Heat is the energy transferred to a body during heating or taken from a body during cooling. Heat is a physical quantity that characterizes the transfer of thermal energy from one thermodynamic system to another.
$$Q=cm \Delta T$$
where,
c— specific heat of the substance;
m— mass of the body;
ΔT— temperature change.
The unit of heat in the International System of Units (SI) is the joule. The joule is named after the English physicist James Prescott Joule.
Melting is the phase transition from a solid state to a liquid state, and solidification is the reverse transition. Each substance has a specific temperature – melting point, at which it changes from a solid to a liquid state. The substance solidifies at the same temperature at which it melts.
The amount of energy required for melting/solidification (heat Q) is proportional to the mass of the body (m) and depends on the material of the body:
$$Q=\pm \lambda m$$
where,
λ— latent heat of fusion (J/kg);
m— mass of the substance (kg).
NOTE! Use a plus sign in the formula when describing melting and a minus sign when describing solidification.
Vaporization is the phase transition from a liquid state to a gaseous state, and condensation is the reverse transition. Different substances have different boiling points. The boiling temperature depends on the pressure exerted by the atmosphere (air pressure) – the higher the pressure, the higher the boiling temperature of the liquid.
The amount of energy required for vaporization/condensation (heat Q) is proportional to the mass of the body (m) and depends on the material of the body:
$$Q=\pm Lm$$
where,
L— latent heat of vaporization (J/kg);
m— mass of the substance (kg).
NOTE! Use a plus sign in the formula when describing vaporization and a minus sign when describing condensation.