Thermal Physics: Heat Capacity

In Britain's own peculiar way it is bloody freezing, in the middle of June. So, what better time than now to do a little something on thermal physics.

As with most physics, this all comes down to energy, and the transfer, exchange and general movement of same. The effect of this is generally kind of obvious. The more thermal energy something has, the larger it's temperature is. What's interesting is that various materials have a greater inclination to be heated that others. This is easier demonstrated. Find a metal surface, and consider it's temperature. Unless you already know what I'm about to get at and are purposefully being difficult by considering the inside of an oven, you should agree that said metal is at room temperature. Now if you touch said metal, you should notice that it is quite cold. "Gosh James, how can this be?" I hear you ask. Well, as we all know, heat tends to flow to colder areas. Things like to reach an equilibrium, that's just they way of things. So when you touch metal, you aren't feeling cold metal as much as you are feeling the heat energy in your fingers being SUCKED OUT FROM YOUR BODY.

Dramatic reconstruction

The way we measure how willing objects are to drain the life from your very body is called the specific heat capacity, c. This is defined as the energy required to cause a temperature rise of 1K per unit mass, usually 1 kg. From it we can work out a bunch of stuff with the equation:

ΔQ = mcΔT

In words, the change in thermal energy of an object is equal to the mass by the SHC by the change in temperature. T is measured in kelvins really but given that 1 K and 1 °C is exactly the same it doesn't really matter once you stick that Δ there.

All important equations are given to you but I feel it's helpful to get to know them beforehand. So let me throw this one at you:

 ΔQ = ml

This is where we bring in latent heat, l. Again this comes with a "specific" alternative. Two actually, and as such we have two definitions to remember. Both are pretty similar however, so I don't imagine you will have too much trouble.
Specific latent heat of fusion

the energy required to chance 1 kg of solid into 1kg of liquid, with no change in temperature.

Specific latent heat of vaporisation

the energy required to change 1 kg of liquid into 1 kg of gas with no change in temperature.

What this means for you is that when working out the energy required to  get a substance from one temperature to another, and there is a state change in between, you are going to need to make more than one calculation. One for the first temperature increase, one for the state change, then another for any further temperature increase. Keep yourself aware of this and you should be fine.

On the practicality side of things, this area of physics is widely used, mainly in the area of cooling, by dissipating thermal energy. It can been seen in power stations, and closer to home, us when we sweat.

Continue into the world of ideal gases