Chapter 15 - Chemical Equilibrium

2NO(g) + Br2(g) → 2NOBr(g) Kc = 4.0 What is the equilibrium constant of the following reaction? 4NO(g) + 2Br2(g) → 4NOBr(g) Kc = ?

16

Which of the following will increase the yield of H2? Mg2+(aq) + 2H+(aq) ⇌ H2(g) + Mg(s) Choose only ONE best answer. A Decreasing the pH B Removing Mg(s) C Removing Mg2+(aq) D Increasing the pressure E Adding Mg(s)

Decreasing the pH To increase the yield of H2, the reaction needs to shift right. Decreasing the pH (making the solution more acidic) increases the [H+], a reactant, therefore resulting in a shift to the right.

Which of the following is/are always true about a reaction at equilibrium? I. [reactants] = [products] II. forward rate = reverse rate III. Δ[reactants] / Δt = 0

II and III

For an elementary reaction the forward and reverse rate constants are equal to 3.0 x 10-4s-1 and 2.0 x 10-6s-1. What is the equilibrium constant for this reaction?

Kc = kf / kr 1.5 x 102

Kp=

Kc(RT)^delta n

2SO2+O2<-->2SO3 Kc=278 Based on the reaction, what is the equilibrium constant for... SO2+1/2 O2<-->SO3

Kc= [SO3]/[SO2][O2]^1/2 (278)^1/2

2SO2+O2<-->2SO3 Kc=278 What is the equilibrium constant expression?

Kc= [SO3]^2[O2]/[SO3]^2 278/1

If K>>1, what does equilibrium favor?

Products

The following reaction is allowed to reach equilibrium. A2(g) + B2(g) → 2AB(g) If the partial pressures of A2 and B2 are each doubled and the concentration of AB is tripled, then which of the following is true? Choose only ONE best answer. A The reaction is still at equilibrium B Q > K and the reaction shifts to the left C Q < K and the reaction shifts to the left D Q > K and the reaction shifts to the right E Q < K and the reaction shifts to the right

Q > K and the reaction shifts to the left

If K<<1, what does equilibrium favor?

Reactants

10^-3<K<10^3, what does equilibrium favor?

Reactants and Products

What is the result when Q>K

Shifts Left

HF dissociates to a greater extent as the temperature is raised. Which of the following conclusions could be deduced from this fact? HF(aq) ⇌ H+(aq) + F-(aq) Choose only ONE best answer. A HF is less acidic at higher temperatures. B The dissociation of HF results in an increase in entropy. C The dissociation of HF evolves heat. D The dissociation of HF is endothermic. E HF is more stable at higher temperatures.

The dissociation of HF is endothermic.

For the following reaction Kc = 107. 2Tl(s) + Co2+(aq) ⇌ 2Tl+(aq) + Co(s) If [Co2+] = 0.01M and [Tl+] = 2.0M then which of the following is true? Choose only ONE best answer. A The reaction is at equilibrium. B The reaction must proceed to the left to reach equilibrium. C The reaction must proceed to the right to reach equilibrium. D The forward rate is faster than the reverse rate. E Not enough info is given to determine whether the reaction is at equilibrium or not.

The reaction must proceed to the left to reach equilibrium.

Where will an increase in pressure shift to?

The side with the fewer number of mols of gas

When EQ is small, what can be ignored?

X in denominator

Four moles of NO are placed in a 1.0L vessel and are allowed to reach equilibrium for the following reaction. 2NO(g) ↔ N2(g) + O2(g) At equilibrium there are 1.98 moles of N2 present. How many moles of NO are present in the mixture?

0.04

R=

0.0821

If for the following reaction Kc = 107. 2Tl(s) + Co2+(aq) ⇌ 2Tl+(aq) + Co(s) Then what is the value of the equilibrium constant for the following reaction? 4Tl(s) + 2Co2+(aq) ⇌ 4Tl+(aq) + 2Co(s)

1.1 x 104

2A2(g) + B2(g) → 2A2B(g) Kc = 100 What is the equilibrium constant of the following reaction? 2A2B(g) → 2A2(g) + B2(g) Kc = ?

1/100

What is the equilibrium constant expression for the following reaction? 4Al(s) + 3O2(g) → 2Al2O3(s)

1/[O2]^3

Ten moles of SO2 and six moles of O2 are placed in a 2.0L vessel and are allowed to reach equilibrium for the following reaction. 2SO2(g) + O2(g) ↔ 2SO3(g) At equilibrium there are two moles of SO2 present. What is the value of the equilibrium constant, Kc, for this reaction?

