Uploaded August 2025 | Updated September 2026, 2 weeks ago
Heat Capacities
Heat Capacity and Units
Heat capacity is the ability of an object to store heat.
An object’s mass and specific heat primarily influence its heat capacity.
It is typically measured in joules per gram (J/g) or kilojoules per mole (kJ/mol).
Heat of Fusion (Melting)
Heat of fusion- is the amount of energy required to change a unit mass of a substance from a solid to a liquid at its melting point, without changing its temperature.
The energy is used to break molecular bonds during the phase transition and do not increase the temperature.
Referred to as latent heat
Heat of Crystallization (Freezing)
Heat of crystallization- the amount of heat energy released or absorbed when a substance transitions from a liquid (or sometimes a gas) to a solid crystalline state.
Melting and Freezing Opposite but Equal
Since melting and freezing are opposite changes, the amount of energy absorbed to melt a solid is equal to the amount of energy removed to freeze a liquid of equal mass
The heat of crystallization (freezing) is generally equal in magnitude but opposite in sign to the heat of fusion (melting)
Example, when water freezes into ice, it releases heat (an exothermic process), and the heat of crystallization for water is approximately -334 J/g (or -6.01 kJ/mol), meaning 334 J of energy is released per gram of water as it crystallizes.
Heat of Vaporization (Boiling)
Heat of Vaporization- the amount of heat energy required to convert a substance from a liquid to a gas (or vapor) at a constant temperature, typically at its boiling point.
This energy is needed to overcome the intermolecular forces holding the liquid molecules together, allowing them to transition into the gaseous state.
Example, the heat of vaporization for water at 100°C is approximately 2257 J/g (or 40.7 kJ/mol), meaning 2257 J of energy is required to vaporize one gram of water into steam.
Heat of Condensation
Heat of condensation- the amount of heat energy released when a substance transitions from a gas (or vapor) to a liquid at a constant temperature.
Example, for water at 100°C, the heat of condensation is approximately -2257 J/g (or -40.7 kJ/mol), meaning 2257 J of energy is released per gram of water vapor as it condenses into liquid water.
Equal but Opposite
Since vaporizing and condensing are opposite changes, the amount of energy absorbed to boil a liquid is equal to the amount of energy removed to condense a gas of equal mass.
Link to Lecture Slides: drive.google.com/file/d/15k8BP7RhZ3i-Mm9Oi6LnBjfa5f5Qr9Ls/view?usp=drive_link
*Due to the description character limit the full work cited for "Heat Capacities" can be viewed at... docs.google.com/document/d/1H0JjWuhRqe1YuW2LEak2z8y-cGRrW22l/edit?usp=drive_link&ouid=104237452697237972847&rtpof=true&sd=true
Heat Capacities
Heat Capacity and Units
Heat capacity is the ability of an object to store heat.
An object’s mass and specific heat primarily influence its heat capacity.
It is typically measured in joules per gram (J/g) or kilojoules per mole (kJ/mol).
Heat of Fusion (Melting)
Heat of fusion- is the amount of energy required to change a unit mass of a substance from a solid to a liquid at its melting point, without changing its temperature.
The energy is used to break molecular bonds during the phase transition and do not increase the temperature.
Referred to as latent heat
Heat of Crystallization (Freezing)
Heat of crystallization- the amount of heat energy released or absorbed when a substance transitions from a liquid (or sometimes a gas) to a solid crystalline state.
Melting and Freezing Opposite but Equal
Since melting and freezing are opposite changes, the amount of energy absorbed to melt a solid is equal to the amount of energy removed to freeze a liquid of equal mass
The heat of crystallization (freezing) is generally equal in magnitude but opposite in sign to the heat of fusion (melting)
Example, when water freezes into ice, it releases heat (an exothermic process), and the heat of crystallization for water is approximately -334 J/g (or -6.01 kJ/mol), meaning 334 J of energy is released per gram of water as it crystallizes.
Heat of Vaporization (Boiling)
Heat of Vaporization- the amount of heat energy required to convert a substance from a liquid to a gas (or vapor) at a constant temperature, typically at its boiling point.
This energy is needed to overcome the intermolecular forces holding the liquid molecules together, allowing them to transition into the gaseous state.
Example, the heat of vaporization for water at 100°C is approximately 2257 J/g (or 40.7 kJ/mol), meaning 2257 J of energy is required to vaporize one gram of water into steam.
Heat of Condensation
Heat of condensation- the amount of heat energy released when a substance transitions from a gas (or vapor) to a liquid at a constant temperature.
Example, for water at 100°C, the heat of condensation is approximately -2257 J/g (or -40.7 kJ/mol), meaning 2257 J of energy is released per gram of water vapor as it condenses into liquid water.
Equal but Opposite
Since vaporizing and condensing are opposite changes, the amount of energy absorbed to boil a liquid is equal to the amount of energy removed to condense a gas of equal mass.
Link to Lecture Slides: drive.google.com/file/d/15k8BP7RhZ3i-Mm9Oi6LnBjfa5f5Qr9Ls/view?usp=drive_link
*Due to the description character limit the full work cited for "Heat Capacities" can be viewed at... docs.google.com/document/d/1H0JjWuhRqe1YuW2LEak2z8y-cGRrW22l/edit?usp=drive_link&ouid=104237452697237972847&rtpof=true&sd=true
