Equilibrium Constant Kp and Gaseous Equilibria

This set of vocabulary flashcards covers concepts related to gaseous equilibria, including partial pressures, mole fractions, the equilibrium constant Kp, and the application of Le Chatelier's principle to industrial processes like the Haber and Contact processes.

Pascal (Pa)

The SI unit of pressure; $1\,\text{pascal}$ is a pressure of $1\,\text{newton per square metre}\,(\text{Nm}^{-2})$.

Partial pressure (p)

The pressure that an individual gas in a mixture would exert if it occupied the container on its own.

Total pressure

The sum of the partial pressures of all the gases in a mixture.

Mole fraction of a gas A

$$\frac{\text{number of moles of gas A in the mixture}}{\text{total number of moles of gas in the mixture}}$$

Mathematical expression for partial pressure p of A

$$\text{partial pressure p of A} = \text{mole fraction of A} \times \text{total pressure}$$

Equilibrium constant Kp

The equilibrium constant for reversible reactions in the gas phase expressed in terms of partial pressures.

Haber process equation

$$3H_2(g) + N_2(g) \rightleftharpoons 2NH_3(g)$$

Kp unit for the Haber process synthesis

$$Pa^{-2}$$

Standard enthalpy change (\Delta H) of the Haber process

$$-92\,kJ\,mol^{-1}$$

Effect of temperature on Kp for exothermic reactions

Increasing the temperature decreases $K_p$ as the equilibrium is forced to the left to absorb heat.

Le Chatelier's principle for pressure in gaseous equilibria

Increasing the pressure forces the equilibrium toward the side with fewer molecules to reduce the total pressure.

Effect of pressure on the equilibrium 2HI(g) ⇌ H2(g) + I2(g)

Pressure has no effect on the equilibrium position because there is no change in the total number of molecules on either side of the reaction.

Effect of increasing pressure on reaction rate

Increases the rate at which equilibrium is reached because there will be more collisions between molecules.

Contact process key stage reaction

$2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g)$, with $\Delta H = -197\,kJ\,mol^{-1}$ or $-192\,kJ\,mol^{-1}$ as cited in various notes contexts.