Unit 1 Test 2

PrePublic Review #2

Name:______________

1. Which predicts how chemical equilibria respond to changes in temperature? (A) Arrhenius theory (B) First Law of Thermodynamics (C) Hess’s Law (D) Le Châtelier’s Principle 2. Which would result in the highest concentration of ammonia for the equilibrium below?

(A) (B) (C) (D)

N2(g) + 3 H2(g) ⇌ 2 NH3(g) + energy decreasing the temperature and decreasing the pressure decreasing the temperature and increasing the pressure increasing the temperature and decreasing the pressure increasing the temperature and increasing the pressure

3. Which would cause an increase in the value of Keq for the equilibrium below? 2 HCl (g) + F2 (g) ⇌ 2 HF (g) + Cl2 (g) (A) decreasing temperature (B) increasing temperature (C) decreasing volume (D) increasing volume

ΔH = -74.8 kJ

4. SO2(g) and O2(g) are introduced into an evacuated flask and an equilibrium is established. 2 SO2(g) + O2(g)

⇌

2 SO3 (g)

What is true given the equilibrium concentrations below? [SO2] = 1.5 mol/L

[O2] = 3.00 mol/L

[SO3] = 4.50 mol/L

(A) Keq > 1 (B) Keq < 1 (C) Keq decreases when SO2(g) is added to the equilibrium mixture. (D) Keq increases when SO2(g) is added to the equilibrium mixture.

5. What is the equilibrium concentration of N2(g), given the reaction and equilibrium concentrations below? 2 NO2 (g) ⇌ N2(g) + 2 O2(g) [O2(g)] = 10.0 mol/L (A) 0.0025 mol/L (B) 0.0050 mol/L (C) 0.020 mol/L (D) 0.040 mol/L

[NO2(g)] = 5.0 mol/L

Keq = 1.0 × 10-2

6. Which are equal in a dynamic equilibrium? (A) activation energy of the forward and reverse reactions are equal (B) concentration of reactants and products are equal (C) moles of reactants and products are equal (D) rate of the forward and reverse reactions are equal 7. Which will affect the value of Keq? (A) adding a catalyst (B) adding reactants (C) decreasing temperature (D) decreasing volume 8. When the concentration of A is increased in the equilibrium below, it takes 100 minutes to reestablish the equilibrium. Which best describes the equilibrium system 60 minutes after substance A was added? A⇌B (A) (B) (C) (D)

[A] > [B] [A] < [B] forward rate > reverse rate forward rate < reverse rate

9. What is the equilibrium expression for the following system? 4 Fe(s) + 3 O2(g) ⇌ 2 Fe2O3(s)

10. Which will cause the equilibrium below to shift to the right? CH3Cl(aq) + OH-(aq) (A) (B) (C) (D)

adding KCl adding NaOH removing CH3Cl removing OH-

⇌

CH3OH(aq) + Cl-(aq)

11. Given the equilibrium concentrations below, calculate the value of Keq for: N2(g) + O2(g) [N2(g)] = 0.10 mol/L (A) (B) (C) (D)

⇌

2NO(g)

[O2(g)] = 0.20 mol/L

[NO(g)] = 0.0030 mol/L

2.2×10−4 4.5×10−4 1.5×10−1 3.0×10−1

12. The equilibrium system below is in a test tube at room temperature. When five drops of Fe(NO3)3(aq) is added, a precipitate forms.

⇌

H+(aq) + 2 CrO42-(aq) yellow

Cr2O7 2-(aq) + OH-(aq) orange

What is the colour of the solution and how does the concentration of OH-(aq) change? colour (A) (B) (C) (D)

orange orange yellow yellow

[OH)(aq)] decrease increase decrease increase

13. What happens to [O2(g)] and [H2O(g)] in the equilibrium below if the system is heated? 4 HCl(aq) + O2(g) [O2(g)] (A) (B) (C) (D)

decreases decreases increases increases

⇌

2 H2O(g) + 2 Cl2(g)

ΔH = +113 kJ

[H2O(g)] decreases increases decreases increases

14. Use the equilibrium concentrations provided to calculate Keq for the equilibrium below: [CO(g)] = 0.105 mol/L , [H2(g)] = 0.250 mol/L, and [CH3OH(g)] = 0.00261 mol/L, CO(g) + 2 H2(g) (A) 0.0994 (B) 0.398 (C) 2.51 (D) 10.0

⇌

CH3OH(g)

15. What happens to the equilibrium below when NO(g) is added to the system? 2 NO(g) + Cl2(g) Shift (A) (B) (C) (D)

left left right right

⇌

2 NOCl(g)

[Cl2(g)] decreases increases decreases increases

16. Which is necessary for an equilibrium to exist? (A) closed system and changing temperature (B) closed system and constant temperature (C) open system and changing temperature (D) open system and constant temperature 17. Which change will increase the concentration of F2(g) in the equilibrium below? 2 HCl(g) + F2(g) (A) (B) (C) (D)

⇌

2 HF(g) + Cl2(g)

ΔH = -74.8 kJ

decrease in pressure decrease in temperature increase in pressure increase in temperature

18. Which change in the equilibrium below would result in the highest concentration of Cl2(g)? PCl3(g) + Cl2(g)

⇌

PCl5(g)

ΔH = -84.2 kJ

(A) decreasing temperature (B) decreasing volume (C) increasing [PCl3] (D) increasing [PCl5]

Extended Response 19. Initially 4.00 mol of HCl(g) and 4.00 mol of O2(g) were placed in a 2.00 L vessel and allowed to establish equilibrium. At equilibrium the vessel contained 0.500 mol of Cl2(g). Calculate Keq? 2 HCl(g) + O2(g)

⇌

H2O2(g) + Cl2(g)

20. 1.0 mol each of SO2(g) and O2(g) are placed in a 1.0 L reaction vessel and allowed to reach equilibrium. The concentrations of the reactants and products after various time periods are shown in the data table below. 2 SO2(g) + O2(g) Time (min.) 0.0 1.0 2.0 3.0 4.0 5.0 6.0

⇌

2 SO3(g)

[SO2] mol/L 1.00 0.86 0.76 0.68 0.64 0.64 0.64

[O2] mol/L 1.00 0.93 0.88 0.84 0.82 0.82 0.82

[SO3] mol/L 0.00 0.14 0.24 0.32 0.36 0.36 0.36

(a) When was equilibrium established? Justify your answer.

(b) Compare the forward and reverse reaction rates at 2.0 minutes? Explain your answer.

21. The system below is initially at equilibrium. HCHO(g)

⇌

CO(g) + H2(g)

ΔH = +5.26 kJ

(a) Explain how a decrease in temperature will affect [H2(g)]?

(b) Explain how increasing the volume of the reaction vessel will affect [HCHO(g)]?

22. The equilibrium constant expression for a reaction is:

(a) What is the equation for this equilibrium?

(b) A 1.0 L flask was contains 2.0 × 10-2 mol of H2O(g), 3.0 × 10-2 mol of Cl2O(g), and 4.0 × 10-3 mol of HOCl(g). Is the system at equilibrium? Justify your answer.

23. The equilibrium concentrations for 3 H2(g) + N2(g) ⇌ 2 NH3(g) are graphed below. More H2(g) is added to the system at time t1. Extend the graph to show how the concentrations of N2(g), H2(g) and NH3(g) will change until a new equilibrium is established.