Calculating Enthalpy Changes

Finding them out in a lab -

• To measure the enthalpy change, you need to know 2 things: Moles of the stuff that is reacting, and the change in temperature

The experiment -

• The experiment varies with the type of reaction. Some reactions just take place in a beaker with a thermometer. It is best to use a polystyrene beaker so no heat is lost or gained by the beaker
• Combustion reactions are different, as the reactant is burned in air. A copper calorimeter containing a known mass of water is used. You burn a known mass of reactant and record the temperature change

Q = mcΔT

Q - Heat lost/gained (same as enthalpy change if heat/pressure is constant)

m - Mass of water in the calorimeter, or solution in the polystyrene beaker

c - Specific Heat Capacity of water (4.18)

ΔT - Change in temperature of the water/solution

Remember when calculating any standard enthalpies, it is for 1 mole!!

So if it says for 2 or 3 moles, just multiply your answer by the number of moles required