Unit Five - Heat of Vaporization & Heat of Fusion & Chemical Properties

Ex: The heat of vaporization of water is 2.3 x 103 J/g at 101.3kPa pressure and 100oC. How much heat must be supplied to evaporate 50.g of water at 100oC and 101.3kPa.

50g X (2.3 x 10^3 J/g) 1.2 x 10^5 J 120000 J

Ex: The heat of fusion of ice at 0o C is 3.4 x 102 J/g. How much heat is needed to change 75g of ice at 0o C to liquid water at the same temperature?

75g x (3.4 x 10^2 J/g) = 2.6 x 10^4 J

Chemical Change

A new substance is formed with new, distinctive properties

Ex. of Chemical Change

Color, light, precipitate, heat, gas

Ex. of Chemical Property

Corrosiveness, flammability, combustibility, reaction to acid

Chemical Property

How the substance "behaves" or interacts with other chemicals

Heat of Vaporization

The quantity of energy needed to vaporize a unit mass of a liquid at constant temperature

Heat of Fusion

The quantity of heat needed to change a unit mass of solid to a liquid at a constant temperature

What is the formula for heat fusion?

q = m x △HFusion Heat to fuse (melt) a substance = Mass of the substance x Heat of Fusion of the substance

What is the formula for heat vaporization?

q = m x △HVaporization Heat to vaporize a substance = Mass of the substance x Heat of vaporization of the substance