Question

$a$ moles of $PC{l}_5$, undergoes. thermal dissociation as : $PC{l}_5\rightleftharpoons PC{l}_3+C{l}_2$, the mole fraction of $PC{l}_3$ at equilibrium is 0.25 and the total pressure is 2.0 atmosphere. The partial pressure of $C{l}_2$ at equilibrium is:

• A. $2.5$
• B. $1.0$
• C. $0.5$
• D. none of these

Answer 1

Answer: (C)

$0.5$

$PC{l}_5\rightleftharpoons PC{l}_3+C{l}_2$

Initial	$a$	0	0
Final	$a-ax$	$ax$	$ax$

At equilibrium, moles of $C{l}_2=$ moles of $PC{l}_3$
Given mole fraction of $PC{l}_3$ at equilibrium is $0.25$
Therefore mole fraction of $C{l}_2=0.25$
Partial pressure of $C{l}_2=$ mole fraction $\times$ total pressure $=0.25\times 2=0.5$