Gas Densities, Partial Pressures, and Kinetic-Molecular Theory Sections 10.5-10.8.
DALTON'S LAW OF PARTIAL PRESSURES According to Dalton's law, the total pressure exerted by a mixture...
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Transcript of DALTON'S LAW OF PARTIAL PRESSURES According to Dalton's law, the total pressure exerted by a mixture...
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.