Thermo Notes #4: States of Matter and Phase Changes WCHS Chemistry

Phase Change Thinker When you place a beaker full of water over a lit Bunsen Burner, why does the temperature increase? H2O molecules gain energy from the exothermic reaction at the bunsen burner. This increases the kinetic energy of the particles. Temp = a measurement of the average KE of the particles, so temp increases Why does the temperature of the water stop increasing when the water boils? Once the temper of the H2O = 100C, it’s reached its BP At this point all of the added energy is going towards the particles becoming a gas (changing phase) NONE of the energy is going toward raising the temperature!!!!

Particles are in fixed positions Solids Particles are in fixed positions Close together Vibrate in place Definite shape and volume **Not a lot of Kinetic Energy**

Liquids Particles can slide past one another. Move fast enough to overcome forces of attraction. Can change shape, but NOT volume **Move around → have some KE**

Gases Particles move rapidly Do not feel forces of attraction. Expand to fill all available space. Can change shape AND volume **Rapid movement → have LOTS of kinetic energy!**

During a phase change, there is NO change in temperature (= flat lines on graph) Phase Changes = the conversion of a substance from one physical form to another. Sublimation Deposition Melting Vaporization Freezing Condensation

Heating & Cooling Curve of Water Exothermic Releases cooling warming Condensation cooling vaporization freezing Endothermic warming cooling Melting Absorbs warming