Heat capacity measures the amount of energy needed to raise a body's temperature by one degree. Finding the heat capacity of a material is reduced to a simple formula: just divide the heat exchanged between the body and the environment by the temperature difference, so as to obtain the energy per degree. Each existing material has its own specific heat capacity.
Formula: heat capacity = (heat exchanged) / (temperature difference)
Steps
Part 1 of 2: Calculating the Thermal Capacity of a Body
Step 1. Learn the heat capacity formula
To know this characteristic of a material it is enough to divide the quantity of energy supplied (E) by the temperature difference generated (T). According to this definition, our equation is: heat capacity = E / T.
- Example: an energy of 2000 J (joules) is required to raise the temperature of a block by 5 ° C. What is the heat capacity of the block?
- Thermal capacity = E / T.
- Thermal capacity = 2000 J / 5 ° C.
- Thermal capacity = 500 J / ° C (joules per degree Celsius).
Step 2. Find the temperature difference for variations of several degrees
For example, if you want to know the heat capacity of a body to which an energy of 60 J must be applied to generate a temperature increase from 8 ° C to 20 ° C, then first you need to know the temperature difference. Since 20 ° C - 8 ° C = 12 ° C, you know that the body temperature has changed by 12 ° C. Proceeding:
- Thermal capacity = E / T.
- Body heat capacity = 60 J / (20 ° C - 8 ° C).
- 60 J / 12 ° C.
- Body heat capacity = 5 J / ° C.
Step 3. Use the correct units of measurement to make problem solutions make sense
A heat capacity of 300 is meaningless if you don't know how it was measured. Heat capacity is measured in energy per degree. Since the energy is expressed in joules (J) and the temperature difference in degrees Celsius (° C), then your solution indicates how many joules are needed to generate a temperature difference of one degree Celsius. For this reason your answer must be expressed as 300 J / ° C, or 300 joules per degree Celsius.
If you have measured energy in calories and temperature in kelvins, then your answer will be 300 cal / K
Step 4. Remember that this formula is also valid for the cooling process of bodies
When an object becomes 2 degrees colder, it loses the same amount of heat it would acquire if its temperature were raised by 2 degrees. For this reason, if the physics problem requires: "What is the heat capacity of an object that loses 50 J of energy and lowers its temperature by 5 ° C?", Then your answer will be:
- Thermal capacity: 50 J / 5 ° C.
- Thermal capacity = 10 J / ° C.
Part 2 of 2: Using the Specific Heat of a Material
Step 1. Know that specific heat is the amount of energy needed to raise the temperature of a gram of material by one degree
When you know the heat capacity of an object's unit of mass (1 gram, 1 ounce, 1 kilogram, and so on), then you have found the specific heat of the material. Specific heat indicates how much energy is needed to increase a unit of material by one degree. For example, 0.417 J are needed to raise the temperature of a gram of water by one degree Celsius. For this reason, the specific heat of water is 0.417 J / ° Cg.
The specific heat of a material is a constant value. This means that all pure water always has a specific heat of 0.417 J / ° Cg
Step 2. Use the heat capacity formula to find the specific heat of the object
It is not a difficult procedure, just divide the final answer by the mass of the body. The result will tell you how much energy is needed for each unit of mass of the material - for example, how many joules it takes to change 1g of ice by 1 ° C.
- Example: "I have 100 g of ice. It takes 406 J to raise its temperature by 2 ° C, what is the specific heat of ice?" '
- Heat capacity per 100 g of ice = 406 J / 2 ° C.
- Heat capacity per 100 g of ice = 203 J / ° C.
- Heat capacity for 1 g of ice = 2, 03 J / ° Cg.
- If in doubt, think in these terms: It takes 2.03 J of energy to raise the temperature of just one gram of ice by one degree Celsius. So, if you have 100 g of ice, you will have to multiply the energy by 100 times.
Step 3. Use specific heat to find the energy needed to increase the temperature of any material by several degrees
The specific heat of a material expresses the amount of energy needed to increase a unit of matter (usually 1 g) by one degree Celsius. To find the heat needed to increase any object by a certain number of degrees, just multiply all the data together. Energy needed = mass x specific heat x temperature change. The product must always be expressed according to the unit of measurement of energy, usually in joules.
- Example: if the specific heat of aluminum is 0, 902 J / ° Cg, how much energy is needed to increase the temperature of 5 g of aluminum by 2 ° C?
- Energy required: = 5g x 0, 902 J / ° Cg x 2 ° C.
- Energy required = 9.2 J.
Step 4. Learn the specific warmth of different commonly used materials
For practical help, it is worth learning the specific heat values of many materials that are used in test examples and physics assignments, or that you will come across in real life. What lessons can you draw from this data? For example, you may notice that the specific heat of metals is much lower than that of wood, which means that a metal spoon heats up faster than a wooden one when you forget it in a cup of hot chocolate. A low specific heat value indicates faster temperature changes.
- Water: 4, 179 J / ° Cg.
- Air: 1.01 J / ° Cg.
- Wood: 1.76 J / ° Cg.
- Aluminum: 0, 902 J / ° Cg.
- Gold: 0, 129 J / ° Cg.
- Iron: 0, 450 J / ° Cg.
Advice
- In the International System, the unit of measurement of heat capacity is the joule per kelvin, and not just the joule.
- The temperature difference is represented with the Greek letter delta (Δ) also in the unit of measurement (for which it is written 30 ΔK and not just 30 K).
- Heat (energy) must be expressed in joules according to the International System (highly recommended).
