Measuring Enthalpy Changes

What is the equation for the amount of heat energy transferred (q)?

q = mcΔT

m= mass of the solution in the calorimeter

c= specific heat capacity of solution

ΔT= temperature change

What assumptions do we make when calculating the heat energy transferred?

• All the heat is just exchanged with the solution.

• The solution has the same specific heat capactiy as water.

• The density of the solution is 1 g cm-3 (so the mass is always the same as the final volume in the calorimeter).

What is the specific heat capacity of water?

4.18 Jg-1K-1.

How can you calculate the enthalpy change using “q”?

Enthalpy change= q/ number of moles

What is enthalpy change measured in?

kilojoules per mole (kJ mol^-1).

∴ q must be divided by 1000 when being used to calculate enthalpy change.

Why are enthalpy change values found using calorimetry never completely accurate?

• Heat is easily lost to the surroundings.