In a cylinder of gas if energy is added to the system either the internal
energy (U)( temperature ) increases or the volume expands or both.
Assume no change in volume. Then delta T will be positive as will added
energy (Q) ....right
Now assume T is unchanged, then P( delta V) must equal the Q and delta V
is positive as well as the volume expands doing work ON the surroundings.
Thus, I have the equation as : Q = delta U + W
I like W>0 for work done by the system.
I am also all ears.
Ken Fox
AP/IB Physics Teacher
Smoky Hill High School
Aurora, CO