ in conductivity	d.	change in pressure
b.	change in mass	e.	change in temperature
c.	change in colour

d.	change in pressure

15. The initial rate of the a reaction

a.	is dependent on the initial concentrations of the reactants.
b.	is always less than the average rate of the reaction.
c.	can be determined by studying the balanced equation.
d.	is equal to the instantaneous rate after 1.0 min.

a.	is dependent on the initial concentrations of the reactants.

16. The slope of a tangent on an graph of concentration vs. time will give which quantity?

a.	instantaneous rate	d.	chemical rate
b.	average rate	e.	all of the above
c.	initial rate

a.	instantaneous rate

17. If you compare the concentrations of reactant A at two different time intervals, the type of rate that can be determined is the:

a.	instantaneous rate	d.	chemical rate
b.	average rate	e.	all of the above
c.	initial rate

b.	average rate

18. In order for a collision to be effective, which of the following statements are true?

a.	The collision geometry of the reactants must be favourable
b.	The collision must occur with sufficient energy
c.	The collision must occur at the correct time
d.	Both a) and b) are correct
e.	All of a), b), and c) are correct

d.	Both a) and b) are correct

19. Which of the following is NOT a factor that affects the rate of a reaction?

a.	pressure of gases	d.	temperature
b.	[ ] of a solution	e.	all of the above
c.	nature of reactants

e.	all of the above

20. Increasing the surface area increases the rate of a reaction because

a.	the number of collisions increases.
b.	the activation energy decreases.
c.	the fraction of collisions that are effective increases.
d.	Only a) and b) are true.
e.	All a), b), and c) are true

a.	the number of collisions increases.

21. A catalyst increases the reaction rate by

a.	providing an alternative, low-energy pathway for the reaction
b.	increasing the kinetic energy of the reactant molecules
c.	increasing the number of collisions between reactant molecules
d.	colliding with the reactant molecules, increasing their energy, and adjusting their orientation

a.	providing an alternative, low-energy pathway for the reaction

22. Increasing the temperature of the reactants increases

a.	the number of collisions.
b.	the rate of the reaction.
c.	the fraction of collisions that are effective.
d.	Only a) and b) are true
e.	All a), b), and c) are true

e.	All a), b), and c) are true

23. Consider the following activation energy diagram.

 

From the activation energy diagram it  is seen that the reaction rate will ___i___ at ___ii___ temperature. The statement above is completed by information in row:

Row	___i___	___ii___
A.	decrease	lower
B.	increase	higher
C.	decrease	higher
D.	increase	lower

a. A   b. B   c. C   d. D

b. B  

B.

increase

higher

• At higher temperature T2, the red curve shows a greater area under the curve beyond Ea (to the right of the dashed line). This shaded area represents the fraction of particles that have enough energy to react.

• At lower temperature T1 the area beyond Ea​ is smaller, meaning fewer particles can overcome the activation energy barrier.

24. Maxwell Boltzmann diagrams give the relationship between fraction of molecules and energy. Which of the following graphs correctly represents an effective collision if the fraction of molecules capable of effective collision is given by the shaded position?

a.	c.
b.	d.

 

b.

25. For the above PE diagram, which letter represents the enthalpy change of the reaction?

a. A   b. B   c. C   d. D

c. C  

26. For the above PE diagram, ...which letter represents the activation energy of the forward reaction?

a. A   b. B   c. C   d. D

a. A  

27. ... which letter represents the location of the activated complex?

a. A   b. B   c. C   d. D

d. D

28. ... what kind of reaction is represented?

a.	nuclear	c.	exothermic
b.	endothermic	d.	barimetric

b.	endothermic

29. The activated complex

a.	is an unstable molecule.
b.	has the maximum potential energy possible.
c.	may continue on to produce products.
d.	may revert to reactants.
e.	All of the above.

e.	All of the above.

