Calorimetry
Calorimetry is the study of heat flow and heat measurement. Calorimetry experiments determine the heat changes of reactions by making accurate measurements of temperature changes within a calorimeter. Calorimeters are devices that are designed to maintain the heat in the device. Most calorimeters are double insulated, but for most purposes, a Styrofoam cup with a Styrofoam lid can be used.
Specific Heat
A common misconception is that heat energy and temperature are the same thing. They are not. Temperature is a measurement of how fast the particles of a substance are moving. Heat energy causes the molecules to move faster, and can affect the temperature. However, if you expose the same amount of heat energy to two different substances, the temperature of one substance may change temperature faster than the other. Let's talk an example.
On a hot, sunny day, a person may walk outside and notice that the pavement is a lot warmer than the grass will be. This difference is caused by the specific heat of the two substances. The pavement required less energy to heat up a given mass than the same mass of grass requires. Therefore, the specific heat of the pavement is lower than that of the grass. The temperature increases depends on the specific heat of the material. The specific heat tells how much heat is required to increase the temperature of 1 gram of a material by 1 degree Celsius.
A substance with a low specific heat, like aluminum, will heat up very rapidly. It takes very little energy to increase 1 gram of aluminum by 1 degree Celsius. A substance with a high specific heat, like Styrofoam, will heat up very slowly. It takes a lot of energy to increase 1 gram of Styrofoam by 1 degree Celsius. That works the other way, too. Since Styrofoam has a high specific heat, it will not cool down easily either. You will have to pull a lot of energy out of the Styrofoam in order for the temperature to go down by 1 degree Celsius.
Since every substance has its own specific heat, you will need to know the specific heats of the material in order to calculate the heat. Below is listed the specific heat of a few common substances in chemistry. The only one you will need to know is water.
Specific Heat
A common misconception is that heat energy and temperature are the same thing. They are not. Temperature is a measurement of how fast the particles of a substance are moving. Heat energy causes the molecules to move faster, and can affect the temperature. However, if you expose the same amount of heat energy to two different substances, the temperature of one substance may change temperature faster than the other. Let's talk an example.
On a hot, sunny day, a person may walk outside and notice that the pavement is a lot warmer than the grass will be. This difference is caused by the specific heat of the two substances. The pavement required less energy to heat up a given mass than the same mass of grass requires. Therefore, the specific heat of the pavement is lower than that of the grass. The temperature increases depends on the specific heat of the material. The specific heat tells how much heat is required to increase the temperature of 1 gram of a material by 1 degree Celsius.
A substance with a low specific heat, like aluminum, will heat up very rapidly. It takes very little energy to increase 1 gram of aluminum by 1 degree Celsius. A substance with a high specific heat, like Styrofoam, will heat up very slowly. It takes a lot of energy to increase 1 gram of Styrofoam by 1 degree Celsius. That works the other way, too. Since Styrofoam has a high specific heat, it will not cool down easily either. You will have to pull a lot of energy out of the Styrofoam in order for the temperature to go down by 1 degree Celsius.
Since every substance has its own specific heat, you will need to know the specific heats of the material in order to calculate the heat. Below is listed the specific heat of a few common substances in chemistry. The only one you will need to know is water.
Substance
water
nitrogen gas aluminum iron copper mercury gold sodium chloride ethanol ammonia |
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Calculating Heat
The equation for finding the amount of heat lost or gained by an object is:
The equation for finding the amount of heat lost or gained by an object is:
q=mcΔT
In this equation,
q stands for the heat lost or gained, measured in Joules (J)
m is the mass of the material, measured in grams (g)
c is the specific heat of the material, measured in J/g OC
ΔT is the change in temperature of the material (final temp - initial temp), measured in degrees Celsius (OC)
q stands for the heat lost or gained, measured in Joules (J)
m is the mass of the material, measured in grams (g)
c is the specific heat of the material, measured in J/g OC
ΔT is the change in temperature of the material (final temp - initial temp), measured in degrees Celsius (OC)
Example 1: A 12.2 g piece of aluminum at 100 OC is placed in a calorimeter with 50 g of water at 20 OC. The metal piece heats up the water to 24 OC. What amount of heat was gained by the water?
Answer: q = ?, m = 50 g, c = 4.184 J/g OC, ΔT = 24 - 20 = 4 OC
Answer: q = ?, m = 50 g, c = 4.184 J/g OC, ΔT = 24 - 20 = 4 OC
q = 50(4.184) 4
q = 836.8 J
q = 836.8 J
Example 2: How much heat was lost by the aluminum?
Answer: By the law of conservation of energy, the heat that warmed the water must have come from the metal. Therefore, the metal must have lost the same amount of energy that the water gained. So the heat for the aluminum must be q = -836.8 J. The value is negative to indicate the energy was lost.
Answer: By the law of conservation of energy, the heat that warmed the water must have come from the metal. Therefore, the metal must have lost the same amount of energy that the water gained. So the heat for the aluminum must be q = -836.8 J. The value is negative to indicate the energy was lost.
The heat lost by one object is equal to the heat gained by the other object. or q1 = -q2
Example 3: What is the specific heat of the aluminum?
When the hot aluminum is placed in the water, the aluminum will cool down. The aluminum will end up at the same temperature as the water. So, the final temperature of the aluminum will be 24OC.
Answer: q = -836.8, m = 12.2 g, c = ? J/g OC, ΔT = 24 - 100 = -76 OC
Answer: q = -836.8, m = 12.2 g, c = ? J/g OC, ΔT = 24 - 100 = -76 OC
-836.8 = 12.2(c)-76
c = 0.902 J/gOC
c = 0.902 J/gOC