thermochemistry

Question

A sample of flammable liquid is placed into an enclosed cylinder which is then fitted with a movable piston. Initially the cylinder contains a volume of 1.60 L. The sample is ignited producing gas and releasing 401.5 J of energy. To what volume will the cylinder expand to if it must expand against a pressure of 729.8 mmHg. Assume all the energy released is converted to work used to push the piston? 

Answer 1

work = -P∆V

work = 401.5 J

P = 729.8 mm Hg x 1 atm/760 mm = 0.960 atm

∆V = change in volume in liters = ?

Since we want the answer in liters, we should convert joules to L-atm so that the units cancel, leaving us with liters.

101.3 J = 1 L-atm

401.5 J x 1 L-atm/101.3 J = 3.96 L-atm

-3.96 L-atm = -(0.960 atm)(∆V L)

∆V = -3.96 L-atm/-0.960 atm

∆V = 4.13 L

The volume will the cylinder will expand to will be 4.13 L + 1.60 L = 5.73 L