Heat Capacity vs Specific Heat
When a substance is heated its temperature rises, and when it is cooled its temperature decreases. The difference in temperature is proportional to the amount of heat supplied. Heat capacity and specific heat are two proportionality constants to relate the temperature change and the amount of heat.
In thermodynamics, the total energy of a system is called internal energy. Internal energy specifies the total kinetic and potential energy of molecules in the system. Internal energy of a system can be changed either by doing work on the system or heating it. The internal energy of a substance increases when its temperature is increased. The amount of increase depends on the conditions in which heating takes place. Heat is required to increase the temperature. Heat capacity (C) of a substance is “the quantity of heat needed to raise the temperature of a substance by one degree Celsius (or one kelvin).” The heat capacity differ from substance to substance. The amount of substance is directly proportional to the heat capacity. That means by doubling the mass of substance, heat capacity can be doubled. The heat required to increase the temperature from t1 to t2 of a substance can be calculated using the following equation.
q= C x ∆t
q= required heat
The unit of heat capacity is JoC-1 or JK-1. Two types of heat capacities are defined in thermodynamics; the heat capacity at constant pressure and heat capacity at constant volume.
Heat capacity is dependent on the amount of substance. Specific heat or specific heat capacity (s) is the heat capacity, which is independent of the amount of substances. It can be defined as “the quantity of heat required to raise the temperature of one gram of a substance by one degree Celsius (or one Kelvin) at a constant pressure.” The unit of specific heat is Jg-1oC-1.The specific heat of water is very high with the value of 4.186 Jg-1oC-1. This means, to increase the temperature of 1 g of water by 1 oC, 4.186 J heat energy is needed. This high value encounters for the role of water in thermal regulation. To find the heat needed to increase the temperature of a certain mass of a substance from t1 to t2, following equation can be used.
q= m x s x ∆t
q= required heat
m= mass of the substance
However, above equation does not apply, if the reaction involves a phase change. For example, it does not apply when the water is going to the gas phase (at the boiling point), or when the water freezes to form ice (at the melting point). This is because; the heat added or removed during the phase change does not change the temperature.
What is the difference between Heat Capacity and Specific Heat?
- Heat capacity is the amount of heat needed to change a substances’ temperature by 1 oC or 1K. Specific heat is the heat needed to change 1g of substances’ temperature by 1 oC or 1K.
- Heat capacity is dependent on the amount of substance, but specific heat capacity is independent of it.