In the internal-combustion engine in an automobile, hot compressed gas expands against a piston, turning the driveshaft that moves the vehicle along the road. If you are investigating the performance of such an engine, you might need to assess the work that each stroke of the piston can achieve. Suppose a gas expands by 500. mL (0.500 L) against the opposing force due to the transmission, which is modeled as a pressure of 1.20 atm and no heat is exchanged with the surroundings during the expansion.

(a) How much work is done in the expansion?

(b) What is the change in internal energy of the system?

ANTICIPATE Because work is done by the system, expect w and therefore ΔU to be negative, signifying that energy has been lost from the system.

PLAN Use Eq. 3 to calculate the work, and then convert liter-atmospheres into joules.

What should you assume? Assume that the only energy exchanged with the surroundings is the work of expansion.

Transcribed Image Text:

w = -Pex AV (3)