16

If 4 moles of H2 and 4 moles of Br2 are placed in a 2.0L container, what is the equilibrium concentration of HBr? H2(g) + Br2(g) ↔ 2HBr(g) Kc = 12.8

2.56M

Six moles of NO are placed in a 1.0L vessel and are allowed to reach equilibrium for the following reaction. 2NO(g) ↔ N2(g) + O2(g) At equilibrium there are 2.97 moles of N2 present. What is the value of the equilibrium constant, Kc, for this reaction?

2450

For which of the following reactions is Kp = Kc? Choose only ONE best answer. A 2NH3(g) → N2(g) + 3H2(g) B N2O4(g) → 2NO2(g) C 2NO(g) → N2(g) + O2(g) D 2H2(g) + O2(g) → 2H2O(g) E CaCO3(s) → CaO(s) + O2(g)

2NO(g) → N2(g) + O2(g)

A rigid container was charged with 2atm partial pressures for both H2 and Cl2. At equilibrium the partial pressure of HCl is 3atm. What is the equilibrium constant for the following reaction? H2(g) + Cl2(g) → 2HCl(g)

36

If for the following reaction Kc = 1.7 x 107 Ag+(aq) + 2NH3(aq) ⇌ Ag(NH3)2+(aq) Then what is the value of the equilibrium constant for the following reaction? 3Ag+(aq) + 6NH3(aq) ⇌ 3Ag(NH3)2+(aq)

4.9 x 1021

If for the following reaction Kc = 2.0 x 10-9 HOBr(aq) ⇌ H+(aq) + BrO-(aq) Then what is the value of the equilibrium constant for the following reaction? H+(aq) + BrO-(aq) ⇌ HOBr(aq)

5.0 x 108

What is the equilibrium concentration of OCl- in 0.10M HOCl? HOCl (aq) ↔ H+(aq) + OCl-(aq) Kc = 2.9x10-8

5.4 x 10-5M

A(g) + B(g) → C(g) Kc = 0.25 What is the equilibrium constant of the following reaction? 3C(g) → 3A(g) + 3B(g) Kc = ?

64

A rigid container was charged with 4atm N2O4. At equilibrium the partial pressure of N2O4 is 1atm. What is the equilibrium partial pressure of NO2? N2O4(g) → 2NO2(g)

6atm

For the following reaction at equilibrium PH2 = 0.5atm, PN2 = 4atm, and PNH3 = 0.25atm. Calculate Kp. 2NH3(g) → N2(g) + 3H2(g)

8

A rigid container was charged with 4M concentrations of both A2 and B2. What is the equilibrium concentration of AB? A2(g) + B2(g) → 2AB(g) Kc = 4.0 x 10-8

8 x 10^-4M

Which of the following can result in a change in the value of an equilibrium constant? Choose only ONE best answer. A A change in pressure B A change in temperature C Increasing the concentration of reactants D Adding an inert gas E Decreasing the concentration of products

A change in temperature

Which of the following changes to the following reaction at equilibrium would result in a shift to the right? Sn(s) + 2Cl2(g) ⇌ SnCl4(g) ΔH° = -471.5kJ Choose only ONE best answer. A Addition of SnCl4 B A decrease in pressure C A decrease in temperature D Addition of Sn E None of these

A decrease in temperature

Which of the following will shift the equilibrium of the following reaction to the right? N2(g) + 3H2(g) ⇌ 2NH3(g) Choose only ONE best answer. A Adding NH3(g) B Removing N2(g) C Removing H2(g) D Increasing the volume of the reaction vessel E Adding H2(g)

Adding H2(g)

2C(s)+O2(g)<-->2CO(g)+Heat What will be the result of increasing temperature?

Adding heat to the reactants, shifts left, endothermic

Which of the following changes to the following reaction at equilibrium would result in a shift to the right? CaO(s) + CO2(g) ⇌ CaCO3(s) Choose only ONE best answer. A Addition of CaO B Removal of CaO C Removal of CaCO3 D Addition of CO2 E Addition of CaCO3

Addition of CO2

Delta n=

Change in the mols of gas Products-Reactants NO DONT INCLUDE SOLIDS OR LIQUIDS

Which of the following will result in a shift to the right for the following reaction at equilibrium? 2H2(g) + O2(g) → 2H2O(g) ΔH˚ = -484kJ Choose only ONE best answer. A Decrease in [O2] B Increase in [H2O] C Decrease in temperature D Decrease in pressure E Decrease in [H2]

Decrease in temperature A negative ΔH indicates an exothermic reaction (heat is a product). An decrease in temperature would be the removal of heat (a product) which would result in a shift to the right.

