Chemistry Exam 3

3.2

1.9M

Consider the following reaction: 2 SO2(g) + O2(g) ⇌ 2 SO3(g) ;   Kc = 1.7 × 108

The concentrations at equilibrium are: [SO2]eq = 0.0034 M,  [O2]eq = 0.0018 M.

 Determine the equilibrium concentration of SO3(g). 

2.6 × 10^-5

The equilibrium constant is given for one of the reactions below.  Determine the value of the missing equilibrium constant.

H2(g) + Br2(g) ⇌ 2 HBr(g) K1 = 3.8 × 104

2 HBr(g) ⇌ H2(g) + Br2(g) K2 =  ?

5.7 × 10^-7

The reaction below has a Kp value of 3.3 × 10-5.  What is the value of Kc for this reaction at 700 K?

2 SO3(g) ⇌ 2 SO2(g) + O2(g)

0.021

2.50 mol NOCl was placed in a 2.50 L reaction vessel at 400ºC.  After equilibrium was established, it was found that 28% of the NOCl had dissociated according to the equation 

2NOCl(g) →← 2NO(g) + Cl₂(g).

Calculate the equilibrium constant, K_c, for the reaction.   

17

A reaction mixture A(g) + 2B(g) →← C(g) was allowed to come to equilibrium.  The initial amounts of reactants placed into a 5.00 L vessel were 1.0 mol A and 1.8 mol B.  After the reaction reached equilibrium, 1.0 mol of B was found.  Calculate K_c for this reaction.  

7.5

The brown gas NO₂ and the colorless gas N₂O₄ exist in equilibrium, 2NO₂ →←  N₂O₄.  In an experiment, 0.625 mole of N₂O₄ was introduced into a 5.00 L vessel and was allowed to decompose until equilibrium was reached.  The concentration of N₂O₄ at equilibrium was 0.0750 M.  Calculate K_c for the reaction.      

0.152 atm

Pure NO₂(g) is placed into a vessel at a pressure of 0.500 atm. At equilibrium, the total pressure inside the reaction vessel is 0.674atm. The reaction that takes place is:  2NO₂(g) →← 2NO(g) + O₂(g) .  Calculate the equilibrium partial pressure of NO₂.    

2.7M

For this reaction 3H₂(g) + N₂(g) →←  2NH₃(g), K_c = 6.0 ◊ 10^–2 at 500°C.  The concentrations at equilibrium are: 0.250 M H₂ and 0.050 M NH₃.  What is the equilibrium concentration of N₂?                  

Number 1

For the equilibrium reaction 2SO₂(g) + O₂(g) →←  2SO₃(g), ΔHº_rxn  = –198 kJ/mol.  Which one of these factors would cause the equilibrium constant to increase?

1. Decreasing the temperature

2. Increasing the pressure

A catalyst does not change the equilibrium constant because it does not alter the energies of the reactants or products

Explain why addition of a catalyst does not affect the equilibrium constant for a reaction.

17.3

5.00 mol of ammonia are introduced into a 5.00 L reactor vessel at high temperatures. The reaction that takes place is:

2NH₃(g) → ← 3H₂(g) + N₂(g)

At equilibrium, 1.00 mole of ammonia remains.  Calculate K_c for the reaction.      

7.1g

Calcium carbonate decomposes at high temperatures to give calcium oxide and carbon dioxide. 

CaCO₃(s) →← CaO(s)  +  CO₂(g)

K_p for this reaction is 1.16 atm at 800°C. 

A 5.00 L vessel containing 10.0 g of CaCO₃(s) was evacuated to remove the air, sealed, and then heated to 800°C. Ignoring the volume occupied by the solid, what will be the mass of the solid in the vessel be once equilibrium is reached?

66.7

Given the reaction PCl3(g) + Cl2(g) → PCl5(g)

An equilibrium mixture at 450 K contains 

 PCl3 = 0.124 atm, 

 Cl2= 0.157 atm, and 

 PCl5= 1.30 atm.

What is the value of Kp at this temperature?

4.0 × 10^-2

The reaction below has a Kc value of 61.  What is the value of Kp for this reaction at 200 ᵒC?

N2(g) + 3 H2(g) ⇌ 2 NH3(g)

0.253 M CO₂, and 0.053 M H2

For the reaction CO₂(g) + H₂(g) ⇌ H₂O(g) + CO(g) , Kc = 1.6 at 990ºC. 

