Page **1** of **1**

### HW problem 8.5

Posted: **Thu Jan 31, 2019 12:35 pm**

by **Samantha Jimenez 4k**

A gas sample in a cylinder is supplied with 524 kJ of energy as heat. At the same time, a piston compresses the gas, doing 340 kJ of work. What is the change in internal energy of the gas during this process?

For this problem is the 524kJ the initial energy and the 340kJ just the change? so would the change just be 340 kJ??? I'm confused on this question.

### Re: HW problem 8.5

Posted: **Thu Jan 31, 2019 1:05 pm**

by **Iris Bai 2K**

Both changes in energy are acting on the gas, so the change in energy of the gas is just the addition of the two values.

### Re: HW problem 8.5

Posted: **Thu Jan 31, 2019 5:43 pm**

by **Neil Hsu 2A**

To expand, change in internal energy is the work done on the system plus the change in enthalpy (or heat at constant pressure). In other words, delta(U) = delta(H) + W. In the problem, the 524 kJ of heat is your delta(H) and the 340 kJ of work done by the piston is your W. Therefore, your change in internal energy delta(U) is the sum of the two values.

### Re: HW problem 8.5

Posted: **Thu Jan 31, 2019 6:01 pm**

by **tierra parker 1J**

the system is the gas and everything else around it is the surroundings. heat is being added to the system so 524 kj is positive then work is being done to the system so 340 kj is also positive then the total change in internal energy is the two numbers added together.