Question

For a certain reaction at constant pressure, ∆H = -15kJ, and 22 kJ of expansion work is done on the system. What is ∆U for this process?

So I know
∆= ∆U + Work flow

If work is being done on the system, shouldn't work flow be positive? So I assumed it was:

-15kJ = ∆U + 22 kJ
-37kJ = ∆U

but the answer is 7kJ.

What am I doing that's wrong? Thanks.

Answer 1

Expansion is lost, so 22kJ should be -22kj. Plugging in your values, you will get 7kj.

-15kJ=∆U + (-22kJ)
-15kj+22kj=∆U
7kj=∆U