# CHEMISTRY- vapour pressure

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Bromobenzene, C6H5Br, and chlorobenzene, C6H5Cl, form essentially ideal solutions in all proportions. At 100°C, the equilibrium vapour pressure of bromobenzene is 137mmHg and that of chlorobenzene is 285mmHg. Calculate the equilibrium vapour pressure above a 17.6% (w/w) solution of bromobenzene in chlorobenzene at a temperature of 100°C
16305 mmHg
163 mmHg
25895 mmHg
265 mmHg
157 mmHg

• CHEMISTRY- vapour pressure -

Are you sure the 25895 choice is not 258.95?

• CHEMISTRY- vapour pressure -

Since the solution is 17.6% in bromobenene, that means 17.6 g/100 g soln OR
17.6 g bromobenzene in a solution made up of 17.6 g bromogenzene and (100-17.6 = 82.4 g chlorobenzene).
Determine moles bromo and moles chloro.
Calculate mole fraction bromo and chloro.
Then vapor pressure of each component is
P = X*Po
You will have one partial pressure for the bromo and one partial pressure for th chlor. Add them for the total pressure. Post your work if you get stuck.

• CHEMISTRY- vapour pressure -

i have 0.112 mol of bromo,
and 0.732 mol chloro,
but i am stuck on the mole fraction.
Do i just do 1-0.112= 0.888 or am i missing a step?

• CHEMISTRY- vapour pressure -

ok, this is what I have.
Xbromo= 0.112/+0.732+0.112=0.133
Xchloro= 1-0.133= 0.867
P=Xbromo*p= 0.133*137= 18.221mmHg
P=Xchloro*p= 0.867*285= 247.095mmHg
so I add 18.221+247.095= 265.316mmHg
Is that right?

• CHEMISTRY- vapour pressure -

correct

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