(EGY) Calculating Heat Energy Lesson
Calculating Heat Energy
Do all substances require the same amount of energy to increase in temperature? Think about the amount of energy required to boil water compared to the amount of energy needed to just make the pot hot. The pot becomes hot very quickly while it takes some time for the water to reach the same temperature. Why is this? Watch the video below to review the concepts of heat from our previous lesson as well as get us ready for understanding specific heat capacity.
As you have seen from watching the video, different substances have varying capacities for storing energy within their molecules. Heat energy can cause molecules to move about faster, increasing their random kinetic energy. An increase in this energy raises the temperature of the substance. Heat energy can also increase the vibrational or rotational energy of molecules, but this does not result in a temperature increase. Each substance has a unique specific heat capacity, meaning different substances have the ability to absorb only a certain amount of heat. Values for some common substances are shown in the table.
| Substance | Specific Heat for Some Common Substances (Numbers in J/ kg ° C) |
|---|---|
| Air (dry) | 1010 |
| Aluminum | 900 |
| Copper | 390 |
| Ethanol | 2450 |
| Glass | 840 |
| Ice (at -15°C) | 2000 |
| Mercury | 140 |
| Steel | 450 |
| Water (at 15°C) | 4190 |
Let's look at a comparison of water and copper. When the sample of water and copper are both heated by 1°C, the addition to the kinetic energy is the same. However, to achieve a temperature increase for water, a much larger proportional energy must be added to speed up the molecules of water. This means that the molecules of water are able to store the energy more readily before the energy transfers to the kinetic energy of making the molecules start moving. Remember, that temperature is a measure of the kinetic energy (how fast the molecules are moving). Therefore, the total energy required to increase the temperature of the water is much larger which means its specific heat is much larger.
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This relationship between heat and temperature change can actually be seen mathematically. The specific heat capacity is generally defined as the amount of heat energy required to raise the temperature of 1 kilogram of a substance by 1°C. It is a measure of how much heat energy a particular substance can hold. The units most commonly used are joules per gram per degree Celsius. The amount of heat energy that a substance gains or loses, Q, depends on the mass (m), the specific heat, (c), and the change in the temperature (∆T) of the substance. The formula for finding the heat energy is simply the product of the three factors, Q = mc∆T.
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