Thermochemistry Quiz

The value of enthalpy change for the reaction below is -482 kJ. Calculate the heat (kJ) released to the surroundings when 12.0 g of CO(gas) reacts completely.

2CO (g) + O₂ (g) → 2CO₂ (g)

103

What is the change in internal energy in joules for a system that releases 154 J of heat and does 125 J of work on its surroundings?

-279 J

For the reaction: 2A + B2 → 2AB ΔH = +50.0 kJ.

The reaction is endothermic.

When heat is absorbed by the system and work is done by the system on the surroundings then

q is positive and w is negative.

Ethylene glycol, used as a coolant in automotive engines, has a specific heat capacity of 2.42 J/g°C. Calculate q when 3.65 kg of ethylene glycol is cooled from 132°C to 85°C.

-420 kJ

What is ΔH°rxn for the following reaction?

H3AsO4(aq) + 4H2(g) → AsH3(g) + 4H2O(l)

Substance	ΔH°f(kJ/mol)
AsH3(g)	171.5
H3AsO4(aq)	–904.6
H2O(l)	–285.8

–67.1 kJ/mol

What is ΔH°rxn for the following reaction?

SiO2(s) + 4HCl(g) → SiCl4(g) + 2H2O(g)

Substance	ΔH°f(kJ/mol)
SiO2(s)	–859.3
SiCl4(g)	–662.8
HCl(g)	–92.3
H2O(g)	–241.8

82.1 kJ/mol

An endothermic reaction causes the surroundings to

decrease in temperature.

What is ΔH°rxn for the following reaction?

NO2(g) + CO(g) → CO2(g) + NO(g)

Substance	ΔH°f(kJ/mol)
NO(g)	+90.4
NO2(g)	+33.85
CO(g)	–110.5
CO2(g)	–393.5

–226.5 kJ

A system receives 575 J of heat and delivers 424 J of work. What is the change in the internal energy, ΔU, of the system?

150. J

If 75.4 J of energy is absorbed by 0.25 mol of CCl4 at constant pressure, what is the change in temperature? The specific heat of CCl4 is 0.861 J/g·°C.

2.3°C

When 0.560 g of Na(s) reacts with excess F2(g) to form NaF(s), 13.8 kJ of heat is evolved at standard-state conditions. What is the standard enthalpy of formation (ΔH°f) of NaF(s)?

  2Na(S) + F₂ → 2NaF  ΔH°????

Hint: First change the gram of sodium to mole of sodium, with this amount of the mole of sodium, 13.8 kJ released.

 Then figure out how much energy could be released per one mole of sodium.

–567 kJ/mol

Octane (C8H18) undergoes combustion according to the following thermochemical equation.

2C8H18(l) + 25O2(g) → 16CO2(g) + 18H2O(l)  ΔH°rxn = –1.0940 × 104 kJ/mol

What is the standard enthalpy of formation of liquid octane?

ΔH°f(CO2(g)) = –393.5 kJ/mol and ΔH°f(H2O(l)) = –285.8 kJ/mol

–250 kJ/mol

A system absorbs 21.6 kJ of heat while performing 6.9 kJ of work on the surroundings. If the initial internal energy, U, is 61.2 kJ, what is the final value of U?

75.9 kJ

You drove your car using 2 gallons of gasoline.  You have destroyed the chemical energy stored in the gasoline.

False

Given that CaO(s) + H2O(l) → Ca(OH)2(s), ΔH°rxn = –64.8 kJ/mol, how many grams of CaO must react in order to liberate 525 kJ of heat?

454 g

How many calories are in 854.3 J? (1 cal = 4.184 J)

204.2 cal

Benzene is a starting material in the synthesis of nylon fibers and polystyrene (styrofoam). Its specific heat capacity is 1.74 J/g·°C. If 16.7 kJ of energy is absorbed by a 225-g sample of benzene at 20.0°C, what is its final temperature? 

62.7°C

If two solutions are mixed together in a container and the container "feels hot", then

The reaction is exothermic.