Question

here are three equations for heat calculations:
equation 1: $q = m\delta tc_{s.h}$.
equatoin 2: $q = n\delta h_{fus}$
equantion 3:$q = n\delta h_{vay}$
match the equation used to calculate the heat of the process described.
when the substance is going from a gas to a liquid
when the substance is being warmed up.
when the substance is being cooled down.
when the substance is going from a solid to a liquid
when the substance is going from a liquid to a gas.
when the substance is going from a liquid to a solid

Explanation:

• Equation 1: \( q = m\Delta Tc_{s.h.} \) is used for calculating the heat when there is a temperature change (warming up or cooling down) of a substance. \( m \) is mass, \( \Delta T \) is the change in temperature, and \( c_{s.h.} \) is the specific heat capacity.
• Equation 2: \( q = n\Delta H_{fus} \) is used for phase - change (fusion) when a substance goes from solid to liquid. \( n \) is the number of moles and \( \Delta H_{fus} \) is the enthalpy of fusion.
• Equation 3: \( q = n\Delta H_{vap} \) is used for phase - change (vaporization) when a substance goes from liquid to gas. Condensation (gas to liquid) and freezing (liquid to solid) are the reverse of vaporization and fusion respectively, but the same equations (with appropriate sign changes for heat release) can be conceptually related.

Answer:

• When the substance is going from a gas to a liquid: equation 3 (since condensation is the reverse of vaporization, and the same enthalpy concept for the phase - change between gas and liquid is involved).
• When the substance is being warmed up: equation 1.
• When the substance is being cooled down: equation 1.
• When the substance is going from a solid to a liquid: equation 2.
• When the substance is going from a liquid to a gas: equation 3.
• When the substance is going from a liquid to a solid: equation 2 (reverse of fusion, same enthalpy concept for the phase - change between solid and liquid).