To find out which substance cancels out when combining the two given intermediate chemical equations, we should follow the steps below:
1. Identify the given equations:
[tex]\[
2 P (s) + 3 Cl_2 (g) \rightarrow 2 PCl_3 (l)
\][/tex]
[tex]\[
PCl_3 (l) + Cl_2 (g) \rightarrow PCl_5 (s)
\][/tex]
2. Observe which substances appear in both equations:
- The first equation produces \(2 PCl_3 (l)\).
- The second equation consumes \(PCl_3 (l)\).
3. Combine the two equations:
To combine them, we add the reactions and cancel out any substance that appears on both the reactant and product sides:
[tex]\[
2 P (s) + 3 Cl_2 (g) \rightarrow 2 PCl_3 (l)
\][/tex]
[tex]\[
PCl_3 (l) + Cl_2 (g) \rightarrow PCl_5 (s)
\][/tex]
4. Cancel out the common substance:
Since \(PCl_3 (l)\) appears as a product in the first equation and as a reactant in the second equation, it will cancel out when we combine the equations:
[tex]\[
(2 P (s) + 3 Cl_2 (g) \rightarrow 2 PCl_3 (l)) + (PCl_3 (l) + Cl_2 (g) \rightarrow PCl_5 (s))
\][/tex]
Simplifies to:
[tex]\[
2 P (s) + 3 Cl_2 (g) + PCl_3 (l) + Cl_2 (g) \rightarrow 2 PCl_3 (l) + PCl_5 (s)
\][/tex]
After canceling the \(2 PCl_3 (l)\) that appears on both sides:
[tex]\[
2 P (s) + 4 Cl_2 (g) \rightarrow PCl_5 (s)
\][/tex]
Thus, the substance that cancels out when combining the equations is \(PCl_3\).
Therefore, the correct answer is [tex]\(PCl_3\)[/tex].
