Heat Flow

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)
DT	= 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)

Q_v = ± m L_v

L_v	= 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)

Q_f = ± m L_f

L_f	= 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: