Equilibria - exam practice

Which statement about the effect of a catalyst on a reversible reaction is correct?

Chloroethene, CH₂=CHCl, is prepared in the presence of a solid catalyst using the equilibrium reaction below.

CH₂ClCH₂Cl_(g) ⇌ CH₂=CHCl_(g) + HCl_(g) ΔH = +51 kJ mol^-1

Which change would result in an increased equilibrium yield of chloroethene?

Hydrogen gas can be produced as shown below.

CH_4(g) + H₂O_(g) ⇌ CO_(g) + 3H_2(g) ΔH = +206 kJ mol^-1

Which conditions produce the greatest equilibrium yield of hydrogen?

A pale brown mixture of NO₂ and N₂O₄ is allowed to reach equilibrium in a sealed gas syringe according to the following equation.

2NO_2(g) ⇌ N₂O_4(g)

When the plunger is pushed further into the syringe the pressure increases and the mixture becomes paler in colour.

When the syringe is placed in a hot oven the mixture becomes darker in colour.

Which of the following statements is correct?

Which statement is not always correct for a reaction at equilibrium?

reactants ⇌ products