DALTON'S LAW OF PARTIAL PRESSURES

1. 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)

2. 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:

3. GRAHAM'S LAW • Graham's law is a mathematical expression that relates the rates of effusionor diffusionof 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.

4. MATHEMATICAL EXPRESSION OF GRAHAM'S LAW

5. GRAHAM'S LAWCALCULATION 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.

6. 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.

7. 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.

8. EXOTHERMIC PROCESSES • LIQUEFACTION ORCONDENSATION • Liquefaction or condensation is an exothermic process in which a gas is changed to a liquid. • DEPOSITION ORCONDENSATION • 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.

9. VAPOR PRESSURE • Vapor pressure is the pressure exerted by a vapor that is in equilibrium with its liquid.

10. 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 standardboiling point is the temperature at which the vapor pressure of a liquid is equal to 1 standard atmosphere (760 torr).

11. VARIATION OF WATER BOILING POINT WITH ELEVATION

12. SUBLIMATIONAND MELTING • Sublimation is the endothermic process in which a solid is changed directly to a gas without first becoming a liquid.

13. 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.

14. 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.

15. 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.