Ch 13. Equilibrium concepts HW

4. The Kc for the formation of HI from iodine and hydrogen gas is 54. If the concentrations of HI, I2, and H2 are 5.338 M, 0.112 M, and 0.198 M respectively, which statement is correct? H2 +I2 ⇌ 2HI A. Q = 5.15 which is less than Kc, therefore the reaction needs to proceed towards the right to reach equilibrium B. Q = 15.2 which is less than Kc, therefore the reaction needs to proceed towards the right to reach equilibrium C. Q = 1284 which is more than Kc, therefore the reaction needs to proceed towards the left to reach equilibrium

*C. Q = 1285 which is more than Kc, therefore the reaction needs to proceed towards the left to reach equilibrium

What does ICE stand for?

-Initial consumption -Change -Equilibrium

A 0.72-mol sample of PCl5 is put into a 1.00-L vessel and heated. At equilibrium, the vessel contains 0.40 mol of PCl3(g) and 0.40 mol of Cl2(g). Calculate the value of the equilibrium constant for the decomposition of PCl5 to PCl3 and Cl2 at this temperature. PCl5(g) ⇌ PCl3(g) + Cl2(g)

A. 0.5

16.Changes in volume may or may not affect gas-phase systems at equilibrium. Explain how to recognize the conditions under which changes in volume will affect gas-phase systems at equilibrium A. An effect arises only when the number of moles of gaseous reactants in the equation differs from the number of moles of gaseous products. B. As the volume of a gaseous system decreases, the gases become compressed, producing greater molar concentrations. This change in concentration represents a stress on the system, and the system will act to remove the stress, shifting the equilibrium to the side with the more number of moles. C. An effect arises only when the number of moles of gaseous reactants in the equation is the same as the number of moles of gaseous productsA.

A. An effect arises only when the number of moles of gaseous reactants in the equation differs from the number of moles of gaseous products. **If the total number of moles of gas is the same on both sides of the equation (Δng = 0), compression or expansion will have no effect on the equilibrium.

11. The initial concentrations or pressures of reactants and products are given for the following system. Calculate the reaction quotient and determine the direction in which each system will proceed to reach equilibrium. 2NH3 (g) ⇌ N2(g) + 3H2 (g), Kc =17; [NH3] = 0.50 M, [N2] = 0.15 M, [H2] = 0.12 M A. Qc= 1.0 X 10-3 , proceeds right B. Qc= 1.0 X 103 , proceeds left A. Qc= 1.0 X 10-2 , proceeds right

A. Qc= 1.0 X 10-3 , proceeds right

2.Consider the following equilibrium mixture in a closed system: H2O(g) + CO(g) ⇌ H2(g) + CO2(g). Explain what would happen to the equilibrium upon the addition of hydrogen gas?

A. The addition of hydrogen gas would disrupt the equilibrium causing it to shift towards the left until new equilibrium is achieved.

14. Convert the values of Kc to values of KP. KP = Kc(RT)Δn Cl2(g) + Br2 (g) ⇌ 2BrCl(g) Kc = 4.7 x10-2 at 25 *C A. Δn = (2) - (1 + 1) = 0, KP = Kc(RT)0 = Kc = 4.7 × 10-2 B. Δn = (2) - (1) = 1, KP = Kc(RT)1 = 4.7 × 10-2 (0.08206 298.15) = 1.2 C. Δn = (1) - (1 + 1) = -1, KP = Kc(RT)-1 = 4.7 × 10-2 (0.08206 298.15) -1 = 1.9 × 10-3

A. Δn = (2) - (1 + 1) = 0, KP = Kc(RT)0 = Kc = 4.7 × 10-2 Δn = Needs to be 0 in for Kp = Kc

7. Write the mathematical expression for the reaction quotient, Qc, for the following reaction: CH4(g) + Cl2 (g) ⇌ CH3Cl (g) + HCl (g)

A. 𝑄𝑐=[𝐶𝐻3𝐶𝑙][𝐻𝐶𝑙]/[𝐶𝐻4][𝐶𝑙2]

1.What does it mean to describe a reaction as "reversible"? A. The reaction can proceed in both the forward and reverse directions B. The reaction can proceed in the forward direction, not reverse direction. C. The reaction can not proceed in the forward direction, but can proceed in the reverse direction.

A.The reaction can proceed in both the forward and reverse directions

17.necessary step in the manufacture of sulfuric acid is the formation of sulfur trioxide SO3, from sulfur dioxide, SO2, and oxygen, O2 shown here. SO2 (g) + O2 (g) ⇌ SO3 (g) At high temperatures, the equilibrium amount (concentration or partial pressure) of SO3 is lower than it would be at lower temperatures. Does the equilibrium constant for the reaction increase, decrease, or remain about the same as the temperature increases? Is the reaction endothermic or exothermic- A. The equilibrium constant decreases as the temperature increase as less product is collected at higher temperature. The reaction is exothermic. B. The equilibrium constant decreases as the temperature increase as less product is collected at higher temperature. The reaction is endothermic. C. The equilibrium constant increases as the temperature increase. The reaction is exothermic.

