Heating and Cooling Curve Definitions:• Specific Heat: Amount of energy required to raise the

temperature of 1 gram of a substance by 1⁰ Celsius • Enthalpy of Fusion/Molar Heat of Fusion: Energy

required to change 1 gram of a substance from solid to liquid OR energy released when changing from liquid to solid

• Enthalpy of Vaporization/Molar Heat of Vaporization: Energy required to change 1 gram of a substance from liquid to gas OR energy released when changing from gas to liquid

The graph below shows the relationship between heat (energy) added, in calories (cal), and temperature for 1 g of water. A

student applied heat to 1 g of ice that had been cooled to -40⁰C and measured the rise in temperature.

Step A: Solid Water (Ice) Rises in Temperature

• If the temperature is not at 0°C, it will rise as heat is added to get there. (Kinetic energy is increasing)

• Each gram of water requires a constant amount of energy to increase 1°C = SPECIFIC HEAT!

• Important – The ice has not melted yet!

A

Step B: Solid Water (Ice) Melts

• By adding energy the ice begins to melt• Temperature does not increase as more energy is

being added (Kinetic energy is staying constant, but potential energy is increasing)

• Each mole of water requires a given amount of energy to melt = Molar Heat of Fusion (Δ Hfus) in kJ/mole.

• Energy is overcoming water molecules attraction for each other so it can be converted from a solid to liquid

A

B

Step C: Liquid Water Rises in Temperature

• Now the ice is completely melted and the water temperature begins to rise as heat is added. (specific heat)

• Kinetic Energy is increasing• The water has not started to boil yet.

A

BC

Step D: Liquid Water Boils

• As we add energy the temperature does not change.

• Each mole of water will require a constant amount of energy to boil = Molar Heat of Vaporization (ΔHvap) kJ/mole.

• The energy is being used to overcome water’s attraction to each other to convert the liquid to a gas. (Kinetic energy is remaining constant but potential energy is increasing)

A

BC

D

Step E: Steam Rises in Temperature

• Temperature rises again when all water is turned to steam

• Each gram of water requires a constant amount of energy to rise 1° = specific heat!

A

BC

DE