DALTON'S LAW OF PARTIAL PRESSURES

• According to Dalton's law, the total pressure exerted by a mixture of gases is equal to the sum of the partial pressures of the gases in the mixture.

Zn(s) + NH4NO3(s) → N2(g) + 2 H2O(g)  + ZnO(s)

gases individualtotal PP

PARTIAL PRESSURE• The partial pressure of an individual gas of a mixture is the

pressure the gas would exert if it were alone in the container at the same temperature as the mixture as shown in the following illustration:

GRAHAM'S LAW• Graham's law is a mathematical

expression that relates the rates of effusion or diffusion of two gases to the masses of the molecules of the two gases.

• EFFUSION• Effusion is a process in which a gas

escapes from a container through a small hole in the container.

• DIFFUSION• Diffusion is a process that causes

gases to spontaneously mix when they are brought together.

MATHEMATICAL EXPRESSION OF GRAHAM'S LAW

Aof mass molecular

B of mass molecular

B of rate effusion

Aof rate effusion

GRAHAM'S LAW CALCULATION EXAMPLE

• Compare the rates of effusion or diffusion for neon and krypton gases.

• Solution: The molecular masses of neon and krypton are 20.18 u and 83.80 u, respectively. These are the molecular weights of the gases from the periodic table. Substitution into the Graham's law equation gives the following:

Thus, the rate of Ne = (2.038) rate of Kr. Stated another way, neon gas effuses or diffuses about twice as fast as krypton gas.

038.2153.4u 20.18

u 83.80

Kr rate

Ne rate

CHANGES IN STATE• Changes in state are often accomplished by adding or removing

heat from a substance.• Changes in state caused by adding heat to a substance are

classified as endothermic (heat in) processes. • Changes in state caused by removing heat are classified as

exothermic (heat out) processes.

ENDOTHERMIC PROCESSES• EVAPORATION OR

VAPORIZATION• Evaporation or vaporization is an

endothermic process in which a liquid is changed to a gas.

• SUBLIMATION• Sublimation is an endothermic

process in which a solid is changed to a gas without first melting to a liquid.

• MELTING OR FUSION• Melting or fusion is an endothermic

process in which a solid is changed to a liquid.

EXOTHERMIC PROCESSES• LIQUEFACTION OR CONDENSATION

• Liquefaction or condensation is an exothermic process in which a gas is changed to a liquid.

• DEPOSITION OR CONDENSATION• Deposition or condensation is an

exothermic process in which a gas is changed into a solid.

• FREEZING OR CRYSTALLIZATION• Freezing or crystallization is an

exothermic process in which a liquid is changed into a solid.

VAPOR PRESSURE• Vapor pressure is the pressure exerted by a vapor that is in

equilibrium with its liquid.

BOILING POINT• The boiling point of a liquid is the temperature at which the

vapor pressure of the liquid is equal to the prevailing atmospheric pressure.

• The normal or standard boiling point is the temperature at which the vapor pressure of a liquid is equal to 1 standard atmosphere (760 torr).

VARIATION OF WATER BOILING POINT WITH ELEVATION

SUBLIMATION AND MELTING• Sublimation is the endothermic process in which a solid is

changed directly to a gas without first becoming a liquid.

ENERGY AND THE STATES OF MATTER

• At 760 torr, constant heat is applied until a 1 g sample of ice at -20°C is converted to steam at 120°C.

• This is a five step process: (AB) heating ice to melting point, (BC) melting ice, (CD) heating liquid to boiling point, (DE) boiling water, and (EF) heating steam.

SPECIFIC HEAT• The specific heat of a substance is the amount of heat required

to raise the temperature of exactly 1 g of a substance exactly 1°C.

HEATS OF FUSION & VAPORIZATION

• HEAT OF FUSION• The heat of fusion of a substance is the amount of heat

required to melt exactly 1g of a solid substance at constant temperature.

• HEAT OF VAPORIZATION• The heat of vaporization of a substance is the amount of

heat required to vaporize exactly 1g of a liquid substance at constant temperature.