Question

Nitrogen and oxygen react at high temperatures.

(a) Write the expression for the equilibrium constant \(\left( {{K_c}} \right)\)for the reversible reaction

\(\Delta H = 181kJ\)

(b) What will happen to the concentrations of \({N_2},{O_2}, and\;NO\)at equilibrium if more \({O_2}\)is added?

(c) What will happen to the concentrations of \({N_2},{O_2}, and\;NO\)at equilibrium if \({N_2}\)is removed?

(d) What will happen to the concentrations of \({N_2},{O_2}, and\;NO\) at equilibrium if \(NO\)is added?

(e) What will happen to the concentrations of \({N_2},{O_2}, and\;NO\)at equilibrium if the pressure on the system is increased by reducing the volume of the reaction vessel?

(f) What will happen to the concentrations of \({N_2},{O_2}, and\;NO\) at equilibrium if the temperature of the system is increased?

(g) What will happen to the concentrations of \({N_2},{O_2}, and\;NO\) at equilibrium if a catalyst is added?

Short answer

The concentration of the expression added or removed at equilibrium is

(a)\({K_c} = \frac{{N{O^2}}}{{\left[ {{N_2}} \right] \cdot \left[ {{O_2}} \right]}}\)

(b)\(\left[ {{{\rm{O}}_2}} \right],[{\rm{NO}}]\)will increase,\(\left[ {{{\rm{N}}_2}} \right]\)will decrease

(c)\(\left[ {{{\rm{N}}_2}} \right],[{\rm{NO}}]\)will decrease, \(\left[ {{{\rm{O}}_2}} \right]\)will increase

(d)\([{\rm{NO}}],\left[ {{{\rm{N}}_2}} \right],\left[ {{{\rm{O}}_2}} \right]\)will increase

(e)\([{\rm{NO}}],\left[ {{{\rm{N}}_2}} \right],\left[ {{{\rm{O}}_2}} \right]\)will remain the same

(f)\([{\rm{NO}}]\)Will increase,\(\left[ {{{\rm{N}}_2}} \right],\left[ {{{\rm{O}}_2}} \right]\)will decrease

(g)\([{\rm{NO}}],\left[ {{{\rm{N}}_2}} \right],\left[ {{{\rm{O}}_2}} \right]\) will remain the same.

Step-by-step solution

Addition or removal of concentrations of given equation at equilibrium for  parts (a), (b), and (c)

The reaction,

\({\rm{\Delta H}} = 181{\rm{kJ}}\)

(a) Let us write the expression for the equilibrium constant for the given reversible reaction

\({K_c} = \frac{{{{[NO]}^2}}}{{\left[ {{N_2}} \right] \cdot \left[ {{O_2}} \right]}}\)

(b)Let us see what will happen if more\({{\rm{O}}_2}\)is added.

If\({{\rm{O}}_2}\)is added, excess\({{\rm{O}}_2}\)will react with\({{\rm{N}}_2}\)and produce more of\({\rm{NO}}\). Therefore, the concentration of\({{\rm{O}}_2}\)and\({\rm{NO}}\)will increase, and the concentration of\({{\rm{N}}_2}\)will decrease.

(c)Let us see what will happen if\({{\rm{N}}_2}\)is removed.

If\({{\rm{N}}_2}\)is removed, some\({\rm{NO}}\)will decompose into\({{\rm{N}}_2}\)and\({{\rm{O}}_2}\), in order to achieve a new equilibrium.

Therefore, the concentration of \({{\rm{N}}_2}\)and \({\rm{NO}}\)will decrease, and the concentration of \({{\rm{O}}_2}\) will increase.

Addition or removal of concentrations of given equation at equilibrium for  parts (d) and (e)

(d) Let us see what will happen if\({\rm{NO}}\)is added.

If\({\rm{NO}}\)is added, excess\({\rm{NO}}\)will decompose into\({{\rm{N}}_2}{\rm{and\;}}{{\rm{O}}_2}\), in order to achieve a new equilibrium. Therefore, the concentration of\({\rm{NO}},{{\rm{N}}_2},{\rm{\;and\;}}{{\rm{O}}_2}\)will increase.

(e) Let us see what will happen if the pressure on the system is increased. Since the number of moles of gas on the reactant side is equal to the number of moles of gas on the product side, change in pressure (increase) will have no effect on the equilibrium. Therefore, the concentration of \({\rm{NO}},{{\rm{N}}_2},{\rm{\;and\;}}{{\rm{O}}_2}\)will remain the same.

Addition or removal of concentrations of given equation at equilibrium for  parts (f) and (g)

(f)Let us see what will happen if the temperature of the system is increased.

Since\({\rm{\Delta H}} > 0(181{\rm{kJ}} > 0)\), the reaction is endothermic.

\({{\text{N}}_2}({\text{g}}) + {{\text{O}}_2}({\text{g}}) + {\text{heat}} \rightleftharpoons 2{\text{NO}}({\text{g}})\)

If the temperature (heat) is increased, the equilibrium will shift to the right, resulting production of NO.

Therefore, the concentration of NO will increase, and the concentration of\({{\rm{N}}_2}{\rm{\;and\;}}{{\rm{O}}_2}\)will decrease.

(g) Let us see what will happen if a catalyst is added. The addition of catalyst will increase the rate of reaction, but will have no effect on the equilibrium. Therefore, the concentration of \({\rm{NO}},{{\rm{N}}_2},{\rm{\;and\;}}{{\rm{O}}_2}\) will remain the same.