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.

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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 H fus ) 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 B C

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 (ΔH vap ) 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 B C 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 B C D E