Calculate the concentration of carbon dioxide and hydrogen in the final equilibrium mixture obtained by initially adding 2.00 mol of CO₂ , 1.00 mol of H₂, to a 5.00 L reactor at 990ºC.   

a. 19.5

b. Yes

c. [H₂] = 0.250 M, [I₂] = 0.041 M, [HI] = 0.746 M)

A reaction mixture of 0.623 M H₂, 0.414 M I₂ and 2.24 M HI is placed in a steel container. The reaction that takes place is:

H₂(g) + I₂(g)   2 HI (g) K_c = 54.3 at 430 ºC

1. Calculate the reaction quotient, Qc, for the initial mixture.

2. Will the reaction proceed towards making HI?

3. Calculate the concentration of these species at equilibrium.

0.020

The initial concentration of [CH4] = 0.114 M. At equilibrium, the mixture contains [C₂H₂] = 0.035 M. What is the value of the equilibrium constant, K_c, at this temperature? 

2CH4(g) →← C2H2(g) + 3H2(g)

interdependent

The concentrations of Hb, O2, and HbO2 are all

the condition wherein the rates of the forward and reverse reactions are equal

Dynamic equilibrium

equal

At equilibrium, the rates of the forward and reverse reactions are _____ at equilibrium

the rate of the forward reaction equals the rate of the reverse reaction

Chemical equilibrium

concentration, pressure, volume, temperature

Factors that affect chemical equilibrium:

temperature dependent

Dynamic process is ________

relates the molar concentrations of the products and reactants after the equilibrium has been reached

Equilibrium constant

inverted

When the reaction is written in reverse (i.e., backward), the equilibrium constant, K, is

reaction quotient. predicts in which direction the reaction will proceed from a starting set of concentrations for all of the components of a reaction

Qc

reactants will be converted into products; reaction goes reactants → products

Qc<Kc

the reaction will proceed in the reverse direction. The products will decrease and reactants will increase.

Q>K

the reaction will proceed in the forward direction. The products will increase and reactants will decrease.

Q<K

the reaction is at equilibrium. The products and reactants will not change.

Q=K

• Initial concentration

• Change in concentration to reach equilibrium

• Equilibrium concentration

ICE stands for

If an external stress is applied to a system at equilibrium, the system will adjust to reduce this stress and will re-establish new concentrations, keeping Kc constant (Kc is temperature dependent)

La Chatelier’s Principle

restored

If the conditions are changed, the concentrations of all the chemicals will change until equilibrium is ______

minimize

It says that if a system at equilibrium is disturbed, the position of equilibrium will shift to _________ the disturbance

favoring

If the temperature is increased, the system will shift to reduce this “added heat” by ______ the endothermic reaction

increases, changing, reducing

The equilibrium will be reached sooner because the catalyst ______ the rate of reaction by ______ the mechanism and ______ the activation energy

do not

Catalysts ______ affect the position of equilibrium

neutralize bases

Acids have the ability to …

hydrochloric acid

HCl

sulfuric acid

H2SO4

Nitric acid

HNO3

Acetic acid

HC2H2O2

Citric acid

H3C6H5O7

Carbonic acid

H2CO3

Hydroflouric acid

HF

Phosphoric acid

H3PO4

COOH

Carboxylic acids have a _____ group

H

Only the ___ in the (carboxylic acid) group is acidic

neutralize acids

Bases have the ability to …

1. Sodium hydroxide

2. Potassium hydroxide

3. Sodium bicarbonate

4. Sodium carbonate

5. Ammonia

Name the 5 common bases

Sodium hydroxide

NaOH

Potassium hydroxide

KOH

Sodium bicarbonate

NaHCO3

Sodium carbonate

Na2CO3

Ammonia

NH3

1. Hydrochloric acid

2. Sulfuric acid

3. Nitric acid

4. Acetic acid 

5. Citric acid

6. Carbonic acid 

7. Hydroflouric acid 

8. Phosphoric acid

Name the 8 common acids

H3O+

Hydronium ion formula

H+

An arrhenius acid releases ___ into solution

OH-

An arrhenius base releases ___ into solution

an acid that is an electron pair acceptor

Lewis acid

an base that is an electron pair donor

Lewis base

an acid that is a proton donor

Bronsted-Lowry acid

a base that is a proton donor

Bronsted-Lowry acid

an acid that fully dissociates in water

Strong acid

a base that fully dissociates in water

Strong base

an acid that doesn’t fully dissociate in water

Weak acid

a base that doesn’t fully dissociate in water

Weak base

when dissolved in water, they dissociate into ions

Why are acids and bases electrolytes

H2CO3 and HCO3-

In the reaction H2CO3 + H2O ⇌ HCO3 – + H3O+ , the Brønsted acids are

CO32-

Identify the conjugate base of HCO3 – in the reaction: CO3 2– + HSO4 – ⇌ HCO3 – + SO4 2–

H2CO3

Identify the conjugate acid of HCO3 – in the reaction and circle it: HCO3 – + HPO4 2– ⇌ H2CO3 + PO4 3–

-0.40

What is the pH of [H + ] in a 2.5 M HCl solution?

