Energy and
Physical Changes
– Part II
Heating Curves, Specific Heat Capacity, Molar
Heat, Calculations of Physical Energy Changes
Heating Curves
A. a graph that shows the temperature vs.
either time or energy
B. ENDOthermic heating curves
1. positive slope because heat is
absorbed
2. shows the transformation:
solid → liquid → gas
Heating Curves – Endothermic
A:
B:
↑ KE; PE constant
↑ PE; KE constant
C:
D:
E:
↑ KE; PE constant
↑ PE; KE constant
↑ KE; PE constant
Heating Curves
C. EXOthermic heating curves
1. negative slope because heat is released
2. shows the transformation:
gas → liquid → solid
Heating Curves – Exothermic
A:
B:
↓ KE; PE constant
↓ PE; KE constant
C:
D:
E:
↓ KE; PE constant
↓ PE; KE constant
↓ KE; PE constant
Specific Heat Capacity
A. the amount of heat necessary to convert
1 gram of a substance 1 °C
B. unit = cal/g x °C or J/g x °C
C. unique to each substance (and phase of substance)
 ex: specific heat capacity for liquid water =
4.18 J/g x °C; specific heat capacity for ice =
2.09 J/g x °C
D. symbol = c
E. H2O has the highest specific heat capacity among any
common substance
Molar Heat
A. Molar Heat of Fusion
1. the amount of heat necessary to melt (or
freeze) 1 mole of a substance at its melting
point
2. unique to each substance
3. symbol = ΔHfus
4. only applies when there is no temperature
change…describes potential energy and
NOT kinetic energy
Molar Heat
A. Molar Heat of Vaporization
1. the amount of heat necessary to evaporate
(or condense) 1 mole of a substance at its
boiling point
2. unique to each substance
3. symbol = ΔHvap
4. only applies when there is no temperature
change…describes potential energy and
NOT kinetic energy
Calculations of Energy Changes
A.
q = mcΔT
 used only for temperature changes!
1. q = the amount of heat absorbed or
released (in cal or J)
 a gain or loss of heat
 + q = heat absorbed = endothermic;
- q = heat released = exothermic
2. m = the mass of substance (in grams)
3. ΔT = the change in temperature
 Tfinal - Tinitial
Calculations of Energy Changes
B.
q = molΔHfus
 used only when the temperature is constant
1. q = the amount of heat absorbed or
released (in cal or J) for the substance
to convert between the solid and
liquid phases
 a gain or loss of heat
2. mol = the moles of substance (divide
given mass by molar mass)
3. ΔHfus = the molar heat of fusion (a
constant for each substance)!
Calculations of Energy Changes
C.
q = molΔHvap
 used only when the temperature is constant
1. q = the amount of heat absorbed or
released (in cal or J) for the substance
to convert between the liquid and
gas phases
 a gain or loss of heat
2. mol = the moles of substance (divide given
mass by molar mass)
3. ΔHvap = the molar heat of vaporization
(a constant for each substance)!
1
q = mc∆T
2
q = molΔHfus
3
q = mc∆T
4
q = molΔHvap
5
q = mc∆T