4B.7

$\Delta U=q+w$

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JamieVu_2C
Posts: 108
Joined: Thu Jul 25, 2019 12:16 am

4B.7

In a combustion chamber, the total internal energy change produced from the burning of a fuel is -2573 kJ. The cooling system that surrounds the chamber absorbs 947 kJ as heat. How much work can be done by the fuel in the chamber?

In the solutions manual, it says that q = –947 kJ. How is q negative if the system absorbs 947 kJ; shouldn't q = +947 kJ instead?

Jonathan Gong 2H
Posts: 105
Joined: Sat Jul 20, 2019 12:16 am

Re: 4B.7

q is negative because it is not the combustion chamber that absorbs the heat, it is the cooling system that surrounds it. Thus, the combustion chamber is losing heat, which means that q should be -947 kJ when its internal energy or work is being calculated.

Andrew Pfeiffer 2E
Posts: 101
Joined: Sat Sep 28, 2019 12:16 am

Re: 4B.7

Q is negative because it's about the work that is done by the fuel, not the work done on the cooling chamber. The fuel is combusted and releases energy; therefore it is exothermic.

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