Quick questions on Chemical equilibrium and Le Chatelier's principle: WACE Year 12 Chemistry

Le Chatelier's principle predicts which way a system at equilibrium shifts when it is disturbed: the system responds in the direction that partially counteracts the imposed change. Use it to predict the qualitative effect of three changes.

Adding a reactant shifts the position of equilibrium towards the products (the system consumes some of the added reactant). Removing a product also shifts towards products. Adding a product, or removing a reactant, shifts back towards reactants.

Increasing the pressure by decreasing the volume shifts equilibrium towards the side with fewer moles of gas, because that reduces the total pressure. Decreasing pressure shifts towards the side with more moles of gas. If both sides have equal moles of gas, a pressure change has no effect on position.

This is the only change that alters the value of $K_c$. Treat heat as a reactant or product using the sign of $\Delta H$. For an exothermic forward reaction ($\Delta H$ negative), heat is a product, so increasing temperature shifts equilibrium towards reactants and decreases $K_c$.

A catalyst speeds up the forward and reverse reactions equally. It makes equilibrium reached faster but does not shift the position and does not change $K_c$ or yield.