Which of the following will maximize the production of CO(g)? 2C(s) + O2(g) ⇌ 2CO(g) ΔH = -566kJ Choose only ONE best answer. A Removing O2 B Increasing the pressure C Decreasing the temperature D Decreasing the volume E Adding C(s)

Decreasing the temperature

What is the result when Q=K

Equilibrium

Will the delta H be exothermic or endothermic?

Exo, negative, on product side

Which of the following will result in a shift to the left for the following reaction at equilibrium? 2SO3(g) → 2SO2(g) + O2(g) ΔH˚ > 0 I. increase in [O2] II. increase in temperature III. increase in pressure

I and III

Which of the following will result in a shift to the right for the following reaction at equilibrium? A2(g) + B2(g) → 2AB(g) I. increase in [A2] II. decrease in [B2] III. decrease in [AB]

I and III

Le Chatelier's Principle

If a stress is placed on a system at equilibium, the system wi;; respond to counteract the stress

2C(s)+O2(g)<-->2CO(g)+Heat What would be the result of adding an inert gas?

Increase pressure but no shift because concentration doesn't change

Which of the following will increase the value of the equilibrium constant for the following reaction? CaCO3(s) ⇌ CaO(s) + CO2(g) ΔH = 178kJ Choose only ONE best answer. A Adding CaCO3 B Removing CO2 C Increasing the temperature D Decreasing the temperature E Increasing the pressure

Increasing the temperature

Which of the following describes a reaction for which mostly reactants are present at equilibrium? Choose only ONE best answer. A Kc = 1.0 x 108 B Kc = 2 C Kc > 0 D Kc < 0 E Kc = 1.0 x 10-8

Kc = 1.0 x 10-8

Which of the following describes a reaction for which mostly products are present at equilibrium? Choose only ONE best answer. A Kc = 1.0 x 108 B Kc = 2 C Kc > 0 D Kc < 0 E Kc = 1.0 x 10-8

Kc = 1.0 x 108

2C(s)+O2(g)<-->2CO(g) What is the equilibrium constant expression for the reaction above?

Kc=[CO2]^2/[O2]

2SO2+O2<-->2SO3 Kc=278 Based on the reaction, what is the equilibrium constant for... SO3<-->SO2+1/2O2

Kc=[SO2][O2]^1/2/[SO3] (1/278)^1/2

2SO2+O2<-->2SO3 Kc=278 Based on the reaction, what is the equilibrium constant for... 2SO3<-->2SO2+O2

Kc=[SO2]^2[O2]/[SO3]^2 1/278

Which of the following changes to the following reaction at equilibrium would result in a shift to the left? Zn2+(aq) + 4OH-(aq) ⇌ Zn(OH)42-(aq) Choose only ONE best answer. A Addition of Zn2+ B Removal of Zn(OH)42- C Lowering the pH D Addition of OH- E None of these

Lowering the pH Lowering the pH means making the solution more acidic and a more acidic solution will have a reduction in the concentration of OH-. A reduction in the concentration of OH- (a reactant) will indeed result in the shift to the left and is the correct answer.

Can Kc be negative?

No

Do solids and liquids show up in the equilibrium constant expression?

No

When Rate f=Rate r, do the concentrations change?

No

2C(s)+O2(g)<-->2CO(g)+Heat What will be the result in an increase of C?

No shift because not a stress

H2(g)+Cl2(g)<-->2HCl(g) Keq=16 What would result from an increase in H2?

No shift to Kc value

Which of the following changes to the following reaction at equilibrium would result in a shift to the left? CaCO3(s) ⇌ Ca2+(aq) + CO32-(aq) Choose only ONE best answer. A Addition of CaCO3 B Removal of CaCO3 C Removal of Ca2+ D Removal of CO32- E None of these

None of these

Which of the following changes to the following reaction at equilibrium would result in a shift to the right? COCl2(g) + HCl(g) ⇌ CHCl3(l) + ½O2(g) Choose only ONE best answer. A An increase in the volume of the reaction vessel B A decrease in pressure C Addition of O2 D Removal of COCl2 E None of these

None of these

What is the equilibrium constant expression for the following reaction? N2O4(g) → 2NO2(g)

P[NO2]^2/P[N2O4]

Which of the following changes to the following reaction at equilibrium would result in a shift to the right? 2Tl(s) + Co2+(aq) ⇌ 2Tl+(aq) + Co(s) Choose only ONE best answer. A Addition of Tl B Removal of Tl+ C Addition of Tl+ D Removal of Co2+ E Addition of Co

Removal of Tl+

H2(g)+Cl2(g)<-->2HCl(g) Keq=16 If 2 mols of both H2 and Cl2 are each placed in a 2L vessel, what will be the equilibrium concentrations of H2, Cl2, and HCl?

