TextBook Problem 4B 7.

[Nailea_Espinal_1K]

In a combustion chamber, the total internal energy change produced from the burning of a fuel is 22573 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?

For this question, I am having a hard time understanding how the 947 kj of heat is negative. I would assume it would be positive because it is saying that the cooling system absorbs 947 kj of heat. Would I be using the formula delta U= q +w, rewritten as w=delta U -q?

Thank you

[Anita Sarransingh 2A]

Hi! The amount of heat entering the cooling system would be positive, but this heat was taken away from the fuel in the chamber. Since the question is asking how much work can be done by the fuel, the 947 kJ of heat would be negative since this heat is lost by the fuel and gained by the cooling system. The equation w = delta U - q looks correct.

[Emma MacLachlan 1D]

I agree. The system in this case is the chamber in which the combustion is occurring. Therefore, if the total internal energy of the system is 2573 kJ and 947 kJ is being absorbed by the cooling system (which is part of the surroundings), then this value of q would be negative relative to the system.