30. Which letter represents the activated complex of the rate determining step?

 

a. A  

b. B  

c. C  

d. D

c. C  

31. Given the following reaction: N₂(g) + 3 H₂(g) →2 NH₃(g)

If the concentration of hydrogen decreases by 3 mol/L in 45 seconds, what is the corresponding rate of disappearance of nitrogen?

a.	0.022 mol/L*s	d.	0.16 mol/L*s
b.	0.067 mol/L*s	e.	0.26 mol/L*s
c.	0.080 mol/L*s

a.	0.022 mol/Lïs

For every 1 mol of N2\​ that reacts, 3 mol of H2​ react.

Given:

Hydrogen decreases by 3 mol/L in 45 seconds.

Rate of disappearance of H2 = 3 mol/L ÷ 45 s = 0.0667 mol/L·s

From the balanced equation:

N2(g) + 3 H2(g) → 2 NH3(g)

This means for every 1 mol of N2 used, 3 mol of H2 are used.

So,
Rate of disappearance of N2 = Rate of disappearance of H2 ÷ 3
Rate of disappearance of N2 = 0.0667 mol/L·s ÷ 3 = 0.0222 mol/L·s

Since H₂ disappears 3 times faster than N₂ (because of the 3:1 ratio), the rate of N₂ disappearance is 1/3 the rate of H₂.

32. Consider the chemical reaction:

 H₂SO₄(aq) +2 NaOH(aq) → 2 H₂O(l) + Na₂SO₄(aq)

If the sulphuric acid is reacting at a rate of 1.60 mol/L*s, the sodium sulphate will be produced at a rate of

a.	0.40 mol/Lïs	d.	2.40 mol/Lïs
b.	0.80 mol/Lïs	e.	3.20 mol/Lïs
c.	1.60 mol/Lïs

c.	1.60 mol/Lïs

33. A reaction is found to be second order with respect to reactant A.  What would be the effect on the rate if the concentration of A were doubled?

a.	The rate would double
b.	The rate would quadruple
c.	The rate would decrease by half
d.	The rate would increase in an unpredictable way
e.	The concentration of A has no effect on the rate

b.	The rate would quadruple

34. An initial rate of reaction is usually obtained by measuring

a.	the rate at which products are consumed.
b.	the rate at which reactants are produced.
c.	the rate at which reactants are consumed.
d.	the temperature of the solution.
e.	the mass and volume of the products.

c.	the rate at which reactants are consumed.

35. What is the average rate of production of carbon dioxide for the system between 2.0 and 4.0 minutes, CH_4(g) = 2O_2(g) → CO₂ + 2H₂O(g) , if the concentration of carbon dioxide is 2.5 mol/L after 2.0 minutes and 7.2 mol/L after 4.0 minutes?

a.	0.426 mol/(L·min)	d.	2.35 mol/(L·min)
b.	1.18 mol/(L·min)	e.	42.6 mol/(L·min)
c.	0.952 mol/(L·min)

d.	2.35 mol/(L·min)

Given:

Reaction:
CH₄(g) + 2 O₂(g) → CO₂(g) + 2 H₂O(g)

CO₂ concentration at 2.0 minutes = 2.5 mol/L
CO₂ concentration at 4.0 minutes = 7.2 mol/L

---

Step 1: Find the change in concentration of CO₂

Change in [CO₂] = 7.2 mol/L – 2.5 mol/L = 4.7 mol/L

Step 2: Find the change in time

Change in time = 4.0 min – 2.0 min = 2.0 min

Step 3: Calculate average rate of production

Average rate = Change in [CO₂] ÷ Change in time
Average rate = 4.7 mol/L ÷ 2.0 min = 2.35 mol/L·min

Final Answer:

Average rate of production of CO₂ = 2.35 mol/L·min

36. Given the following graph of rate vs. concentration,

 

What must be the exponent of this reactant in the rate law for this process?

a.0   b. 1   c. 2   d. ½   e. 3

a.0  

This graph shows a horizontal line for initial rate as the concentration increases. That means:

• The rate stays constant, even though the concentration changes.

