A sample of gas occupies a volume of 638 mL As it expands it

A sample of gas occupies a volume of 63.8 mL. As it expands, it does 138.2 J of work on its surroundings at a constant pressure of 783 torr. What is the final volume of the gas?

Solution

work = - 138.2 J
= - 138.2/101.33 atm.L
= - 1.364 atm.L

P = 783 torr
= 783/760 atm
= 1.030 atm

work is negative because system is doing work on surrounding

now use:
work = -Pext*(Vf-Vi)
- 1.364 atm.L = - 1.030 atm*(Vf - 0.0638 L)
Vf - 0.0638 L = 1.3243
Vf = 1.39 L

Answer: 1.39 L