Heat Flow
• Whenever there is a temperature difference between two objects in contact, heat energy will flow from the warmer object to the cooler object until they reach the same temperature.

• If there is no phase change in the substance, the heat energy that flows out of or into a substance can be expressed as:

 Q = Amount of Heat flowing into or out of one of the substances in contact (SI: J, Other: cal) > 0 Heat flows into the substance < 0 Heat flows out of the substance m = mass of the substance (SI: kg, other: g) c = Specific Heat Capacity of the substance (SI: J/kg/ oC, other: cal/g/ oC) ΔT = T f - T o = Change in Temperature of a substance (SI: K or oC)

Whenever a substance changes phases the heat energy that flows out of or into a substance no longer depends upon a temperature change:

Latent Heat Of Vaporization: ((liquid - gas transitions)

Qv = ± m Lv

 Lv = Heat of Vaporization (SI: J/kg, other: cal/g) = Amount of heat energy necessary to change the phase of a unit mass of a substance from a Liquid to a Vapor or visa versa. Q > 0 Positive if the substance boils/vaporizes Q < 0 Negative if the substance condenses/liquidifies

Latent Heat Of Fusion: (solid - liquid transitions)

Qf = ± m Lf

 Lf = Heat of Fusion (SI: J/kg, other: cal/g) = Amount of heat energy necessary to change the phase of a unit mass of a substance from a Solid to a Liquid or visa versa. Q > 0 Positive if the substance melts Q < 0 Negative if the substance freezes

Table of Values: