Chapter 9 and 10Thermal Energy                                                <>

ReviewReview• Thermal or internal energy in a substance is the Thermal or internal energy in a substance is the

total energy of all its atoms and molecules.total energy of all its atoms and molecules.• Temperature is the average kinetic energy per Temperature is the average kinetic energy per

molecule in a substance (high temperature means molecule in a substance (high temperature means high kinetic energy of atoms/molecules)high kinetic energy of atoms/molecules)

• No upper limit of temperature but absolute zero (0 No upper limit of temperature but absolute zero (0 K and -273K and -273°°C) is lowest temperatureC) is lowest temperature

• Heat (measured in Joules) is the transfer of Heat (measured in Joules) is the transfer of thermal energy from one substance to another thermal energy from one substance to another due to a temperature difference between the two due to a temperature difference between the two substances.substances.

Laws of Thermodynamics• 11stst Law: Whenever heat flows into or Law: Whenever heat flows into or

out of a system, the gain or loss of out of a system, the gain or loss of thermal energy equals the amount of thermal energy equals the amount of heat transferred.heat transferred.

• 22ndnd Law: Heat never spontaneously Law: Heat never spontaneously flows from a cold substance to a hot flows from a cold substance to a hot substance.substance.

• 33rdrd Law: No system can reach absolute Law: No system can reach absolute zero.zero.

Thermal Expansion• Molecules in a hot substance move faster Molecules in a hot substance move faster

and therefore, move further apart. and therefore, move further apart. (class demo)(class demo)– Objects expand when heated and contract Objects expand when heated and contract

when cooled. (ball and ring demo)when cooled. (ball and ring demo)– Must be taken into account when making Must be taken into account when making

things with various substances because things with various substances because objects have different rates of thermal objects have different rates of thermal expansion.expansion.

Heat Transfer• Three types~Three types~

– Conduction: heat transfer by particle collisionsConduction: 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 Convection: heat transfer by movements of fluid or currentscurrents

• 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 energyRadiation: heat transfer by radiant energy• In the form of electromagnetic waves from radio to gamma In the form of electromagnetic waves from radio to gamma • All substances above absolute zero emit radiant energy and All substances above absolute zero emit radiant energy and

absorb energy absorb energy

Heat Transfer Causes Phase Changes

• Matter exists in four phases:Matter exists in four phases:– Solid, liquid, gas, and plasmaSolid, liquid, gas, and plasma

• When thermal energy is added to each phase, When thermal energy is added to each phase, the increased motion breaks down the rigid the increased motion breaks down the rigid molecular structure and causes it to change molecular structure and causes it to change phase. phase. (Examples…)(Examples…)

• When thermal energy is taken away, motion When thermal energy is taken away, motion slows between molecules until attractive forces slows between molecules until attractive forces between them bind them together. between them bind them together. (Examples…)(Examples…)

Melting Ice ExplorationPurpose Question:Purpose Question:What is the affect of adding thermal energy to What is the affect of adding thermal energy to

the temperature and phase of a beaker of the temperature and phase of a beaker of ice? ice?

Hypothesis:Hypothesis:Variables:Variables:

manipulated-manipulated-responding-responding-controlled-controlled-experimental control-experimental control-

Procedure:Procedure:• Fill a beaker full of iceFill a beaker full of ice• Take initial temperature of ice using a Take initial temperature of ice using a

thermometer.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 Take temperature of beaker every two

minutes and record temperature and phase(s) minutes and record temperature and phase(s) of water in table.of water in table.

• Turn heat up a little every ten minutes until it is Turn heat up a little every ten minutes until it is all the way up.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 Energy gained when changing from a solid to a liquid or lost when changing from a liquid to a liquid or lost when changing from a liquid to a solid (a solid (ΔΔQ= 335 J/g for water)Q= 335 J/g for water)

• Enthalpy of vaporizationEnthalpy of vaporization– Energy gained when changing from a liquid to Energy gained when changing from a liquid to

a gas or lost when changing from a gas to a a gas or lost when changing from a gas to a liquid (liquid (ΔΔQ= 2255 J/g for water)Q= 2255 J/g for water)

– Stage that requires the most energyStage that requires the most energy