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Question

If 3.0 J  of work is done on a system and the internal energy of the system increases by 17.0 J,  how much heat was added to the system?

Answer 1

This is a type of internal energy problem that makes use of the equation ΔU = Q + W where U is the internal energy, Q is the heat and W is the heat.

Because the positive or negative values play an important part in the equation, it is crucial that you memorize the following graph that is commonly found in textbooks.:

work done by system on surroundings -w

work done on system by surroundngs +w

heard absorbed by system +Q

head absorbed by the surroundings -Q

Given this, we know that the 3.0 J of work is being done on the system, so it will + 3.0 J; the internal energy increases so this will be +17 J, and the heat being added to the system will have a + value. The equation will look like this:

ΔU = ΔQ + Δw

17 J = Q + 3.0 J (Solve for Q)

14 J = Q

14 J of heat was added to the system.