My questions are If the system does work what is the sign of w and why? Also in an exothermic and endothermic reaction what is the sign of w and why?

Question

My questions are If the system does work what is the sign of w and why? Also in an exothermic and endothermic reaction what is the sign of w and why?

Answer 1

Hi Eric,

If the system does work the sign is negative since the system is "using" or converting energy to do the work.

It is similar to when you do work, you decrease the amount of your energy available to do more work. Without adding more food (source of energy) to your system you run out of energy to do more work!

For exothermic and endothermic reactions, w is not involved directly so only q changes. Exothermic is negative q since heat is lost to the surroundings. Endothermic is positive q since heat will be gained from the surroundings.