# Thermochemistry relating delta H and q of surroundings

1. Nov 23, 2014

### garr6120

1. The problem statement, all variables and given/known data
Why does $\Delta H=\pm |q_{surroundings}|$?

2. Relevant equations

3. The attempt at a solution
Exothermic reactions have a $-\Delta H$ but does that mean that $q$ is a $+q$. Vice versa for a endothermic reaction. I get confused on which sign i should use for which when i do my thermochemistry questions.

2. Nov 23, 2014

### Staff: Mentor

For an exothermic reaction at constant temperature and pressure, ΔH = q, and both are negative. For an endothermic reaction at constant temperature and pressure, ΔH = q, and both are positive.

Chet