37. Experiments were carried out to determine the effect of changing concentration on the initial rate of reaction for a given reaction.  Given the data in the graph, what is the order of reaction with respect to this reactant?

 

a.0   b. 1   c. 2   d. 3

c. 2  

second-order, the graph would be a curve that steepens, showing a quadratic relationship.

38. Given the equation 2 Na(s) + 2 H₂O(l) → 2 NaOH(aq) + H₂(g), which of the following could be used to monitor the rate of the reaction?

a.	The decrease in mass of sodium.
b.	The volume of hydrogen gas produced.
c.	The pH of the solution.
d.	All of the above.

d.	All of the above.

39. The rate constant for a reaction is

a.	the sum of the exponents in the rate law equation.
b.	temperature dependent.
c.	determined from the balanced equation.
d.	the exponent used to describe the relationship between the initial concentration of a reactant and the reaction rate.

b.	temperature dependent.

40. If the rate law for a reaction is determined to be rate = k[X]¹[Y]²[Z]⁰, then the overall order of the reaction is

a.0   b. 1   c. 2   d. 3

d. 3

sum of the exponents

41. A plausible reaction mechanism (one that might work) must satisfy the following requirements:

a.	The balanced equation must be predicted by summing the elementary steps, and the mechanism must agree with the theoretically predicted equation.
b.	The balanced equation must be produced by summing the elementary steps, and the mechanism must agree with the experimentally determined rate law.
c.	The balanced equation must be produced by summing the elementary steps, and the mechanism must agree with the theoretically determined rate law.
d.	The balanced equation must be produced by summing the reaction intermediates, and the mechanism must agree with the experimentally determined rate law.

b.	The balanced equation must be produced by summing the elementary steps, and the mechanism must agree with the experimentally determined rate law.

42. The number of particles that would usually "collide" in an elementary step are

a. 1-2   b. 3-4   c. 5-6

d. Unlimited   e. no particles need to collide

a. 1-2  

43. A theoretical reaction is given: A + B₂ + C   AB + CB

The proposed mechanism for this reaction is as follows.

A + B₂  → AB + B (slow)

B + C   → BC   (fast)

Based on this mechanism, the rate law expression for this reaction is

a.	rate = k[A][B2]	c.	rate = k[B2][C]
b.	rate = k[A][B2][C]	d.	rate = k[A][C]

a.	rate = k[A][B2]

44. The radioisotope Pb-212 has a rate constant of 0.0654h^-1.  What is the half-life for this isotope?

a.	15.3 h	d.	10.6h
b.	0.0654 h-1	e.	0.050 h-1
c.	12120 h-1

d.

10.6h

To find the half-life, use the formula:

t₁/₂ = 0.693 ÷ k

Given:
k = 0.0654 h⁻¹

So,

t₁/₂ = 0.693 ÷ 0.0654 ≈ 10.6 hours

Correct answer: d. 10.6 h

45. Which statement is correct about the graph? 

Energy is lost …

a. from the surroundings into the system, indicating an exothermic reaction.

b. from the system into the surroundings, indicating an exothermic reaction.

c. from the system into the surroundings, indicating an endothermic reaction

d. from the surroundings into the system, indicating an endothermic reaction.

b. from the system into the surroundings, indicating an exothermic reaction.

46. Chlorine atoms can increase the rate of decomposition of ozone in the atmosphere. The mechanism for this reaction is:

(1) Cl + O₃ → ClO + O₂

(2) O₃ → O + O₂

(3) ClO + O → Cl + O₂

(4) O + O₃ → O₂ + O₂

If the rate law for this reaction is rate = k[O₃], the ______ reaction is the rate determining step.

a.	first
b.	second
c.	third
d.	fourth

b.

second

*Which of the following is true of the system and its surroundings ni aprocess in which ΔE_sys= (+100kJ)?

a.The system loses 100kJ of energy and the surroundings gain 100kJ of energy.

b. The system and the surroundings both lose 100kJ of energy.

c. The system gains 100kJ of energy and the surroundings lose 100kJ of energy.

d. The system and the surroundings both gain 100kJ of energy.

c. The system gains 100kJ of energy and the surroundings lose 100kJ of energy.

