Question

Chemical Equilibrium Pre and Post Lab Questions 1. Which is true for the following reaction? N2 (g) + 3H2 (g) -----> 2NH3 (g) + heat a. For the reverse reaction, ΔH is negative. b. For the reverse reaction, ΔH is negative. c. All of the above. d. None of the above. Consider the following equilibrium when answering questions 2 to 6. N2O4 (g) ------> 2 NO2 (g) ΔH = 56.9 kJ 2 . Which of the following is true about reaction when an amount of NO2 (g) is added to the equilibrium reaction? a. Equilibrium will shift to consume N2O4 (g). b. Equilibrium will shift to produce more NO2 (g). c. Equilibrium will shift to consume the NO2 (g). d. No effect on the equilibrium. 3. Which of the following is true about reaction when the pressure is lowered by increasing the volume of the reaction container. a. Equilibrium will produce more N2O4 (g) to offset the pressure drop. b. Equilibrium will shift to the right to produce more NO2 (g). c . Equilibrium will shift to consume more NO2 (g). d. No effect on the equilibrium. 4. Which of the following is true about reaction when the temperature is raised? a. Equilibrium will shift to the left. b. Equilibrium will shift to the right. c. Equilibrium will shift to produce more heat. d. No effect on the equilibrium. 5. Which of the following is true about reaction when a catalyst is added to the system? a. Equilibrium will shift to the left. b. Equilibrium will shift to the right. c. Equilibrium will shift to lower the heat. d. No effect on the equilibrium. 6. Which of the following will increase the Keq of the equilibrium in reaction ? a. Add NO2 (g). b. Heat the reaction container. c. Put the reaction container in ice. d. Add a catalyst. Consider the following equilibrium when answering questions 7 and 8. CO (g) + 3 H2 (g) ---------> CH4 (g) + H2O (g) 7. Which of the following is true about reaction when the concentration of CO is increased? a. Equilibrium will shift to the left. b. Equilibrium will shift to the right. c. No effect on the equilibrium. D Equilibrium constant will increase. 8. Which of the following is true about reaction when the concentration of CH4 (g) is increased? a. Equilibrium will shift to the left. b. Equilibrium will shift to the right. c. No effect on the equilibrium. d. Equilibrium constant will decrease. Consider the following equilibrium when answering questions 9 and 11. 2C2H2 (g) + 5 O2 (g) ---------> 4 CO2 (g) + 2 H2O (g) + heat 9. Which of the following is true about reaction when the concentration of O2 (g) is decreased? a. Equilibrium will shift to the left. b. Equilibrium will shift to the right. c. No effect on the equilibrium. d. Equilibrium constant will decrease. 10. Which of the following is true about reaction when the temperature is increased? a. Equilibrium will shift to the left. b. Equilibrium will shift to the right. c. No effect on the equilibrium. d. No effect on the equilibrium constant. 11. Which of the following is true about reaction when the pressure is increased by decreasing the volume of the reaction container? a. Equilibrium will shift to the left. b. Equilibrium will shift to the right. c. No effect on the equilibrium. d. No effect on the heat produced. Consider the following equilibrium when answering questions 12 and 17. 2 H2O (g) + 2 Cl2 (g) + heat ----------> 4 HCl (g) + O2 (g) 12. Which of the following is true about reaction when the reaction mixture is heated. a. Equilibrium will shift to the left. b. Equilibrium will shift to the right. c. No effect on the equilibrium. d. No effect on the equilibrium constant. 13. Which of the following is true about reaction when O2 (g) is added to the mixture. a. Equilibrium will shift to the left. b. Equilibrium will shift to the right. c. No effect on the equilibrium. d. Equilibrium constant will decrease. 14. Which of the following is true about reaction when the pressure is increased by the addition of an inert gas? a. Equilibrium will shift to the left. b. Equilibrium will shift to the right. c. No effect on the equilibrium. d. Equilibrium constant will decrease. 15. Which of the following is true about reaction when the size of the reaction container is increased? a. Equilibrium will shift to the left. b. Equilibrium will shift to the right. c. No effect on the equilibrium. d. Equilibrium constant will increase. 16. Consider the reaction N2 (g) + O2 (g) ---------> 2 NO (g) + heat The product is favored a. When the reaction temperature is increased. b. When the volume of the reaction container is reduced. c. When He (g) is added to the reaction. d. When the reaction temperature is lowered. 17. When the temperature of an equilibrium system for the following reaction is increased, CO (g) + H2O (g) --------> CO2 (g) + H2 (g) the reaction shifts to the left. Which of the following is true? a. Equilibrium is exothermic. b. Equilibrium is endothermic. c. None of the above. d. All of the above

Answer 1

1) The given reaction is

N₂ + 3 H₂ -------> 2 NH₃ + heat

Heat is a product of the reaction, i.e, the reaction releases heat into the surroundings. Hence, ΔH for the forward reaction (formation of NH₃ from N₂ and H₂) has negative value and consequently, the reverse reaction (decomposition of NH₃ to form N₂ and H₂) has positive ΔH (ans).

I explained the answer; however choices (a) and (b) are both same. Kindly check the question and choose the correct option.

2) The equilibrium reaction is

N₂O₄<======> 2 NO₂ ; ΔH = 56.9 kJ

The equilibrium constant is

K = [NO₂]²/[N₂O₄]

K remains constant at a particular temperature.

When excess NO₂ is added, [NO₂] increases and hence [N₂O₄] must increase to keep K constant. This is possible only when the equilibrium shifts in the reverse direction, producing more N₂O_4.

Therefore, (c) is the correct statement.

3) Assume ideal behavior of the gases. The pressure of an ideal gas is inversely proportional to the volume. Again, as per the gas law, the volume of an ideal gas is directly proportional to the number of moles of the gas. Therefore, the higher the number of moles of gases, the higher is the volume and consequently, the lower is the pressure.

When the pressure is lowered, the equilibrium will shift in the direction where the number of moles of gases is more. Since the forward reaction proceeds with an increase in the number of moles of gaseous products, hence the equilibrium shifts to the right. Therefore, statement (b) is correct.

4) The enthalpy change for the reaction is positive. Hence the reaction is endothermic. Endothermic reactions are favored by high temperatures, hence the equilibrium shifts to the right, producing more NO₂. Thus, statement (b) is correct.

5) A catalyst alters the rate of both the forward and the reverse reactions, but keeps the position of the equilibrium unchanged. Hence, a reaction at equilibrium is unaffected by the addition of a catalyst. Statement (d) captures the correct essence.

6) The equilibrium constant, K_eq depends only on the temperature of the system. Any effect that aims to change the temperature of the system will alter the value of K_eq. Since statements (b) and (c) both describe a change in temperature (b increases the temperature while c reduces the temperature). Hence, both the processes will change the value of K_eq. Therefore, both (b) and (c) are correct.