# Chemical equilibrium problems and solutions

1. What is chemical equilibrium? Solution: Chemical equilibrium is a state in a chemical reaction where the concentrations of both reactants and products remain constant over time, due to the forward reaction rate equalling the reverse reaction rate.

2. What does the equilibrium constant (K) signify in a chemical equilibrium? Solution: The equilibrium constant (K) is a measure of the concentrations of the products and reactants at equilibrium. It is a specific value for a given reaction at a specific temperature.
3. How is the equilibrium constant (K) calculated for the reaction: aA + bB ⇌ cC + dD? Solution: The equilibrium constant K is calculated using the expression K = ([C]c x [D]d) / ([A]a x [B]b) where [A], [B], [C], and [D] are the equilibrium concentrations of the reactants and products, and a, b, c, and d are their stoichiometric coefficients.
4. What is Le Chatelier’s principle? Solution: Le Chatelier’s principle states that if a change in conditions is applied to a system at equilibrium, the system will adjust to counteract the change and restore equilibrium.
5. How does a change in temperature affect the position of equilibrium? Solution: If a reaction is exothermic (releases heat), increasing the temperature will shift the equilibrium towards the reactants. Conversely, for an endothermic reaction (absorbs heat), increasing the temperature will shift the equilibrium towards the products.
6. How does a change in pressure affect the position of equilibrium in a gaseous reaction? Solution: Increasing the pressure will shift the equilibrium towards the side of the reaction with fewer moles of gas, thus reducing the pressure. Conversely, decreasing the pressure shifts the equilibrium towards the side with more moles of gas.
7. What is the difference between Kc and Kp? Solution: Kc is the equilibrium constant in terms of molar concentrations, while Kp is the equilibrium constant in terms of partial pressures. They are used for reactions in solution and in the gaseous phase, respectively.
8. What does it mean when K > 1 and when K < 1? Solution: When K > 1, it means the products are favored at equilibrium (the reaction tends to proceed towards the products). When K < 1, it means the reactants are favored at equilibrium (the reaction tends to proceed towards the reactants).
9. How does the addition of a catalyst affect chemical equilibrium? Solution: The addition of a catalyst does not affect the position of the chemical equilibrium. It only speeds up the rate at which equilibrium is reached by lowering the activation energy for both the forward and reverse reactions.
10. How does a change in concentration affect the position of equilibrium? Solution: According to Le Chatelier’s principle, if the concentration of a reactant or product is changed, the system will shift to counteract this change. If a reactant is added, the system will shift towards the products to consume the added reactant, and vice versa.
11. What are homogeneous and heterogeneous equilibria? Solution: Homogeneous equilibria involve reactants and products in the same phase, while heterogeneous equilibria involve reactants and products in different phases.
12. How does the equilibrium constant change with temperature? Solution: The equilibrium constant is temperature-dependent. If the forward reaction is exothermic, K decreases with increasing temperature. If the forward reaction is endothermic, K increases with increasing temperature.
13. What is the reaction quotient (Q), and how does it relate to the equilibrium constant (K)? Solution: The reaction quotient (Q) is calculated in the same way as the equilibrium constant, but it uses the concentrations or pressures that are present at any given time instead of at equilibrium. If Q > K, the reaction will proceed to the left (towards reactants), and if Q < K, it will proceed to the right (towards products).
14. What are conjugate acids and conjugate bases? Solution: A conjugate acid is the species formed by the addition of a proton (H⁺) to a base, and a conjugate base is the species formed by the removal of a proton from an acid.
15. What is an acid dissociation constant (Ka)? Solution: Ka is the equilibrium constant for the dissociation of an acid into a proton and its conjugate base. It provides a quantitative measure of the strength of an acid in solution.
16. What is a base dissociation constant (Kb)? Solution: Kb is the equilibrium constant for the dissociation of a base into a hydroxide ion and its conjugate acid. It provides a quantitative measure of the strength of a base in solution.
17. What does it mean for a reaction to be at “dynamic equilibrium”? Solution: A dynamic equilibrium means that the forward and reverse reactions are still happening, but they are occurring at the same rate, resulting in no net change in the concentrations of the reactants or products.
18. What is meant by “shift to the right” or “shift to the left” in the context of chemical equilibrium? Solution: A “shift to the right” in a chemical equilibrium means that the system is making more products to reach equilibrium, while a “shift to the left” means that the system is making more reactants.
19. What are the units of the equilibrium constant K? Solution: The units of K depend on the reaction and are related to the molar concentrations of the substances involved in the reaction. However, for some reactions, particularly those involving gases, the units may be omitted.
20. What is the difference between a reversible and an irreversible reaction? Solution: A reversible reaction is one where the reactants form products, which then react together to give the reactants back, and can reach a chemical equilibrium. An irreversible reaction proceeds only in one direction from reactants to products, and does not reach a chemical equilibrium.

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