Question

Foam cup A has 36 mL of water that contains 2 moles of HCl at 20 degrees Celsius. Foam cup B has 36 mL of water that contains 2 moles of NaOH at 20 degrees Celsius. The contents of foam cup A are added to foam cup B and a chemical reaction occurs. The final temperature of the contents of cup B is 31 degrees Celsius. I need to calculate the enthalpy change of the reaction. The density of both solutions is 1 g/mL.

Answer 1

The total mass of the solutions = 1 x (36 + 36) = 72 g
Assuming the heat capacity of the solutions to be same as that of water, it is 4.186 J/g K

The heat released by the reaction is equal to the heat absorbed by the water. Thus:
Q = mCpΔT
Q = 72 x 4.186 x (31 - 20)
Q = 3,315 J
The moles of reactant added were 2 each, so the enthalpy change of reaction is:
ΔH = 3,315 / 2

ΔH = 1,660 Joules per mole