To determine the equilibrium constant, Kc, for a given chemical reaction, we need to focus on the concentrations of the products and reactants at equilibrium. The expression for Kc is derived from the balanced chemical equation and involves the concentrations of gaseous and aqueous species, while solids and liquids are not included in the expression. Let’s break down each of the reactions you provided.
1. Reaction: 2NOCl (g) ⇌ 2NO (g) + Cl2 (g)
For this reaction, the equilibrium constant expression is based on the concentrations of the gaseous products and reactants. The balanced equation shows that 2 moles of NOCl produce 2 moles of NO and 1 mole of Cl2. The Kc expression is:
- Kc = [NO]^2 [Cl2] / [NOCl]^2
2. Reaction: 2Cu(NO3)2 (s) ⇌ 2CuO (s) + 4NO2 (g) + O2 (g)
In this case, the reactants Cu(NO3)2 and CuO are solids, and thus their concentrations do not appear in the Kc expression. We only consider the gaseous products, NO2 and O2. The Kc expression is:
3. Reaction: CH3COOC2H5(aq) + H2O(l) ⇌ CH3COOH(aq) + C2H5OH(aq)
Here, we have aqueous reactants and products. Water is a liquid, so it is not included in the Kc expression. The Kc expression for this reaction is:
- Kc = [CH3COOH][C2H5OH] / [CH3COOC2H5]
4. Reaction: Fe3+ (aq) + 3OH– (aq) ⇌ Fe(OH)3 (s)
In this reaction, Fe(OH)3 is a solid, so it does not appear in the Kc expression. We only include the aqueous species in the expression. Thus, the Kc expression is:
5. Reaction: I2 (s) + 5F2 ⇌ 2IF5
For this reaction, I2 is a solid, and we only consider the gaseous reactant F2 and the product IF5. The Kc expression is:
In summary, when writing the equilibrium constant expressions, remember to only include the concentrations of gases and aqueous solutions, while excluding solids and liquids. This approach helps in understanding how the equilibrium position is influenced by the concentrations of the reactants and products involved in the reaction.
