Heat, Temperature & Specific Heat

Thermal Energy Total energy in molecules of a substance including a) kinetic E of moving molecules b) potential E stored in chemical bonds

Temperature = Average kinetic energy per molecule Average speed of molecule KE = ½ m V2 m = mass V = velocity Velocity or speed is most important 0 velocity = absolute 0….no motion of particles

Heat = Flow of thermal Energy from hot to cold Energy of internal motion of molecules as it transfers from 1 object to another Transfer of kinetic energy from one molecule to another http://www.gcse.com/energy/images/conduction.gif

Laws of Thermodynamics 1) Energy can not be created or destroyed only converted from one form to another or transferred from one place to another 2) Heat energy flows from high temperature areas to low temperature areas only

Thermal equilibrium No net flow of heat energy because all areas are the same temperature Heat flows from hot to cold until…. Thermal equilibrium is reached…. Then it just passes back and forth Still moving so still heat!

Thermometers… Measure their own temperature Put thermometer in water. Heat flows Molecules of alcohol speed up and expand or slow down and contract Thermal equilibrium between thermometer and water causes red line to stop moving. http://www.middleschoolchemistry.com/multimedia/chapter1/lesson3#heating_and_cooling_a_thermometer

Measurments & Units Temperature is measured in… o Celsius Heat is measures in…. calories 1 calorie = the amount of heat needed to raise the temp of 1ml H2O by 1 o C

The Calories in your food are Calories, They are actually Kilocalories = the amount of heat needed to warm up 1,000 ml of H2O by 1 oC

Specific Heat It takes more heat energy to increase the temperature of some substances. We say those substances have a high specific heat. Water has very High specific heat Specific heat is measured in cal/ml/oC or cal/g/oC

Specific Heat High specific heat warms up slower AND Cools off slower http://oceanservice.noaa.gov/education/pd/oceans_weather_climate/media/specific_heat.swf More massive http://mw2.concord.org/public/part2/heat/page2.cml

Heat is Transferred in 3 ways 1) Conduction – objects touch, direct heat transfer from warm object to cold object 2) Convection – heat transferred by flowing molecules 3) Radiation – electromagnetic waves = Infrared light waves heat waves, not visible

1) Conduction Metals are good conductors because their electrons are loosely held (can flow) Non-metals hold their electrons tightly so are poor conductors called… insulators

2) Convection warm , fast moving molecules rise carrying heat with them (they expand & become less dense)

3) Radiation Electromagnetic waves =light waves Not visible Heat waves

http://www.bbc.co.uk/schools/ks3bitesize/science/energy_electricity_forces/energy_transfer_storage/activity.shtml

Heat transfer causes phase change Lowest energy = solid a) strongest intermolecular forces b) molecules vibrate in place so definite shape and volume Medium energy = Liquid a) weaker intermolecular forces allow molecules to flow around each other so no definite shape b) still to low energy for molecules to break away completely and expand so definite volume

Highest energy = gas a) weakest intermolecular forces b) molecules can flow & expand c) no definite shape or volume

Phase changes : Change in amount of thermal energy cause molecules to move in different ways Higher energy = weaker intermolecular forces as molecules expand Mass does not change Density changes

Phase Change Diagram to be in that phase Solid Liquid Gas low high x = Heat energy (per mole) needed to be in that phase

Phase Change Diagram: Water

Warming A-B Warming ice Add E, Temp B-C Melting Add E, no ∆ Temp E used to break intermolecular forces so molecules can flow

Warming C-D Warming water Add E, Temp D-E vaporization Add E, no ∆ Temp E used to break intermolecular forces so molecules can expand

Vaporization changes liquid to gas Boiling Bubbles of gas form at bottom of liquid Evaporation High energy molecules break loose from surface of fluid

Cooling F-E Cooling steam Remove E, Temp E – D condensing Remove E, no ∆ Temp Loss of E lets intermolecular forces reform & hold molecules together

Cooling D-C Cooling water Remove E, Temp C-B freezing Remove E, no ∆ Temp Loss of E strengthens intermolecular forces so molecules can only vibrate