Write an equilibrium expression for each chemical equation involving one or more solid or liquid reactants or products: a. CO32-(aq) + H2O(l) ⇌ HCO3-(aq) + OH-(aq) b. 2 KClO3(s) ⇌ 2 KCl(s) + 3 O2(g) c. HF(aq) + H2O(l) ⇌ H3O+(aq) + F-(aq) d. NH3(aq) + H2O(l) ⇌ NH4+(aq) + OH-(aq)

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Identify the states of matter for each species in the chemical equation. Remember that solids (s) and liquids (l) are not included in the equilibrium expression.

For each reaction, write the equilibrium expression as the ratio of the concentrations of the products to the reactants, excluding solids and liquids.

For reaction (a), the equilibrium expression is: \( K_{eq} = \frac{[\text{HCO}_3^-][\text{OH}^-]}{[\text{CO}_3^{2-}]} \).

For reaction (b), since both reactants and some products are solids, the equilibrium expression only includes the gaseous product: \( K_{eq} = [\text{O}_2]^3 \).

For reactions (c) and (d), write the equilibrium expressions as: \( K_{eq} = \frac{[\text{H}_3\text{O}^+][\text{F}^-]}{[\text{HF}]} \) and \( K_{eq} = \frac{[\text{NH}_4^+][\text{OH}^-]}{[\text{NH}_3]} \) respectively.

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Equilibrium Expression

An equilibrium expression is a mathematical representation of the relationship between the concentrations of reactants and products at equilibrium for a reversible chemical reaction. It is formulated using the law of mass action, where the concentration of products is raised to the power of their coefficients and divided by the concentration of reactants raised to their coefficients. Solids and liquids are excluded from the expression since their activities are considered constant.

Activity of Solids and Liquids

In the context of equilibrium expressions, the activity of solids and liquids is defined as 1, meaning they do not appear in the equilibrium constant expression. This is because their concentrations do not change during the reaction, as they are in a pure state. Therefore, only aqueous and gaseous species are included in the equilibrium expression, reflecting their variable concentrations.

Aqueous and Gaseous Species

Aqueous (aq) species are substances dissolved in water, while gaseous (g) species are in the form of gas. In equilibrium expressions, the concentrations of these species are crucial as they directly influence the position of equilibrium. The presence of these species in the reaction allows for the calculation of the equilibrium constant, which indicates the extent of the reaction and the relative amounts of products and reactants at equilibrium.

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Related Practice

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Calculate Kc for each reaction. b. N2(g) + O2(g) ⇌ 2 NO(g) Kp = 4.10×10^–31 (at 298 K)

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Calculate Kp for each reaction. a. I2(g) + Cl2(g) ⇌ 2 ICl(g) Kc = 81.9 (at 298 K)

Textbook Question

Calculate Kp for each reaction. b. CH4(g) + H2O(g) ⇌ CO(g) + 3 H2(g) Kc = 1.3×10^22 (at 298 K)

Textbook Question

Consider the reaction: N₂(g) + 3 H₂(g) ⇌ 2 NH₃(g) Complete the table. Assume that all concentrations are equilibrium concentrations in M.

T (K) [N₂] [H₂] [NH₃] K_c

500 0.115 0.105 0.439 _

575 0.110 _ 0.128 9.6

775 0.120 0.140 _ 0.0584

Textbook Question

Consider the following reaction: H₂(g) + I₂(g) ⇌ 2 HI(g) Complete the table. Assume that all concentrations are equilibrium concentrations in M.

T (°C) [H₂] [I₂] [HI] Kc

25 0.0355 0.0388 0.922 _

340 _ 0.0455 0.387 9.6

445 0.0485 0.0468 _ 50.2