Question

The gas in a piston (defined as the system) is warmed and absorbs 655 J of heat. The expansion performs 346 J of work on the surroundings. Part A What is the change in internal energy for the system?

Answer 1

Ans. Change in internal energy, dU = q + w                   - equation 1

            Where,

                        q = heat gained.

By convention, heat gained by system is denoted by “+ q” or positive value of q.

            So, q = 655 J = + 655 J

                        w = work done by system.

By convention, work done by system is a “- w” or negative value of w.

            So, w = - 346 J

Putting the values in equation 1-

            dU = 655 J + (- 346 J) = 655 J – 346 J = + 309 J = 309 J

Hence, change in internal energy = 309 J

Note: The + sign of dU indicates that the system gained 309 J of energy during the change.