Lab Overview Investigation #16: "Heat Storage for Solar Heating"

Definitions

Heat Capacity - amount of energy necessary to raise the temperature of a gram of substance one degree celsius.

Specific Heat of Crystallization or Solidification - amount of energy lost to bring about that change of state in one unit mass

Calorimeter Constant - amount of energy needed to raise the temperature of the calorimeter one degree celsius.
 

To use a calorimeter, you must first determine the calorimeter's constant. To do this, you must run an experiment with a known specific heat. In this experiment, you used the loss of heat by boiling water. Some of the heat lost by the boiling water is transferred to the room temperature water already in the calorimeter resulting in an increase in the temperature of the water inside the calorimeter. Not all of the heat is transferred to the water however. Some of it is transferred to the calorimeter itself. By comparing the amount of heat gained by the water inside the calorimeter with the amount of heat that the water inside the calorimeter should have gained, the amount of heat gained by the calorimeter can be found.

With this, you can then find the calorimeter constant. Again, the only reason you can do this is because we already know the specific heat of water.

T_rt = temperature of room temp. water

m_b = mass of boiling water

C_w = specific heat of water

m_rt = mass of room temperature water

T_b = temperature of boiling water

T_{max =} obtained from graph
 
 

Now that you have determined the calorimeter constant, you can use the calorimeter to find for example, the specific heat of solidification for sodium thiosulfate pentahydrate. A molten solution of sodium thiosulfate pentahydrate is added to the calorimeter. This molten solution is seeded with a small crystal which is small enough not to affect the total mass of the salt greatly. The times and temperatures are again recorded. A graph is drawn and T_max determined.
 
 

m_w = mass of water in the calorimeter

C_w = specific heat of water

T_{max =} obtained from graph

T_cw = temperature of water in the calorimeter before the vial of salt was added

K = calorimeter constant

m_salt = mass of salt
 
 

When comparing specific heats of solidification, the amount of energy per gram is important but also the melting point range. It is useful to compare materials by energy per gram because it reflects energy/volume. In other words it is also important to know how much energy can be stored in how much space.

You can equate energy lost with energy gained but only if you realize and take into consideration the fact that the values have opposite signs. Energy lost is a negative = Energy gained which is a positive. Here the signs don't work out so you have to add a negative to one side or take the absolute values of both.