is molar enthalpy affected if the system is a solid rather than a liquid
Yes, the molar enthalpy of a substance can be affected by the state of matter, such as whether it is a solid or a liquid. The molar enthalpy is a measure of the energy stored in a substance, typically represented as ΔH (delta H), and is expressed in units of energy per mole (such as joules per mole).
When a substance transitions from one state to another (e.g. from solid to liquid or from liquid to gas), it undergoes a physical change, and this change affects the molar enthalpy.
In order to determine the molar enthalpy change during a phase transition, you can use the equation:
ΔH = q / n
where ΔH is the molar enthalpy change, q is the heat transferred, and n is the number of moles of the substance.
When a solid undergoes a phase change to become a liquid, such as melting, energy is required to break the intermolecular forces holding the solid together. This energy is known as the heat of fusion. The molar enthalpy of fusion (ΔHfus) represents the amount of energy needed to convert one mole of a solid substance to one mole of a liquid substance at constant temperature and pressure.
Once a substance is in the liquid state, further energy input may be required to convert it to a gas phase. This energy is known as the molar enthalpy of vaporization (ΔHvap). It represents the amount of energy required to convert one mole of a liquid substance to one mole of a gas substance at constant temperature and pressure.
Therefore, the molar enthalpy of a substance (solid or liquid) will differ due to the energy required for a phase transition to occur.