Heat Capacity
Definition and meaning of Heat Capacity in chemistry.
Heat capacity is the total heat energy required to raise a sample's temperature by one degree. It is classified as an extensive physical property in the field of thermodynamics. This means the value changes depending on the size or mass of the object being heated.
In more detail
A massive bucket of water requires much more heat to warm up than a tiny cup. This happens because the large bucket has a much larger total heat capacity. Chemists calculate this using a simple equation where heat equals heat capacity times the temperature change.
Because total heat capacity scales with the size of the sample, scientists usually prefer different metrics. They use specific heat capacity to describe the heat needed for exactly one gram of a substance. They use molar heat capacity to describe the heat needed for exactly one mole.
These standard measurements allow chemists to compare totally different materials fairly. For example, solid metals generally have a very low specific heat capacity. This explains why a heavy iron pan gets burning hot very quickly on a hot stove.
Water has a very high specific heat capacity, so it takes much longer to boil. Heat capacity also depends on the exact physical conditions during the heating process. Heating a gas at a constant pressure allows the gas to expand its volume.
Some absorbed energy does the physical work of pushing against the surrounding air. Therefore, constant pressure heat capacity is usually larger than constant volume heat capacity.
Key facts
| Standard Symbol | C |
|---|---|
| SI Unit (Total) | J/K |
| SI Unit (Specific) | J/(g·K) |
| Key Equation | q = CΔT |
| Property Type | Extensive (depends on mass) |
Liquid water has a high specific heat capacity of 4.18 J/(g·K). Heating a 250 gram cup of water from 20 °C to 30 °C requires a lot of energy. We calculate the heat using q = mcΔT, which is 250 g × 4.18 J/(g·K) × 10 K. The total energy required to heat the water is exactly 10,450 joules.
Frequently asked questions
What is the difference between total heat capacity and specific heat capacity?
Total heat capacity applies to an entire object, like a whole frying pan. Specific heat capacity measures the energy needed for just one gram of that pan's metal.
Why does water take so long to boil on a stove?
Liquid water has an unusually high specific heat capacity. It must absorb a massive amount of thermal energy from the burner just to raise its temperature a few degrees.
Why do gases have two different heat capacities?
Heating a gas at constant pressure lets it expand and do physical work. This extra work requires more heat than keeping the gas trapped in a constant volume.