Most chemistry is done under conditions of constant pressure or constant volume (e.g. all of your body chemistry occurs at about atmospheric pressure - no pressure changes occur within single cells doing chemistry). Thus it is convenient to define a term for the heat involved in processes occurring with no change in pressure:
Calorimetry is the science of measuring heat. It is particularly useful because under two readily achievable laboratory conditions heat = E.
Heat is a measure of energy transferred between objects of different temperatures. We are already familiar with the units of temperature, what are the units of heat?
Specific Heat is the amount of heat it takes to raise 1 g of a specific substance 1 °C. Specific heats for other substances are relative to water, so no units (comparing results in canceling out units).
The heat transferred in a process (q) is summarized in the equation:
where m is the mass of substance and Csp is the specific heat of the substance.
Example: 750 calories of heat is transferred to 100.0 g of water at 20.00 °C. What will the new temperature of the water be assuming no heat is lost to the container or the surroundings?
Known: heat capacity of water = 1 cal / (g°C) [assume exact for problem]; q = mCspT
Adding the difference to the original temperature gives: 20.00 °C + 7.50 °C = 27.50 °C = 27.5 °C
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© R A Paselk
Last modified 6 March 2015