*An exothermic reaction is one where

a. heat is transferred from the surroundings into a system

b. heat is transferred from a system into the surroundings

c. kinetic energy is transformed into potential energy

d. there is no transfer of heat

b. heat is transferred from a system into the surroundings

*Enthalpy changes depend on the temperature and presssure under which a process occurss. However, the enthalpy change will be different at different presssures. Therefore, chemists often deal with standard enthalpy of reaction Δ_rH^o. The temperature and pressure conditions for standard enthalpy are:

a. 0°C and 1 atm

b. 25°C and 1 atm

c. 2.5°C and 10kPa

d. 2.5 K and 100 Pa

e. 25K and 1 atm

b. 25°C and 1 atm

*Which of the following substances (with specific heat capacity provided) would show the least temperature change upon absorbing 100.0 J of heat? (check ans)

a. 10.0g Ag, C_Ag= 0.235J/g°C

b. 10.0g H₂O, C_H2O=4.18 J/g°C

c. 10.0g ethanol, C_ethanol=2.42J/g°C

d. 10.0g Fe, C_Fe= 0.449J/g°C

e. 10.0 g Au, C_Au= 0.128J/g°C

b. 10.0g H₂O, C_H2O=4.18 J/g°C

*Calculate the amount of heat (in KJ) necesssary to raise the temperature of 47.8 g benzene by 57.0 K. The specific heat capacity of benzene is 1.05 J/g°C

a. 1.61 kJ

b. 16.6 kJ

c. 2.59 kJ

d. 2.86 kJ

e. 3.85 kJ

d. 2.86 kJ

*Determine the specific heat capacity of an alloy that requires 59.3 kJ to raise the temperature of 150.0g alloy from 298 K too 398K

a. 4.38 J/g°C

b. 2.29 J/g°C

c. 3.95 J/g°C

d. 2.53 J/g°C

e. 1.87 J/g°C

c. 3.95 J/g°C

*Given this information: N_2(g) + O₂ → 2NO_(g); ΔH_rxn= +80.5kJ

if H_p denotes the enthalpy of products and H_f denotes the enthalpy of reactants, then

a. H_{p >} H_f

b_. H_{p <} H_f

c_. H_{p =} H_f

d. H_{p >/=} H_f

a. H_{p >} H_f

*When 6.000 moles of glucose are combusted, 16 815 kJ of energy is produced. Which of the following chemical equations is an equivalent representation of this process?
a. 6C₆H₁₂O₆(s) + 36O₂(g) → 36CO₂(g) + 36H₂O(ℓ)   ΔH = (–2802.15 kJ)
b. 6C₆H₁₂O₆(s) + 36O₂(g) → 36CO₂(g) + 36H₂O(ℓ)   ΔH = 16815 kJ
c. C₆H₁₂O₆(s) + 6O₂(g) → 6CO₂(g) + 6H₂O(ℓ)     ΔH = (–16815 kJ)
d. C₆H₁₂O₆(s) + 6O₂(g) → 6CO₂(g) + 6H₂O(ℓ)     ΔH = (–2802.15 kJ)

d. C₆H₁₂O₆(s) + 6O₂(g) → 6CO₂(g) + 6H₂O(ℓ)     ΔH = (–2802.15 kJ)

*Which of the following statements is false concerning the heating and cooling curve of water?
a. Energy is absorbed to increase the kinetic energy of liquid water.
b. Energy is absorbed when liquid water evaporates.
c. Energy is released when liquid water freezes.
d. Energy is absorbed when H-bonds between water molecules are broken.
e. Energy is absorbed when bonds inside the water molecules are broken.

e. Energy is absorbed when bonds inside the water molecules are broken.

*The following graphs show the relationship between potential energy and progress of the reaction for four different reactions.
Which reaction has the smallest activation energy?
a. I  b. II  c. III  d. IV

d. IV

*X grams of sucrose give an enthalpy change of Y kJ/mol on combustion. What is the effect on enthalpy change when the mass of the sucrose is doubled?

a. The enthalpy change remains constant.

b. The enthalpy change doubles.

c. Enthalpy change is reduced to half.

d. ΔH stays the same.

e. Enthalpy becomes zero.

b. The enthalpy change doubles.

*The enthalpy of formation of an element in its most stable state, under standard conditions, is

a. constant.

b. changing.

c. the same as the reverse process.

d. infinity.

e.zero

e.zero

*The rate of a chemical reaction is doubled for every 10°C rise in temperature. This is because of a(n)
a. decrease in activation energy.
b. increase in activation energy.
c. increase in # of ineffective collisions.
d. increase in the # of effective collisions.
e. increase in enthalpy.

d. increase in the # of effective collisions.

*If we draw a potential energy diagram for an endothermic reaction, the potential energy (PE) of reactants is
a. less than PE of products.
b. equal to the PE of the products.
c. more than PE of the products.
d. equal to Eₐ of reverse reaction.
e. equal to Eₐ of forward reaction.

a. less than PE of products. (check ans)

*Consider the following activation energy diagram (a Maxwell-Boltzmann distribution).
From the above activation energy diagram, it is seen that the reaction rate will ___ at ___ temperature.
A. decrease / lower
B. increase / higher
C. decrease / higher
D. increase / lower
E. stay the same / any

B. increase / higher

*A reactant is found to have an order of zero in a chemical reaction. What would be the effect on the rate if the concentration of that reactant were decreased by half?
a. The rate would double.
b. The rate would quadruple.
c. The rate would decrease by half.
d. The rate would increase in an unpredictable way.
e. The concentration has no effect on the rate.

e. The concentration has no effect on the rate.

*A reaction has the following rate law: r = k[A]²[B]
What would be the effect on the rate if the concentration of A were doubled?
a. The rate would double.
b. The rate would quadruple.
c. The rate would decrease by half.
d. The rate would increase in an unpredictable way.
e. The concentration of A has no effect on the rate.

b. The rate would quadruple.

*Given the following balanced equation, determine the rate of reaction with respect to [NOCl]. If the rate of Cl₂ loss is 4.84 × 10⁻² M/s, what is the rate of formation of NOCl?
  2 NO(g) + Cl₂(g) → 2 NOCl(g)
a. 4.84 × 10⁻² M/s
b. 2.42 × 10⁻² M/s
c. 1.45 × 10⁻¹ M/s
d. 9.68 × 10⁻² M/s
e. 1.61 × 10⁻² M/s

d. 9.68 × 10⁻² M/s

*For the overall reaction CHCl₃(g) + Cl₂(g) → CCl₄(g) + HCl(g) the following reaction mechanism is determined by experimentation:
 CHCl₃(g) → CCl₃(g) + H(g)  (fast)
 CCl₃(g) + Cl₂(g) → CCl₄(g) + Cl(g)  (slow)
 Cl(g) + H(g) → HCl(g)       (fast)
What is the rate law for this reaction?
a. r = k[Cl₂]
b. r = k[CCl₃][CHCl₃]
c. r = k[CHCl₃][Cl₂]
d. r = k[CHCl₃][CCl₃]
e. r = k[CCl₃][Cl]

c. r = k[CHCl₃][Cl₂]

*Which of the following can affect the activation energy of a reaction?
a. Pressure of gases.
b. Concentration of a solution.
c. The presence of a catalyst.
d. Temperature.
e. All of the above may affect the Eₐ.

e. All of the above may affect the Eₐ.