Answer A. The equilibrium constant decreases as the temperature increase as less product is collected at higher temperature. The reaction is exothermic. a. The equilibrium constant for this reaction decreases as the temperature increases since K is the square of the amount(concentration or partial pressure) of SO3 over the product of the square of SO2 and the amount of O2. When the temperature decreases, the amount of produced SO3 also decreases, making the K smaller. b. This reaction is exothermic because the reaction moves toward the reactant as the temperature increases. According to Le Chatlier's Principle, the reaction goes to the direction which could "cancel" this increase in temperature, meaning that it moves to the direction which "absorbs" the increased temperature, or in other words, the endothermic direction. Since the reaction is endothermic when moving to the reactants, it is exothermic when moving toward the products.

5. Among the solubility rules: All chlorides are soluble except Hg2Cl2, AgCl, PbCl2, and CuCl.Write the expression for the equilibrium constant for the reaction represented by the equation. Ag+ (aq) + Cl- (aq) -->AgCl(s). Is Kc > 1, < 1, or ≈ 1?

B. 1 [Ag+][Cl−], Kc > 1

21. Calculate the value of the equilibrium constant KP for the reaction 2NO (g) + Cl2 (g) ⇌ 2NOCl (g) from these equilibrium pressures: NO, 0.050 atm; Cl2, 0.30 atm; NOCl, 1.2 atm. A. 1.9 x 102 B. 1.9 x 103 C. 1.5 x 102 D. 1.5 x 103

B. 1.9 x 103

22.A sample of ammonium chloride was heated in a closed container. NH4 Cl(s) ⇌ NH3(g) + HCl (g) At equilibrium, the pressure of NH3(g) was found to be 1.75 atm. What is the value of the equilibrium constant KP for the decomposition at this temperature A. 0.1256 B. 3.06 C. 0.0306 D. 0.01256

B. 3.06

28. Calculate the equilibrium constant at 25C for the following reaction from the value of ΔG given. 2 2 I ( ) Br ( ) 2IBr( ) 7.3 kJ s l g GA. K = 0.53B. K = 0.053C. K = 0.0053SEE HOMEWORK

B. K = 0.053

3. Write the equilibrium expression for 2NO(g) + 2H2(g) ⇌ N2(g) + 2H2O(g). A. Kc = [NO]2 [H2]2 /[H2O]2 [𝑁2] B. Kc = [H2O]2 [𝑁2]/ [NO]2 [H2]2 C. Kc = [𝑁2] [NO]2 /[H2]2

B. Kc = [H2O]2 [𝑁2]/ [NO]2 [H2]2

12. The initial concentrations or pressures of reactants and products are given for the following system. Calculate the reaction quotient and determine the direction in which each system will proceed to reach equilibrium. 2SO3 (g) ⇌ 2SO2(g) + 3O2 (g), KP=6.5; SO2 = 1.00 atm, O2 = 1.130 atm, SO3 = 0 atm A. Qc= infinitely large , proceeds right B. Qc= infinitely large , proceeds left C. Qc= 1.13, proceeds right

B. Qc= infinitely large , proceeds left

24. Assume that the change in concentration of N2O4 is small enough to be neglected in the following problem. Calculate the equilibrium concentration of NO2 in 1.00 L of a solution prepared from 0.129 mol of N2O4 with chloroform as the solvent. N2O4 (g) ⇌ 2NO2 (g) Kc = 1.07 x 10-5 in chloroformA. [NO2] = 5.87 10-4MB. [NO2] = 1.17 10-3 MC. [NO2] = 0.128 M

B. [NO2] = 1.17 10-3 M

30. Calculate ΔG for the following reaction from the equilibrium constant at the temperature given. 2SO2 (g) + O2 (g) 2SO3 (g) T=500OC KP =48.2A. ΔG° = 24.9 kJ;B. ΔG° = -24.9 kJC. ΔG° = 14.9 kJD. ΔG° = -14.9 kJ

B. ΔG° = -24.9 kJ

15. Write the expression of the reaction quotient for the ionization of HOCN in water H2O(l) + HOCN(aq) ⇌ H3O+ (aq) + OCN- (aq)

B. 𝑄𝑐 =[𝐻3𝑂+] [𝑂𝐶𝑁−]/[𝐻𝑂𝐶𝑁]

9. Write the mathematical expression for the reaction quotient, Qc, for the following reaction: CH4(g) + 2O2 (g) ⇌ CO2 (g) + 2H2O (l)

B. 𝑄𝑐=[𝐶𝑂2] /[𝐶𝐻4][𝑂2]2

13.For which of the following reactions does Kc (calculated using concentrations) equal KP ? (1) MgSO47H2O(s) ⇌ MgSO4 (s) + 7H2O (g) (2) CH4(g) + 2O2 (g) ⇌ CO2 (g) + 2H2O (g) (3) CH4(g) + Br2 (l) ⇌ CH3Cl (g) + HCl (g) (4) N2(g) + O2 (g) ⇌ 2NO (g) (5) P4(s) + 5O2 (g) ⇌ P4O10 (s) A. (3) and (4) B. (1), (2), and (5) C. (2) and (4)

