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Ch.16 - Chemical Equilibrium
Chapter 16, Problem 34a

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

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Identify the relationship between Kc and Kp using the equation: Kp = Kc(RT)^Δn.
Determine Δn, the change in moles of gas, by subtracting the sum of the moles of gaseous reactants from the sum of the moles of gaseous products. For the reaction I2(g) + Cl2(g) ⇌ 2 ICl(g), calculate Δn.
Use the ideal gas constant R = 0.0821 L·atm/(mol·K) and the temperature T = 298 K.
Substitute the values of Kc, R, T, and Δn into the equation Kp = Kc(RT)^Δn.
Simplify the expression to find the value of Kp.

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Key Concepts

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

Equilibrium Constant (Kc and Kp)

The equilibrium constant (K) quantifies the ratio of the concentrations of products to reactants at equilibrium for a given reaction. Kc refers to concentrations in molarity, while Kp refers to partial pressures in atmospheres. The relationship between Kc and Kp is given by the equation Kp = Kc(RT)^(Δn), where Δn is the change in moles of gas, R is the ideal gas constant, and T is the temperature in Kelvin.
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Partial Pressure

Partial pressure is the pressure exerted by a single component of a gas mixture. According to Dalton's Law, the total pressure of a gas mixture is the sum of the partial pressures of its individual gases. In the context of Kp, the partial pressures of the gaseous reactants and products are used to calculate the equilibrium constant, reflecting the behavior of gases in a reaction.
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Temperature Dependence of K

The value of the equilibrium constant (K) is temperature-dependent, meaning it can change with variations in temperature. For exothermic reactions, increasing temperature typically decreases K, while for endothermic reactions, it increases K. Understanding this dependence is crucial when calculating Kp from Kc, as the temperature at which the equilibrium constants are measured must be consistent.
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