The Goal: Calorimetry is the study of how the heat lost by one body is gained by another. Early studies of heat defined it as a 'caloric fluid'; and heat does seem to flow. We have borrowed the term calorie to define a quantity of heat energy: 1cal = 4.2J. (1000 calories is 1 Calorie, the kind we eat). You will use calorimetry to predict the temperature of a mixture.
The Method: Hot water will be mixed with cold water. You will predict mathematically the final temperature, then check it experimentally.
The Theory: It is a basic law of thermodynamics that heat flows from high temperatures to low tempertures. Therefore, if a substance at a high temperature is mixed with something cooler, the hotter object cools and the cooler object heats up. To understand how an object has heat we must define a quantity called the Specific Heat Capacity: c. It is a quantity that a substance possess, like weight, color, or hardness. Substances like water have very high specific heats while air has a very low c. One uses a hot water bottle, not a hot air bottle, to warm one's feet on a cold night.
There is a math equation which uses c and mass to find the energy necessary to raise or lower the temperature of something. It goes like this:
Q = mc (Tf - Ti)
Q is heat (don't ask me why). The mass is m, Ti is the starting temperature, and Tf is the temperature of the object after heat is added or removed. For instance, if the starting temperature is 20oC for 1kg of water, which has a specific heat of 1cal/gram Co, if you add 10 calories of heat the final temperature will be 30oC.
Using the idea that heat flows from how to cold and this equation:
mc (Th - Tf) = mc (Tf - Tc)
heat lost = heat gained
one can predict the final temperature of a mixture. The Tf is the same for both, but Ti is different for each substance in your experiment, the hot and cold temperatures, respectively. Predict means to do the math before the experiment, not consult the Psychic Friends Hotline!
One source of error with this kind of experiment is that some heat leaks out of the mixture container before it can warm up the cooler substance.
|Click this button to continue:|