Write a balanced chemical equation for the reaction in which phosphorus burns in chlorine to form phosphorus pentachloride.

(N/A) The chemical reaction involves phosphorus $(P_4)$ reacting with chlorine gas $(Cl_2)$ to produce phosphorus pentachloride $(PCl_5)$.
The unbalanced equation is: $P_4 + Cl_2 \longrightarrow PCl_5$.
To balance the phosphorus atoms,we place a coefficient of $4$ before $PCl_5$: $P_4 + Cl_2 \longrightarrow 4PCl_5$.
To balance the chlorine atoms,we need $20$ chlorine atoms on the reactant side,so we place a coefficient of $10$ before $Cl_2$: $P_4(s) + 10Cl_2(g) \longrightarrow 4PCl_5(g)$.