Kinetic Energy and Changes of State Section 10.2

Temperature Temperature- according to the kinetic theory, the measure of the average kinetic energy of the particles in the material. Kinetic energy is dependent on mass and speed. Kinetic energy = ½ mv2 Diffusion- the process by which particles of a gas fill a space because of random motion.

Kelvin Scale Kelvin scale- the SI unit of temperature Absolute zero- the temperature at which a substance would have no kinetic energy. At absolute zero, no particles would be moving. Speed and kinetic energy would both be zero.   The temperature of a substance is directly proportional to the average kinetic energy of the particles. Zero on the Kelvin scale corresponds to zero kinetic energy.

One Kelvin = one degree Celsius 0 K= -273oC = -460oF 273 K = 0oC = 32oF 373 K = 100oC = 212oF  

Conversions TK = ( TC + 273) K TC = (TK – 273) oC Converting 25oC to Kelvin: TK = ( 25 + 273) K TK= 298K   Converting 345K to Celsius: TC = (345 – 273) oC TC = 72 oC

Gas- liquid- solid

Liquid Gas   Evaporation- the process by which particles of a liquid form a gas by escaping from the surface. It is affected by surface area, temperature and humidity. There is a minimum amount of kinetic energy required to escape the liquid and become a gas.

Liquid Gas Vapor Vapor- the gaseous state of a substance that is normally a liquid at room temperature Vapor pressure- the pressure of a gaseous substance in equilibrium with its liquid.  The value of the vapor pressure indicates how easily the substance evaporates or how volatile it is. Vapor pressure is affected by molecular weight and intermolecular forces.

Liquid Gas Boiling Boiling point- the temperature of the substance when its vapor pressure equals the pressure exerted on the surface of the liquid. Boiling point increases with an increase in pressure and decreases with a decrease in pressure.

Heat of vaporization- the energy absorbed when 1 g of a liquid vaporizes at its normal boiling point. Hv = 2260 J/kg for water When a liquid boils, heat is transferred from the surroundings to the liquid/gas.

Gas liquid Condensation- the process by which the particles of a gas come closer together until they form a liquid (the opposite of evaporation). When a gas condenses, heat is transferred from the gas to the surroundings.

Solid Liquid Melting point- the temperature of a solid when its crystal lattice begins to disintegrate. Freezing point- the temperature of a liquid when it begins to form a crystal lattice and becomes a solid. Heat of fusion- the energy released as 1 g of a substance solidifies at its freezing point Hf = 334 J/g for water When a liquid freezes, heat is transferred from the liquid to the surroundings.

Solid ---- gas Sublimation- the process by which particles of a solid escape from its surface and become a gas (without melting). When a solid sublimes, heat is transferred from the surroundings to the solid/gas.