Write the equilibrium expression for each of the following reactions: (a) $2 \mathrm{~N}_2 \mathrm{O}(g) \rightleftarrows 2 \mathrm{~N}_2(g)+\mathrm{O}_2(g)$ (d) $\mathrm{CO}(g)+\mathrm{H}_2 \mathrm{O}(g) \rightleftarrows \mathrm{CO}_2(g)+\mathrm{H}_2(g)$ (b) $2 \mathrm{NOBr}(g) \rightleftarrows 2 \mathrm{NO}(g)+\mathrm{Br}_2(g)$ (e) $\mathrm{CH}_4(g)+2 \mathrm{H}_2 \mathrm{~S}(g) \rightleftarrows \mathrm{CS}_2(g)+4 \mathrm{H}_2(g)$ (c) $\mathrm{HF}(a q) \rightleftarrows \mathrm{H}^{+}(a q)+\mathrm{F}^{-}(a q)$ (f) $\mathrm{H}_2 \mathrm{C}_2 \mathrm{O}_4(a q) \rightleftarrows 2 \mathrm{H}^{+}(a q)+\mathrm{C}_2 \mathrm{O}_4^{2-}(a q)$

For each change indicated, determine whether the equilibrium

$$\mathrm{PCl}_3(g)+\mathrm{Cl}_2(g) \rightleftarrows \mathrm{PCl}_5(g)$$

will shift to the right, shift to the left, or neither: (a) addition of $\mathrm{PCl}_3(\mathrm{~g})$, (b) removal of $\mathrm{PCl}_3(\mathrm{~g})$, (c) removal of $\mathrm{PCl}_5(\mathrm{~g})$, and (d) removal of $\mathrm{Cl}_2(g)$.

Which of the following statements is correct about a system at equilibrium? (a) The concentrations of reactants are equal to the concentrations of products. (b) The concentrations of reactants must be present in exact stoichiometric amounts. (c) The rate of product formation is equal to the rate of reactant formation.

Give an example of dynamic equilibrium in your everyday life.

What is meant by the term dynamic equilibrium?