Latent Heat vs Sensible Heat
When the energy of a system changes because of a temperature difference between the system and its surroundings, we say that energy has been transferred as heat (q). Heat transfer takes place from high temperature to low temperature, which is according to a temperature gradient.
When a substance undergoes a phase change, the energy is absorbed or released as heat. Latent heat is the heat that is being absorbed or released from a substance during a phase change. This heat changes do not cause temperature changes as they are absorbed or released. A phase change means a solid going to the gaseous phase or a liquid going to a solid phase or vice versa. It is a spontaneous conversion and occurs at a characteristic temperature for a given pressure. So the two forms of latent heat are latent heat of fusion and latent heat of vaporization. Latent heat of fusion takes place during melting or freezing. And latent heat of vaporization takes place during boiling or condensing. The phase change releases heat (exothermic) when converting gas to liquid or liquid to solid. The phase change absorbs energy/ heat (endothermic) when going from solid to liquid or liquid to gas. For example, in the vapor state, water molecules are highly energetic. And there are no intermolecular attraction forces. They move around as single water molecules. Compared to this, liquid state water molecules have low energies. However, some water molecules are capable of escaping to the vapor state if they have high kinetic energy. At normal temperature, there will be equilibrium between the vapor state and liquid state water molecules. But, when heating at the boiling point, most of the water molecules will be released to the vapor state. So, when water molecules are evaporating, the hydrogen bonds between the water molecules have to be broken. For this, energy is needed, and this energy is known as the latent heat of vaporization. For water, this phase change occurs at 100°C (boiling point of water). However, when this phase change occurs at this temperature, heat energy is absorbed by water molecules, to break the bonds, but it will not increase the temperature more.
Specific latent heat means the amount of heat energy needed to convert a phase to another phase of a unit mass of a substance completely.
Sensible heat is a form of energy transferring during a thermodynamic reaction, which causes the temperature to change. The sensible heat of a substance can be calculated by the following formula.
Q = mc∆T
Q = sensible heat
M = mass of the substance
C = specific heat capacity
∆T= temperature change caused by the heat energy
What is the difference between Latent Heat and Sensible Heat?
• Latent heat does not affect the temperature of a substance whereas sensible heat affects the temperature and make it rise or decrease.
• Latent heat is absorbed or releases at a phase change. Sensible heat is the heat released or absorbed during any thermodynamic process other than phase changes.
• For example, when heating the water at 25°C to 100°C, the supplied energy caused a temperature increase. Therefore, that heat is called sensible heat. But when water at 100°C evaporates, it doesn’t cause a temperature rise. The heat absorbed at this moment is called the latent heat.