Heat Capacity
Definition and meaning of Heat Capacity in chemistry.
Heat capacity is the amount of heat energy required to raise the temperature of a given amount of a substance or system by one degree (kelvin or Celsius). It is an extensive property, meaning it depends on the size or amount of the sample being heated.
In more detail
Heat capacity is calculated from q = CΔT, where q is heat absorbed or released and ΔT is the temperature change. Because it scales with sample size, chemists more often use specific heat capacity (heat capacity per gram) or molar heat capacity (per mole) to compare substances directly. Heat capacity also depends on conditions: at constant pressure (Cp) some absorbed heat does expansion work, so Cp is generally larger than heat capacity at constant volume (Cv) for gases.
Key facts
| Symbol | C |
|---|---|
| SI Unit | J/K (specific: J/(g·K); molar: J/(mol·K)) |
| Key Equation | q = CΔT |
| Field | Physical Chemistry |
Water has a specific heat capacity of 4.18 J/(g·K). Heating 250 g of water from 20°C to 30°C requires q = mcΔT = 250 g × 4.18 J/(g·K) × 10 K = 10,450 J.
Frequently asked questions
What is the difference between heat capacity and specific heat capacity?
Heat capacity applies to a whole object or sample and depends on its mass (extensive), while specific heat capacity is the heat capacity per gram of substance (intensive), allowing direct comparison between materials regardless of sample size.
Why is Cp usually greater than Cv for a gas?
At constant pressure, some of the absorbed heat goes into expanding the gas against its surroundings (doing work) rather than only raising its temperature, so more heat is needed per degree of temperature rise compared to constant volume.