Chapter 9 and 10 Thermal Energy <>

Review Thermal or internal energy in a substance is the total energy of all its atoms and molecules.Thermal or internal energy in a substance is the total energy of all its atoms and molecules. Temperature is the average kinetic energy per molecule in a substance (high temperature means high kinetic energy of atoms/molecules)Temperature is the average kinetic energy per molecule in a substance (high temperature means high kinetic energy of atoms/molecules) No upper limit of temperature but absolute zero (0 K and -273°C) is lowest temperatureNo upper limit of temperature but absolute zero (0 K and -273°C) is lowest temperature Heat (measured in Joules) is the transfer of thermal energy from one substance to another due to a temperature difference between the two substances.Heat (measured in Joules) is the transfer of thermal energy from one substance to another due to a temperature difference between the two substances.

Laws of Thermodynamics 1 st Law: Whenever heat flows into or out of a system, the gain or loss of thermal energy equals the amount of heat transferred.1 st Law: Whenever heat flows into or out of a system, the gain or loss of thermal energy equals the amount of heat transferred. 2 nd Law: Heat never spontaneously flows from a cold substance to a hot substance.2 nd Law: Heat never spontaneously flows from a cold substance to a hot substance. 3 rd Law: No system can reach absolute zero.3 rd Law: No system can reach absolute zero.

Thermal Expansion Molecules in a hot substance move faster and therefore, move further apart. (class demo)Molecules in a hot substance move faster and therefore, move further apart. (class demo) –Objects expand when heated and contract when cooled. (ball and ring demo) –Must be taken into account when making things with various substances because objects have different rates of thermal expansion.

Heat Transfer Three types~Three types~ –Conduction: heat transfer by particle collisions Mainly in solids because particles are close togetherMainly in solids because particles are close together Brainstorm conductors and insulatorsBrainstorm conductors and insulators –Convection: heat transfer by movements of fluid or currents Mainly in gases and liquids because particles flowMainly in gases and liquids because particles flow Expanding and condensing liquids and gases.Expanding and condensing liquids and gases. Brainstorm examples.Brainstorm examples. –Radiation: heat transfer by radiant energy In the form of electromagnetic waves from radio to gammaIn the form of electromagnetic waves from radio to gamma All substances above absolute zero emit radiant energy and absorb energyAll substances above absolute zero emit radiant energy and absorb energy

Heat Transfer Causes Phase Changes Matter exists in four phases:Matter exists in four phases: –Solid, liquid, gas, and plasma When thermal energy is added to each phase, the increased motion breaks down the rigid molecular structure and causes it to change phase.When thermal energy is added to each phase, the increased motion breaks down the rigid molecular structure and causes it to change phase.(Examples…) When thermal energy is taken away, motion slows between molecules until attractive forces between them bind them together.When thermal energy is taken away, motion slows between molecules until attractive forces between them bind them together.(Examples…)

Melting Ice Exploration Purpose Question: What is the affect of adding thermal energy to the temperature and phase of a beaker of ice? Hypothesis:Variables:manipulated-responding-controlled- experimental control-

Procedure: Fill a beaker full of iceFill a beaker full of ice Take initial temperature of ice using a thermometer.Take initial temperature of ice using a thermometer. Put beaker on hot plate that is turned on low.Put beaker on hot plate that is turned on low. Take temperature of beaker every two minutes and record temperature and phase(s) of water in table.Take temperature of beaker every two minutes and record temperature and phase(s) of water in table. Turn heat up a little every ten minutes until it is all the way up.Turn heat up a little every ten minutes until it is all the way up. Continue collecting data for 45 minutes.Continue collecting data for 45 minutes. Graph data.Graph data.

Phase Change Graph

Heat needed to change phases Enthalpy of fusionEnthalpy of fusion –Energy gained when changing from a solid to a liquid or lost when changing from a liquid to a solid (ΔQ= 335 J/g for water) Enthalpy of vaporizationEnthalpy of vaporization –Energy gained when changing from a liquid to a gas or lost when changing from a gas to a liquid (ΔQ= 2255 J/g for water) –Stage that requires the most energy