Why does an endothermic reaction cool an insulated chamber?

[madgab89]

Homework Statement

For the reaction 2H2O(l) -> 2H2(g)+O2(g) delta H = +571.5 kJ

If the reaction is carried out in an insulated chamber what effect would the reaction have on the temperature in the chamber? Why?

The attempt at a solution
I can't seem to get my head around this one. I know the sign on the enthalpy change is from the point of view of the system...but what really qualifies as the system and the surroundings if there is no real boundary between them?

 

[madgab89]

Wait...if I look at the equation
delta H=-CdeltaT

In order for delta H to be positive wouldn't temperature change have to be negative?

 

[Ygggdrasil]

A positive ΔH indicates that the reaction is endothermic; the reaction requires the absorption of heat in order to proceed. So, you are correct. The temperature will decrease because the reaction absorbs heat from its surroundings.