Quick questions on Equilibria - WJEC A-Level Chemistry

To use $K_p$, first find the mole fraction of each gas (its moles divided by the total moles of gas), then multiply by the total pressure to get its partial pressure. Substituting these partial pressures into the $K_p$ expression and working out the units (powers of Pa) gives the constant. This mole-fraction route is the standard method for gas-phase equilibrium calculations, and care with the total number of gas moles is where most marks are lost.

Sulfur dioxide oxidation to sulfur trioxide is run at a moderate temperature to keep $K_p$ favourable (the forward reaction is exothermic) while a vanadium(V) oxide catalyst secures a workable rate. The Haber process. A compromise temperature balances a higher $K_p$ at low temperature against an acceptable rate, the classic industrial equilibrium optimisation.

Write the $K_c$ expression for $\text{N}_2 + 3\text{H}_2 \rightleftharpoons 2\text{NH}_3$. [1 mark]

State which single factor changes the value of $K_c$. [1 mark]

State the units of $K_c$ for $\text{H}_2 + \text{I}_2 \rightleftharpoons 2\text{HI}$. [1 mark]

State the effect of increasing pressure on the value of $K_p$. [1 mark]

State how you find the partial pressure of a gas in a mixture. [1 mark]