2.0 × 10^-3 M

The [OH– ] in a 1.0 x 10^–3 M Ba(OH)2 solution is

2.0 × 10^-13 M

What is the H+ ion concentration in a 4.8 x 10–2 M KOH solution?

a. 0.0057M

b. 3.4 × 10^-4

A 0.10 M HF solution is 5.7% ionized.

a) Calculate the [H + ]

b) calculate the Ka of HF

5.7%, pH= 2.1

Calculate the percent ionization of HNO2 in a 0.14 M HNO2 solution, knowing that the Ka of HNO2 is Ka = 4.6 x 10-4 . What is the pH of this solution?

a. 0.0025 M

b.  1.4 × 10^-4

If a 0.048 M lactic acid, HA, solution is 5.2% ionized, determine:

a) the [H3O+ ] concentration at equilibrium

b) the acidity constant, Ka, for this acid

12.65

Determine the pH of a KOH solution made by mixing 0.251 g KOH with enough water to make 100.0 mL of solution

0.004M

Calculate the [H + ] in lemon juice that has a pH 2.40.

a. 2.46

b. 0.0158M

a) Calculate the pH of a 3.5 x 10–3 M HNO3 solution

b) What is the [HNO3] if the pH of the solution is pH 1.80?

100

The pH of coffee is approximately pH 5. How many times greater is the [H+ ] in coffee than in pure water, pH 7 ?

NH3(aq) + H2O(l) →← NH4+(aq) + OH-(aq)

An aqueous solution of ammonia is basic. Write the net ionic equation that explains this observation.

water, aluminum oxide, zinc oxide

List 3 amphoteric species:

2.56 × 10^-11 M

Calculate the [OH⁻] in a solution that contains 3.9 × 10-4 M H3O⁺ at 25°C.

4 × 10^-5 M

The pOH of a solution is 9.60. Calculate the hydronium ion concentration in this solution.

HF because HF is the strongest bond so it ionizes the least in water

Identify the weakest acid and explain how you made the decision: HF HCl HBr HI

A. 2NO2 + H2O → HNO2 + HNO3

B. LiOH → Li+ + OH-

C. K2O + H2O → 2KOH

D. NaCl → Na+ + Cl-

E. Ca(OH)2 → Ca²+ + 2OH-

Reaction A produces an acidic solution that dissolves in water

Write the reaction with water for the following compounds. Which of the following produces an acidic solution when dissolved in water?

A) NO2

B) LiOH

C) K2O

D) NaCl

E) Ca(OH)2

SO3 + H2O → H2SO4

N2O5 + H2O → 2HNO3

The oxides SO3 and N2O5 will form acids in water. Write the two reactions.

8.5 × 10^-6

A 0.294 M weak acid, HA, solution has a pH 2.80. Determine the Ka of the acid.

11.26

Determine the pH of a 0.188 M NH3 solution at 25°C. The Kb of NH3 is 1.76 × 10-5

D

Which of the following weak acids has the strongest conjugate base?

A) acetic acid, Ka = 1.8 × 10-5

B) nitrous acid, Ka = 4.5 × 10-4

C) dihydrogen phosphate ion, Ka = 6.2 × 10-8

D) hydrocyanic acid, Ka = 4.0 × 10-10

E) benzoic acid, Ka = 6.3 × 10-5

2.7 × 10^-3 M

pH = 2.57

What is the hydronium ion concentration and the pH of a 0.400 M acetic acid solution with Ka = 1.8 × 10-5? The equation for the dissociation of acetic acid is: CH3CO2H + H20 →← H3O+ + CH3CO2-

9.47

Calculate the pH of a 1.60 M CH3COONa solution. Ka for acetic acid, CH3COOH, is 1.8 × 10-5.

0.056 M

Determine the ammonia concentration of an aqueous solution that has a pH 11.00. The equation for the dissociation of NH3 (Kb = 1.8 × 10-5) is: NH3 + H2O →← NH4+ + OH-

4.03

Calculate the pH of a 0.020 M carbonic acid solution, H2CO3(aq), that has the stepwise dissociation constants Ka1 = 4.3 × 10-7 and Ka2 = 5.6 × 10-11

4.97

What is the pH of a 0.20 M solution of NH4Cl? Kb(NH3) = 1.8 x10–5

9.57

Morphine, C17H19NO3 (or R3N in short notation) is often used to control severe postoperative pain. What is the pH of the solution made by dissolving 25.0 mg of morphine in 100. mL of water? (For morphine, Kb = 1.62 10–6 .)

R3N + H2O →← R3NH+ + HO-

11.40

Calculate the pH of a solution containing 0.20 g of NaOH in 2.00 L solution.