# Phase Changes

Phase of Matter Phases of Matter Gases indefinite volume and shape, low density. Liquids definite volume, indefinite shape, and high density. Solids definite volume and shape, high density Solids and liquids have high densities because their molecules are close together. Temperature

Measured in Celsius (C) All math is done in Kelvin (K) K = C + 273.15 55 C = _________K 350 K = _________C Standard Temp. refers to 0 C Absolute Zero 0 K lowest temp possible Kinetic Theory Kinetic theory says that molecules are in constant motion. Perfume molecules moving across the

room are evidence of this. However, not all molecules in a sample will move at the same speed Kinetic Energy and Temperature Kinetic energy is the energy of motion Temperature is a measure of the Average kinetic energy of the molecules of a substance. Higher temperature faster molecules. At absolute zero (0 K) all molecular

motion would stop. High temp. % o f M o l e c u

l e s Low temp. Kinetic Energy High temp. % o f

M o l e c u l e s Low temp. Average

kinetic energies are temperatures Kinetic Energy Temperature The average kinetic energy is directly proportional to the temperature in Kelvin If you double the temperature (in Kelvin) you double the average kinetic energy. If you change the temperature from 300 K to 600 K the kinetic energy doubles.

Heat Not the same as temperature Heat is the total kinetic energy of all particles in a substance Heat flows in or out of a substance until temperature is equalized Heat always flows from high to low temperature Heat Total kinetic energy of the molecules in a substance

Units Calorie amount of heat needed to raise the temp of 1g of water 1C Joule metric unit of heat 1 cal = 4.186 J 5.75 cal = __________J 15.5 J = __________cal Phase Changes Melting

Soli d Vaporizati on Liqui d Freezin g Gas

Condensati on Sublimation Melting Soli d Vaporizati on Liqui

d Gas Freezin Condensati g on Condensation Heat is either added or removed during phase changes For each phase change below, will heat be

absorbed or released. Describe as endothermic or exothermic. - freezing - melting - evaporating - condensing - sublimation - resublimation Entropy Disorder of particles (randomness) In nature all systems tend to disorder, increase in entropy

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