SQR 16=SQR [(2X^2)/(1-X)^2 (1-X)4=2X X=2/3 H2: 1-(2/3)= .33 Cl2: 1-(2/3)= .33 HCl: 2(2/3)=1.33

If the reaction is endothermic (positive), what will an increase in temperature cause?

Shift to right

2C(s)+O2(g)<-->2CO(g)+Heat What will be the result of increasing pressure by decreasing volume?

Shifts left because there are less moles of O2 than CO therefore more volume If there were an equal number of mols, there would be no shift

What is the result when Q<K

Shifts right

2C(s)+O2(g)<-->2CO(g)+Heat What will be the result in an increase of O2?

Shifts right to use up O2 and make more products?

2C(s)+O2(g)<-->2CO(g)+Heat What will be the result in a decrease of CO?

Shifts to right because O2 and C will make more products

For the following reaction Kc = 2.2 x 10-9 HOBr(aq) ⇌ H+(aq) + BrO-(aq) If [H+] = 2.2 x 10-5M, [BrO-] = 1 x 10-5M and [HOBr] = 0.1M then which of the following is true? Choose only ONE best answer. A The reaction is at equilibrium. B The reaction must proceed to the left to reach equilibrium. C The reaction must proceed to the right to reach equilibrium. D The forward rate is faster than the reverse rate. E Not enough info is given to determine whether the reaction is at equilibrium or not.

The reaction is at equilibrium.

For the following reaction Kc = 1.7 x 107 Ag+(aq) + 2NH3(aq) ⇌ Ag(NH3)2+(aq) If [Ag+] = 1 x 10-3M, [NH3] = 3 x 10-2M and [Ag(NH3)2+] = 0.9M then which of the following is true? Choose only ONE best answer. A The reaction is at equilibrium. B The reaction must proceed to the left to reach equilibrium. C The reaction must proceed to the right to reach equilibrium. D The reverse rate is faster than the forward rate. E Not enough info is given to determine whether the reaction is at equilibrium or not.

The reaction must proceed to the right to reach equilibrium.

For the following reaction Kc = 2.9 x 1015 Zn2+(aq) + 4OH-(aq) ⇌ Zn(OH)42-(aq) If [Zn2+] = 4 x 10-4M, [OH-] = 1 x 10-2M and [Zn(OH)42-] = 0.2M then which of the following is true? Choose only ONE best answer. A The reaction is at equilibrium. B The reaction must proceed to the left to reach equilibrium. C The reaction must proceed to the right to reach equilibrium. D The reverse rate is faster than the forward rate. E Not enough info is given to determine whether the reaction is at equilibrium or not.

The reaction must proceed to the right to reach equilibrium.

What will be the result of increasing the pressure (by reducing the volume) on the following system at equilibrium? 2Sb(s) + 3COCl2(g) ⇌ 2SbCl3(g) + 3CO(g) Choose only ONE best answer. A The reaction will proceed to the left as there are fewer moles of gas on the reactants' side. B The reaction will proceed to the left as there are more moles of gas on the reactants' side. C The reaction will proceed to the right as there are fewer moles of gas on the products' side. D The reaction will proceed to the right as there are more moles of gas on the products' side. E There won't be a shift as there are the same number of moles of reactants as products.

The reaction will proceed to the left as there are fewer moles of gas on the reactants' side.

2C(s)+O2(g)<-->2CO(g)+Heat What is the Kc?

[CO]^2/[O2]

What is the equilibrium constant expression for the following reaction? 2HF(aq) + H2NCH2CH2NH2(aq) → H3NCH2CH2NH32+(aq) + 2F-(aq)

[H3NCH2CH2NH32+][F-]^2/[HF]^2[H2NCH2CH2NH2]

What is the equilibrium constant expression for the following reaction? 2NH3(g) → N2(g) + 3H2(g)

[N2][H2]^3/[NH3]^2

Which of the following is false for the following reaction at equilibrium? A(aq) → B(aq) Kc = 2.8 x 10-5 Choose only ONE best answer. A [A] > [B] B kforward = kreverse C Δ[reactants] / Δt = 0 D Δ[products] / Δt = 0 E [B] / [A] = 2.8 x 10-5

kforward = kreverse