Quick questions on Chemical equilibria, Kc and Kp: Singapore A-Level H2 Chemistry

A reversible reaction reaches dynamic equilibrium when the forward and backward reactions proceed at equal rates in a closed system, so the concentrations of all species stay constant (though the reactions continue). Both reactions are still occurring; nothing has stopped.

A large $K$ ($\gg 1$) means products are favoured at equilibrium; a small $K$ ($\ll 1$) means reactants are favoured. The value of $K$ depends only on temperature. Changing concentration or pressure shifts the position of equilibrium but does not change $K$.

Write the $K_p$ expression for $\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g)$ and state its units. [2 marks]

State the effect on the value of $K_c$ of (a) adding a catalyst and (b) raising the temperature of an endothermic reaction. [2 marks]

$2.0$ mol of A and $2.0$ mol of B in a $1$ dm cubed flask reach equilibrium $\text{A} + \text{B} \rightleftharpoons \text{C}$ with $1.5$ mol of C formed. Calculate $K_c$. [3 marks]