1.) Calculate the change in internal energy of the following system: a balloon i

Question

1.) Calculate the change in internal energy of the following system: a balloon is cooled by removing 0.655kJ of heat. It shrinks on cooling, and the atmosphere does 387J of work on the balloon.

2.) Calculate the change in internal energy of the following system: a 100.0-g bar of gold is heated from 25 ?C to 50 ?C during which it absorbs 322 J of heat. Assume the volume of the gold bar remains constant.

3.) Calculate the change in internal energy of the following system: the surroundings do 1.41kJ of work compressing gas in a perfectly insulated cylinder.

Explanation / Answer

?U = change in internal energy
?U = W + Q
W = work done
Q = heat transfer

1.
?U = -655J + 388J = -267J
Note: 655J is negative because the heat was removed from the balloon. 388J is postive because work in done on the balloon. Since ?U is negative, the process is exothermic because the process releases more energy than accepts.

2.

The question about the bar of gold requires no math. It says that it absorbs 322 J of heat, therefore the internal energy changed by 322 J

For the third, realize that the change in internal energy of a substance in an insulated container has the same value as the change in pressure. Therefore, the answer is 1.44 kJ of work

These problems look more difficult at first glance than they really are. Don't over-complicate them.

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