1. Energy and Physical Changes – Part II
Heating Curves, Specific Heat Capacity, Molar Heat, Calculations of Physical Energy Changes

2. Heating Curves
a graph that shows the temperature vs. either time or energy
B. ENDOthermic heating curves
positive slope because heat is absorbed
shows the transformation:
solid → liquid → gas

3. Heating Curves – Endothermic
A: ↑ KE; PE constant C: ↑ KE; PE constant
B: ↑ PE; KE constant D: ↑ PE; KE constant
E: ↑ KE; PE constant

4. Heating Curves C. EXOthermic heating curves
negative slope because heat is released
shows the transformation:
gas → liquid → solid

5. Heating Curves – Exothermic
A: ↓ KE; PE constant C: ↓ KE; PE constant
B: ↓ PE; KE constant D: ↓ PE; KE constant
E: ↓ KE; PE constant

6. Specific Heat Capacity
the amount of heat necessary to convert 1 gram of a substance 1 °C
unit = cal/g x °C or J/g x °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
symbol = c
H2O has the highest specific heat capacity among any common substance

7. Molar Heat Molar Heat of Fusion
the amount of heat necessary to melt (or freeze) 1 mole of a substance at its melting point
unique to each substance
symbol = ΔHfus
only applies when there is no temperature change…describes potential energy and NOT kinetic energy

8. Molar Heat Molar Heat of Vaporization
the amount of heat necessary to evaporate (or condense) 1 mole of a substance at its boiling point
unique to each substance
symbol = ΔHvap
only applies when there is no temperature change…describes potential energy and NOT kinetic energy

9. Calculations of Energy Changes
q = mcΔT
used only for temperature changes!
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
m = the mass of substance (in grams)
ΔT = the change in temperature
Tfinal - Tinitial

10. Calculations of Energy Changes
B. q = molΔHfus
used only when the temperature is constant
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
mol = the moles of substance (divide given mass by molar mass)
ΔHfus = the molar heat of fusion (a constant for each substance)!

11. Calculations of Energy Changes
C. q = molΔHvap
used only when the temperature is constant
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
mol = the moles of substance (divide given mass by molar mass)
ΔHvap = the molar heat of vaporization (a constant for each substance)!

12. q = mc∆T
q = molΔHfus
4 q = molΔHvap
5 q = mc∆T