*In an experiment where the concentration of one reactant in a chemical process is varied and the rate is measured, the following graph (initial rate vs concentration) is obtained:
What must be the exponent of this reactant in the rate law for this process?
a. 1/2  b. 0  c. 1  d. 2  e. 3

c. 1

*The 1st graph is for a ___ order reaction, while the 2nd graph is for a ___ order reaction.
a. 0 ; 1
b. 1 ; 2
c. 2 ; 1
d. 1 ; 0

b. 1 ; 2

*How many half-lives are required for the concentration of reactant to decrease to 25% of its original value?
a. 1  b. 3  c. 1.5  d. 2.5  e. 2

e. 2 (check ans)

*The rate constant for the first order decomposition for N₂O is 3.40s^-1. What is the half life of the decomposition?

a. 0.491s

b. 0.204 s

c. 0.235 s

d. 0.424 s

e. 0.294 s

b. 0.204 s

*Complete each statement

1. __________ is a measure of the average kinetic energy of the particles in a substance.

2. The energy values reported on food are Calories. A Cal is a (#) ________ calories

1. Temperature

2. 1000

Match the term with the correct definition below:

a.	thermochemistry	f.	open system
b.	ΔHof	g.	temperature
c.	specific heat capacity	h.	isolated system
d.	1st law of thermodynamics	i.	Hess’s law
e.	calorie	j.	state function

1. property that depends only on the condition of the system at the moment, not how it got there.

2. the amount of energy needed to increase the temperature of one gram of a substance by one degree Celsius 

3. a system that can exchange both matter and energy with the surroundings

4. a system that cannot exchange either energy or matter with the surroundings

5. energy can be converted from one form to another but cannot be created or destroyed

6. a measure of the average kinetic energy of all the particles of a sample of matter

7. the change in enthalpy when one mole of a compound is formed directly from its elements in their most stable state at standard ambient temperature and pressure

8. the enthalpy change of a physical or chemical process depends only on the initial and  final conditions of the process 

9. quantity of heat needed to raise the temperature of 1g of pure water by 1^oC.

10. the study of the energy changes involved in chemical and physical processes

1. J state function

2. C specific heat capacity

3. F open system

4. H isolated system

5. D 1st law of thermodynamics

6. G temperature

7. B ΔH^o_f

8. I Hess’s law

9. E calorie

10. A thermochemistry

Match the term with the correct definition below:

Classify each of the following reactions as exothermic or endothermic. Answer choices may be used more than once.

a. Exothermic

b. Endothermic

11. NaOH solution at 22 °C was mixed with HCl solution at 24 °C. The final solution had a temperature of 29 °C.

12. A piece of Mg was added to a test tube of acid. After reacting for 1 min the outside of the test tube was warm to the touch.

13. Ammonium nitrate was added to a beaker of water. Drops of water on the outside of the beaker solidified into ice.

14. Ba(OH)₂ crystals were mixed with NH₄Cl crystals at 25°C. A thermometer registers 10 °C after the reaction. 

11. A Exothermic

12. A Exothermic

13. B Endothermic

14. B Endothermic

1. The combustion of propane (C₃H₈) requires five oxygen molecules and produces three carbon dioxide and four waters, producing (-2202) kJ/mol.  Show three different ways of communicating this. (3 marks).

• rxn coordinate diagrams

• enthalpy diagrams

• thermochemical equations

  • ΔH included within the equation or after it

1. Thermochemical equations

C₃H₈(g) + 5O₂(g) → 3CO₂(g) + 4H₂O(g) ΔH = –2202 kJ (negative ΔH means exothermic)

ΔH can also be written as part of the products:

C₃H₈(g) + 5O₂(g) → 3CO₂(g) + 4H₂O(g) + 2202 kJ

(This shows that heat is released — exothermic reaction)

2. Enthalpy Diagram

labeled diagram showing:

• Y-axis: Enthalpy (H)

• X-axis: Reaction progress

• Reactants at a higher energy level than products

• Downward arrow labeled ΔH = –2202 kJ

• Shows energy is released

3. Reaction Coordinate Diagram

A diagram including:

• Y-axis: Enthalpy (H)

• X-axis:

• Reaction coordinate Curve rising to a peak (activation energy), then falling to the products Label:

• Reactants: C₃H₈ + 5O₂

• Products: 3CO₂ + 4H₂O

• Peak: Transition state

• Drop between reactants and products: ΔH = –2202 kJ

2. A kilogram of water and a kilogram of sand are at the same temperature. Do the two substances contain the same amount of heat energy? Explain. (2 marks)

No, they do not contain the same amount of heat energy.
Water has a high specific heat capacity (4.18 J/g°C), one of the highest among common substances. This means it can store much more heat energy per gram per degree than most materials, including sand. So even if water and sand have the same mass and temperature, the water holds more heat energy due to its greater ability to store thermal energy.

3. Use the typical rate of reaction graph (Concentration of Reactant vs. Time) and indicate (draw and explain) how to determine:  

a) an average rate of reaction; and 

b) an instantaneous rate of reaction (3 marks)

a) Average Rate of Reaction

How to determine:

• Pick two points on the concentration vs. time graph (for example, at time t₁ and t₂).

• Note their corresponding concentrations: [A]₁ and [A]₂.

• Draw a straight line (secant) connecting these two points.

Formula:
Average rate = ([A]₂ - [A]₁) / (t₂ - t₁)

This gives the slope of the secant line, which represents the average rate of reaction over that time period.

b) Instantaneous Rate of Reaction

How to determine:

• Choose a single point on the curve at a specific time (e.g., t = 10 s).

• Draw a tangent line at that exact point.

• Find the slope of the tangent line.

Formula:
Instantaneous rate = slope of the tangent line at that time

This represents how fast the reaction is happening at one specific moment.

4. 5.00 g of sodium hydroxide is added to enough water to reach 150 mL volume and then dissolved. Using a coffee-cup calorimeter, the temperature change of the water is measured to be 2.2^oC. 

a) Calculate the heat released per gram of sodium hydroxide dissolved.  (3 marks)

b) bonus: how does the wording ‘5.00 g of sodium hydroxide is added 150 mL of water’ effect the answer? (1 mark)

a)

Given:

• Mass of NaOH = 5.00 g

• Volume of water = 150 mL

• Temperature change (ΔT) = 2.2°C

• Specific heat capacity of water = 4.18 J/g·°C

• Assume the density of water = 1.00 g/mL → so 150 mL = 150 g of water

Step 1: Calculate total heat released (q):
q = m × c × ΔT
q = 150 g × 4.18 J/g·°C × 2.2°C
q = 1379.4 J

Step 2: Calculate heat released per gram of NaOH:
1379.4 J ÷ 5.00 g = 275.88 J/g

Final Answer: 276 J/g

b) The wording “5.00 g of sodium hydroxide is added to 150 mL of water” implies that the NaOH is added to 150 g of water, making the total mass of the solution around 155 g. However, if the calculation only uses the mass of water (150 g), it slightly underestimates the total heat absorbed, because the added NaOH also contributes mass and may slightly affect the heat capacity of the solution.

5. A sample of H₂O is heated, and its temperature rises from -5^oC to 110^oC. 

a) Draw and label a sketch graph for this process and indicate on the graph the state of the sample and the process occurring (what is happening) at each segment of the graph. (4 marks)

b) Calculate the energy expended in boiling 15g of water into steam.(2 marks)

c) Calculate the energy expended in heating 15g of water from 5^oC to 20^oC. (2 marks)

*a) Calculate the energy expended in melting 25g of ice into water (2 marks)

b) Calculate the energy expended in heating 25g of water at 95^oC to steam at 110^oC

6. Differentiate between the factors leading to an effective collision and an ineffective collision. (3 marks +)

Effective collisions result in a reaction, while ineffective collisions do not.

Effective collisions occur when reactant molecules collide with sufficient energy and correct orientation to break and form new chemical bonds. In other words, the collision results in a successful reaction. The minimum energy required for a reaction to occur is called the activation energy. The higher the activation energy, the less likely an effective collision will occur. Effective collisions are essential for chemical reactions to take place and are influenced by factors such as temperature, concentration, and surface area.

Ineffective collisions occur when reactant molecules collide with insufficient energy or incorrect orientation, resulting in no reaction. These collisions do not contribute to the overall reaction rate and are therefore considered a waste of energy.

Ineffective collisions can be caused by factors such as low temperature, low concentration, and insufficient surface area. Increasing the temperature, concentration, or surface area can increase the number of effective collisions and therefore increase the reaction rate.

7. Determine the enthalpy (ΔH) of the following reaction: 

2 H₂S(g) + SO₂(g) → 3 S(s) + 2 H₂O(g)

given the following equations: (5 marks)

H₂O(g) → H₂(g) +  ½ O₂(g); ΔH = 241.8 kJ

H₂S(g) → H₂(g) + S(s); ΔH = 20.6 kJ

S(s) + O₂(g) → SO₂(g); ΔH = (–296.8) kJ

8. Calculate the enthalpy change for the reaction given: (4 marks)

C₃H₈(g) + 5O₂(g) → 3CO₂(g) + 4H₂O(g)

Standard enthalpies of formation ( Hf°) are:

C₃H₈(g) = (–103.85) kJ/mol;  

CO₂(g) = (–393.5) kJ/mol;   

H₂O(g) = (–285.8) kJ/mol

9. For the reaction A + B + 2 C → ABC₂, the following data were obtained:

Run	[A] (mol/L)	[B] (mol/L)	[C] (mol/L)	Rate (mol/(Ls))
1	0.120	0.220	1.25	2.14 x 10–3
2	0.120	0.220	2.50	2.14 x 10–3
3	0.120	0.440	1.25	4.28 x 10–3
4	0.240	0.220	1.25	8.56 x 10–3

a) Determine the rate law for this reaction (explain your reasoning). (3 marks)

b) Determine the value of the rate constant. (2 marks)

*Use the following data to calculate the rate law for the system, and a value for the rate constant. (5 marks)
  NO(g) + H₂(g) → HNO₂(g)

Experiment	NO (mol/L)	H₂ (mol/L)	Initial Rate of Reaction (mol/L·s)
1	0.001	0.004	0.002
2	0.002	0.004	0.008
3	0.003	0.004	0.018
4	0.004	0.001	0.008
5	0.004	0.002	0.016
6	0.004	0.003	0.024

*What is the enthalpy change for the formation of one mole of butane gas (C₄H₁₀) from its elements?
            4C(s) + 5H₂(g) → C₄H₁₀(g)
The following known equations, determined by calorimetry, are provided: (4 marks)
(1) C₄H₁₀(g) + 13/2 O₂(g) → 4CO₂(g) + 5H₂O(g)  ΔH° = –2657.4 kJ
(2) C(s) + O₂(g) → CO₂(g)  ΔH° = –393.5 kJ
(3) 2H₂(g) + O₂(g) → 2H₂O(g)  ΔH° = –483.6 kJ

*Given the following standard heats of formation, what is the ΔH° in kilojoules for the combustion of 1 mol of ethanol, C₂H₅OH(l), to form gaseous carbon dioxide and gaseous water, given the reaction:
  C₂H₅OH(l) + 3 O₂(g) → 2 CO₂(g) + 3 H₂O(g)  (3 marks)

Substance	ΔH°f (kJ/mol)
H₂O(g)	–241.8
H₂O(l)	–286
CO₂(g)	–393.5
C₂H₅OH(l)	–235.2