Heating and Cooling Curves of Pure Substances
Heating Curve of a Pure Substance
* As the temperature increases, potential
energy changes to kinetic energy
Graph
Explanation
Section
*pure solid has an increase in temperature
A-B
Q = mc∆T (∆T= Tfinal - Tinitial)
*phase change; solid changing to liquid
B-C
*melting point; this is the temperature at
which the pure substance will melt
∆H = mHf (Hf is the heat of fusion)
*pure liquid has an increase in temperature
C-D
Q = mc∆T
*phase change; liquid changing to gas
D-E
*boiling point; this is the temperature at
which the pure substance will boil
∆H = mHv (Hv is the heat of vaporization)
*pure gas has an increase in temperature
E-F
Q = mc∆T
∆H and Q both represent energy in either the unit
ofcalories or Joules
Cooling Curve of a Pure Substance
* As the temperature decreases, kinetic energy
changes to potential energy
Graph
Explanation
Section
*pure gas has a decrease in temperature
P-Q
Q = mc∆T (∆T= Tfinal - Tinitial)
*phase change; gas changing to liquid
Q-R
*condensation point; this is the
temperature at which the pure substance
will condense from a gas to a liquid (same
temperature as when it boils)
∆H = mHv (Hv is the heat of vaporization)
*pure liquid has a decrease in temperature
R-S
Q = mc∆T
*phase change; liquid changing to solid
S-T
*freezing point; this is the temperature at
which the pure substance will freeze (same
temperature as when it melts)
∆H = mHf (Hf is the heat of fusion)
*pure solid has a decrease in temperature
E-F
Q = mc∆T
∆H and Q both represent energy in either the unit
ofcalories or Joules