C. (2) and (4)

25. Assume that the change in pressure of H2S is small enough to be neglected in the following problem. Calculate the equilibrium pressures of S2 in an equilibrium mixture that results from the decomposition of H2S with an initial pressure of 0.824 atm. 2H2S (g) ⇌ S2(g) + 2H2 (g) KP = 2.2 x 10-6A. 0.810 atmB. 0.014 atmC. 0.0072 atm

C. 0.0072 atm

26. What is the concentration of HClO after a mixture that contains [H2O] = 2.00 M and [Cl2O] = 2.00 M comes to equilibrium at 25 C? H2O(g) + Cl2O(g) ⇌ 2HClO(g) Kc = 0.0900A. 0.153 MB. 0.307 MC. 0.522 M

C. 0.522 M

20. How will an increase in temperature affect each of the following equilibrium? How will a decrease in the volume of the reaction vessel affect it? N2(g) + O2 (g) ⇌ 2NO (g) , ΔH= 181 kJ A. An increase in temperature will shift the equilibrium to the left; a decrease in the volume of the reaction vessel will shift the equilibrium to the right. B. An increase in temperature will shift the equilibrium to the right; a decrease in the volume of the reaction vessel will shift the equilibrium to the right. C. An increase in temperature will shift the equilibrium to the right; a decrease in the volume of the reaction vessel will not affect the equilibrium.

C. An increase in temperature will shift the equilibrium to the right; a decrease in the volume of the reaction vessel will not affect the equilibrium. Changing the temperature of a system results in a change in the value of the equilibrium constant K: -If the forward reaction is exothermic, then K decreases as T increases. -If the forward reaction is endothermic then K increases as T increases. If you increase the temperature you add the heat. The equilibrium responds in a fashion that consumes the added heat.

27. Calculate the equilibrium constant at 25C for the following reaction from the value of ΔG given. O ( ) 2F ( ) 2OF ( ) - 9.2 kJ 2 2 2 g g g GA. K = 21B. K = 31C. K = 41SEE HOMEWORK

C. K = 41

19. Methanol can be prepared from carbon monoxide and hydrogen at high temperature and pressure in the presence of a suitable catalyst. 2H2(g) + CO (g) ⇌ CH3 OH(g) ΔH=-90.2 kJ What will happen to the concentrations of H2, CO, and CH3OH at equilibrium if CO is removed? A. [H2] decreases, [CO] decreases, [CH3OH] increases B. [H2] increases, [CO] decreases, [CH3OH] increases C. [H2] increases, [CO] decreases, [CH3OH] decreases

C. [H2] increases, [CO] decreases, [CH3OH] decreases

10. Which of the systems described below are homogeneous equilibria? Which are heterogeneous equilibria? (1) CuSO45H2O(s) ⇌ CuSO4 (s) + 5H2O (g) (2) CH4(g) + 2O2 (g) ⇌ CO2 (g) + 2H2O (l) (3) CH4(g) + Cl2 (g) ⇌ CH3Cl (g) + HCl (g) (4) N2(g) + O2 (g) ⇌ 2NO (g) (5) P4(s) + 5O2 (g) ⇌ P4O10 (s)

C. homogenous: (3), and (4); heterogeneous: (1), (2) and (5)

29. Calculate ΔG for the following reaction from the equilibrium constant at the temperature given. 2 Cl ( ) Br ( ) 2BrCl( ) T 25 C 4.7 10 2 2 g g g KPA. ΔG° = -4.6 kJ;B. ΔG° = -5.6 kJC. ΔG° = 7.6 kJ

C. ΔG° = 7.6 kJ

8. Write the mathematical expression for the reaction quotient, Qc, for the following reaction: P4(s) + 5O2 (g) ⇌ P4O10 (s)

C. 𝑄𝑐=1[𝑂2]5

6. Among the solubility rules: All chlorides are soluble except Hg2Cl2, AgCl, PbCl2, and CuCl.Write the expression for the equilibrium constant for the reaction represented by the equation PbCl2(s) -->Pb2+ (aq) + 2Cl- (aq). Is Kc > 1, < 1, or ≈ 1?

D. [𝑃𝑏2+][Cl−] 2, Kc < 1

18.Suggest ways in which the concentration of hydrazine, N2H4, could be increased in an equilibrium described by the following equation: N2(g) + 2H2 (g) ⇌ N2H4 (g) ΔH=95 kJ. A. Add N2; B. Add H2; C. Decrease the container volume D. Heat the mixture E. All of the above

E. All of the above

When pressure increases, what happens to the number of moles?

moles decrease

What formula do you usually need to use when you're using ICE, unless there is an "assumption" that one of the products or reactants is too small

quadratic

If 0 is in the denominator in chemistry, what does this mean?

that the quotient is infinitely large