Question

Phosphorus pentachloride decomposes to phosphorus trichloride and chlorine gas at elevated temperatures by the following reaction: PCl5(g) PCl3(g) + Cl2(g). If Kc = 1.8 at 250°C, what is the value of Kp at the same temperature? Can someone show me how to get the answer?

Answer 1

To find the value of Kp for the decomposition of phosphorus pentachloride into phosphorus trichloride and chlorine gas, use the relationship Kp = Kc(RT)^Δn. With Kc = 1.8, R = 0.0821 atm·L/mol·K, T = 523.15 K, and Δn = 1, calculate Kp by substituting these values into the formula.

Step-by-step explanation:

The equilibrium constant for the decomposition of phosphorus pentachloride (PCl5) into phosphorus trichloride (PCl3) and chlorine gas (Cl2) can be expressed in terms of either Kc (concentration-based) or Kp (pressure-based). The relationship between Kc and Kp can be derived from the ideal gas law and is given by the equation Kp = Kc(RT)Δn, where R is the gas constant, T is the temperature in Kelvin, and Δn is the change in moles of gas from reactants to products.

In the given reaction, Δn is equal to (1 + 1) - 1 = 1. At 250°C, which is 523.15 K, Kc is given as 1.8. The gas constant R is 0.0821 atm·L/mol·K. To calculate Kp, plug in these values: Kp = 1.8 (0.0821 atm·L/mol·K × 523.15 K)1 = 1.8 × 0.0821 × 523.15.