## Q 8.13

$\Delta U=q+w$

Belle Calforda3f
Posts: 67
Joined: Fri Sep 29, 2017 7:07 am

### Q 8.13

In question 8.13, why is 947 kj absorbed written as a negative q value?

Cali Rauk1D
Posts: 51
Joined: Fri Sep 29, 2017 7:03 am

### Re: Q 8.13

It is negative because heat is being absorbed from the system

404995677
Posts: 82
Joined: Fri Sep 29, 2017 7:07 am

### Re: Q 8.13

947 kJ of energy is leaving the system as heat to the surrounding

Ammarah 2H
Posts: 30
Joined: Fri Sep 29, 2017 7:06 am

### Re: Q 8.13

So just for clarification, if heat is absorbed by the system, is the value always negative?

Kelly Kiremidjian 1C
Posts: 62
Joined: Fri Sep 29, 2017 7:04 am

### Re: Q 8.13

No. In this question, it says that the cooling system that surrounds the cylinder absorbs 974 kJ of heat. If the system that surrounds the cylinder is absorbing heat, this means that the cylinder is releasing this heat and that is why it is negative.
Heat absorbed by the cylinder would be positive, heat leaving the cylinder is negative.

905022356
Posts: 48
Joined: Mon Oct 02, 2017 7:19 am

### Re: Q 8.13

I don't understand why the final answer is negative. Can someone explain it to me? thanks!

Jennie Fox 1D
Posts: 66
Joined: Sat Jul 22, 2017 3:01 am

### Re: Q 8.13

If the system is doing work on its surroundings, as in this problem, the work is negative.

Magdalena Palavecino 1A
Posts: 54
Joined: Fri Sep 29, 2017 7:04 am

### Re: Q 8.13

Does it matter if we are talking about work or heat? I understand that when heat is lost it is negative, but what about work? I am confused about these two terms

Sally Nason - 1K
Posts: 40
Joined: Fri Sep 29, 2017 7:05 am

### Re: Q 8.13

In this question, the part we are trying to figure out is the work that can be done by the system, or on the system. In general, if the system does work, such as expansion, the work value will be positive and if the system has work done on it, such as compression, the work value will be negative.

Amy Zheng 2l
Posts: 57
Joined: Fri Sep 29, 2017 7:04 am

### Re: Q 8.13

the system is doing work on the surrounding so its negative