The decomposition of phosgene. ${\text{COCl}}_{\text{2}\left(\text{g}\right)}\rightleftharpoons {\text{\hspace{0.17em}CO}}_{\left(\text{g}\right)}{\text{\hspace{0.17em}+\hspace{0.17em}Cl}}_{\text{2}\left(\text{g}\right)}$, is an endothermic process. Which of  the following factors will cause the value of the equilibrium constant to increases?