Here's a video on heat capacity (15 min) (note that fusion actually means melting, not solidifying): Khan Academy: Specific Heat, Heat of Fusion and Vaporization, on YouTube
Here's a video on calorimetry and Hess' Law(12 min): CrashCourse Chemistry: Calorimetry, on YouTube
If you want to measure ΔH, you usually use calorimetry, which just means measuring heat. The usual way this is done is by measuring how much the temperature of a system increases when the process occurs. For instance, perhaps we have 2 solutions (like an acid and a base solution) and we mix them in a thermos. We measure the temperature of the solutions before mixing and also after the reaction. Because we run the reaction in a thermos, we expect that almost all the heat from the reaction will stay in the thermos. Also, we don't close the thermos all the way, so the pressure is always atmospheric pressure. The reaction enthalpy is related to the temperature change, but how, exactly?
Heat capacity tells us how much heat is needed to increase the temperature of an object or substance by a certain amount. The unit calorie is the energy needed to increase the temperature of 1g of water by 1 degree (either Celsius or Kelvin). 1 calorie = 4.18 J. Generally, the heat capacity is
| C = | q |
| ΔT |
| C = | q |
| ΔT x m |
First, you need to be a little careful about whether the experiment was done at constant pressure or constant volume. This will determine whether you calculate enthalpy or internal energy of reaction. Second, make sure you figure out the heat capacity of the system correctly. You might have to add up heat capacities of different parts of the system using (mass x specific heat) or (moles x molar heat capacity) of each part. Once you've figured that out, you can usually think of it as a "unit conversion" and use dimensional analysis to combine all the quantities you know to find the quantity you want.