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Chemical Equilibrium MCQs and Answers with explanation

Chemical Equilibrium MCQs and Answers with explanation

1. Kc is independent of





... Answer is b)
Explanation: Kc is the ratio of concentration of products to concentration of reactants. In endothermic reactions, heat is involved in reactant side (i.e., Reactant + heat .......> Product) and in exothermic reaction, heat is involved in product side (i.e., Reactant .......> Product + heat) . If we increase the temperture, endothermic reaction will move in forward direction with increase in concentration of products and exothermic reaction will move in reverse direction with increase in concentration of reactants to re-establish the equilibrium. As a result, concentration of reactant and product will be changed. Hence, Kc will become larger in endothermic reaction and smaller in exothermic reaction. All reversible chemical reactions are either endothermic or exothermic, so, Kc is temperatrue dependant. However, Kc is independent of pressure and related to Kp as follows Kp = Kc(RT)Δn. or Kc = Kp(RT)-Δn. Consider a chemical reaction where number of moles of reactants and products are equal, When we increase the pressure, volume of each reactant and product decreases which result in increase in their partial pressures both in numerator and denominator. Overall, Kp remains constant. However, if the number of moles of product are less than the number of moles of reactant, for example,
, Kp = (PC)(PD) / (PA)2(PB) where PA,PB, PC and PD are partial pressures of A, B, C and D, respectively. Kp = (PXC)(PXD) / (PXA)2(PXB) Kp = (P)2(XC)(XD) / (P)3(XA)2(XB) Kp = (XC)(XD) / (P)(XA)2(XB) Where P = total pressure. As we increase the pressure, the value of term 'P' increases in denomenator. In order to compensate this, reactions will move in forward direction, and partial pressures of reactants in denomenator will be decreased and partial pressures of products in numerator will be increased and ultimatly, Kp value remains undchanged. As a result Kc also remains constant.

2. For which of the following reactions, Kc has no units of concentration


... Answer is b)
Explanation:


 

3. For the following reaction 





... Answer is c)
Explanation: For this reaction, Kp = Kc(RT)Δn Where Δn = number of moles of product - number of moles of reactant Kp = Kc(RT)3-3 Kp = Kc(RT)0 Kp = Kc Kp - Kc = 0

4. What is the effect of addition of catalyst on an equilibrium mixture?





... Answer is d)
Explanation: Catalyst has no effect on chemical equilibrium mixture, however, it increases the rates of both forward and reverse reactions equally, and chemical equilibrium is established very quickly.

5. If Ksp = [M+2]3[X-3]2, the chemical formula of compound is





... Answer is c)
Explanation: Ksp expression shows the concentrations of ions each raised to a power equal to its number of ions in the formula unit of the compound. It means there are thee ions of M+2 and two ions of X-3 in the formula unit. So formula unit is M3X2.

6. NaCl can be purified by passing HCl gas through the -----solution of NaCl.





... Answer is b)
Explanation: NaCl is purified on the basis of common ion effect. Purification of NaCl is only possible when NaCl is in equilibrium with its ions which is only possible in concentrated solution of NaCl. On passing HCl, reaction moves in reverse direction to re-establish equilibrium. As a result the solubility of NaCl is decreased due to common ion effect of Cl and it is precipitated out.

7. Kc = Kp when Δn is equal to





... Answer is a)
Explanation: Kp = Kc(RT)Δn. When Δn = 0 Kp = Kc(RT)0. Kp = Kc(1) = Kc as (RT)0 = 1

8. Consider the following reaction 


 Yield of sulphur trioxide can be increased by

a) Increasing pressure 
b) Increasing temperature 
c) Adding catalyst 
d) Increasing concentration of oxygen




... Answer is 4)
Explanation: According to Le-Chatleir principle, yield of sulphur trioxide can be increases by increasing the pressure as equilibrium moves in the direction of lower number of moles(i.e., product). Yield can also be increased by increasing the concentration of Oxygen. Some Additional MCQs

9. Units of Kc for the following reaction 





... Answer is b)
Explanation:

.

10. Which of the following statement is true about equilibrium state





... Answer is d)
Explanation: Concentrations of reactants and products become constant at equilibrium state.

11. Law of mass action was proposed by Guldberg and Waag in





... Answer is d)
Explanation: Law of mass action was proposed by Guldberg and Waag in 1864.

12. When 50% of reactants are converted into a products in a reversible reaction, the value of equilibrium constant(Kc) is





... Answer is d)
Explanation: The value of equilibrium concentration is constant for a particular reaction at constant temperature and it is independent of concentration of reactant and product.

13. The value of equilibrium constant (Kc) for the reaction 

is 10-13 at 2000 C. Calculate the value of Kp for this reaction





... Answer is b)
Explanation: Kp = Kc(RT)Δn. When Δn = no. of moles of product- no. of moles of reactant Δn = 2- 2 =0 Kp = Kc(RT)0. Kp = Kc(1) = Kc as (RT)0 = 1 Kp = 10-13

14. For the reaction 






... Answer is b)
Explanation: Kp = Kc(RT)Δn. When Δn = no. of moles of product- no. of moles of reactant Δn = 2- 1 =1 Kp = Kc(RT)1. Kp = Kc(RT) It means Kp is RT times greater than Kc, So, Kp>Kc

15. For an exothermic reaction, increase in temperature will favor the





... Answer is b)
Explanation: In exothermic reaction heat is involved in product side. Therefore when we increase the temperature the reaction will move in reverse direction, as heat favours the formation of reactant.

16. The value of equilibrium constant depends upon





... Answer is d)
Explanation: Kc is the ratio of concentration of products to concentration of reactants. In endothermic reactions, heat is involved in reactant side (i.e., Reactant + heat .......> Product) and in exothermic reaction, heat is involved in product side (i.e., Reactant .......> Product + heat) . If we increase the temperature, endothermic reaction will move in forward direction with increase in concentration of products and exothermic reaction will move in reverse direction with increase in concentration of reactants to re-establish the equilibrium. As a result, concentration of reactant and product will be changed. Hence, Kc will become larger in endothermic reaction and smaller in exothermic reaction. All reversible chemical reactions are either endothermic or exothermic, so, Kc is temperature dependent..
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