If a reaction causes 25.0 g of water to decrease temperature by 4.7 C at constant pressure, what is the change in enthalpy for the reaction? (The specific heat capacity of water is 4.184 J/g oC).

Question

If a reaction causes 25.0 g of water to decrease temperature by 4.7 ^oC at constant pressure, what is the change in enthalpy for the reaction? (The specific heat capacity of water is 4.184 J/g ^oC). Assume no heat transferred to surroundings.

Answer 1

q=mcΔt

q=25(4.184)(-4.7)

q= -491.62 J

For enthalpy change of reaction, you need to know more information, but that's the energy change. The reaction made the water colder, so:

-qwater=+qreaction

The reaction is endothermic, so the reaction absorbed 491.62 J (qrxn=+461.62J)