Energy Chapter 16Chapter 16

Energy: Ability to do WorkEnergy: Ability to do Work Potential Energy = Energy of Potential Energy = Energy of

positionposition AKA AKA STOREDSTORED ENERGY ENERGY

Kinetic Energy = Energy of motionKinetic Energy = Energy of motion

Radiant Energy = Electromagnetic Radiant Energy = Electromagnetic Ex: SunlightEx: Sunlight

Types of EnergyTypes of Energy

Kinetic Potential

Mechanical

Chemical Electrical Magnetic Radiant

Non-mechanical

Energy

(Not a complete list!)

Units of EnergyUnits of Energy SI system - unit of energy is the SI system - unit of energy is the

JOULEJOULE (J) (J)

1 Joule = amount of energy required 1 Joule = amount of energy required to lift a golf ball 1 meterto lift a golf ball 1 meter

Other Energy Units: Other Energy Units: calorie, Calorie, BTU’scalorie, Calorie, BTU’s

1 calorie = 4.18 Joules1 calorie = 4.18 Joules

1 Calorie = 1000 calories = 1 1 Calorie = 1000 calories = 1 kilocaloriekilocalorie

Kinetic EnergyKinetic Energy KE = ½ x Mass x VelocityKE = ½ x Mass x Velocity2 2 = ½ mV = ½ mV22

So KE depends on how heavy and how So KE depends on how heavy and how fastfast

Potential EnergyPotential Energy staplerstapler RubberbandRubberband PopperPopper

AAnythingnything can have can have PE = energy of PE = energy of position position

= stored energy= stored energy

Potential Energy can Potential Energy can be converted to be converted to Kinetic EnergyKinetic Energy

MagnetsMagnetsThe potential energy in the The potential energy in the

system of 2 magnets system of 2 magnets depends on their depends on their relativerelative positionposition

Electromagnetic RadiationElectromagnetic Radiation Sunlight – Visible radiationSunlight – Visible radiation Ultraviolet radiationUltraviolet radiation Infrared radiation Infrared radiation Gamma raysGamma rays X-raysX-rays MicrowavesMicrowaves RadiowavesRadiowaves

Applet spectrum

Energy in ChemistryEnergy in ChemistryChemical energy = energy Chemical energy = energy

stored in bondsstored in bonds

HeatHeat – form of energy that – form of energy that flows flows from warmer object to cooler from warmer object to cooler objectobject (Macroscopic)(Macroscopic)

Heat EnergyHeat EnergyHeat: energy associated with Heat: energy associated with

the motion of atoms & the motion of atoms & molecules in mattermolecules in matter(Microscopic)(Microscopic)

Symbol for heat energy = Symbol for heat energy = Q or qQ or q

Heat EnergyHeat EnergyHeat depends on amount Heat depends on amount

of substance presentof substance present

We measure heat We measure heat changeschanges

TemperatureTemperature = measure of average kinetic = measure of average kinetic

energy of energy of particles of substanceparticles of substance

Swimming Pool vs. MugSwimming Pool vs. Mug

Temperature is Temperature is NOTNOT energy energy Temperature does NOT depend on Temperature does NOT depend on

amount of substance; energy doesamount of substance; energy does

Law of Conservation of Law of Conservation of EnergyEnergy

Energy is Energy is neither created nor neither created nor destroyeddestroyed in ordinary chemical or in ordinary chemical or physical changephysical changeEnergy before = Energy afterEnergy before = Energy after

Energy Energy cancan be converted be converted from one from one formform to anotherto another

- potential to kinetic- potential to kinetic - radiant to electric- radiant to electric- electric to heat- electric to heat - chemical to kinetic- chemical to kinetic- chemical to electrical- chemical to electrical

All physical & chemical All physical & chemical changes are accompanied changes are accompanied

by change in energyby change in energy

The chemistry ofThe chemistry of energy energy changes changes is known asis known as Thermochemistry!Thermochemistry!

Energy TransferEnergy Transfer Measure Measure changeschanges in heat in heat

amount of energy transferred from one amount of energy transferred from one substance to anothersubstance to another

You can You can measuremeasure energy lostenergy lost somewhere somewhere oror the the energy gainedenergy gained somewhere elsesomewhere else

CannotCannot measure absolute heatmeasure absolute heat content content of systemof system

Energy of Universe is conserved

Universe

EnvironmentEnvironment

System

Energy

Energy can move between the system and the environment

ExothermicExothermic Change Change System System releases heat releases heat toto environment environment

What happens to the temperature of the What happens to the temperature of the environment?environment?

EXO - energy leaves system (EXO - energy leaves system (exitsexits))

What happens to the energy level of What happens to the energy level of the system?the system? What happens to temperature of What happens to temperature of

system?system?

Environment

System

Energy

EXEXO - energy leaves O - energy leaves system (system (exexits)its)

Temperature of Temperature of environment environment

Temperature of Temperature of system system

ExothermicExothermic Change ChangeSystemSystem has has net energy lossnet energy loss!!EnvironmentEnvironment has has net energy net energy

gaingain!!

Energy lost = Energy gainedEnergy lost = Energy gained

EndothermicEndothermic Change Change System System absorbs heat absorbs heat fromfrom environment environment

What happens to temperature of What happens to temperature of environment?environment?

Endo - Energy Endo - Energy entersenters system system

What happens to the energy level of What happens to the energy level of the system?the system? What happens to temperature of system?What happens to temperature of system?

Endo - Energy Endo - Energy ententers system ers system ((ententrance)rance)

Environment

System

Energy

Temperature of Temperature of environment environment

Temperature of Temperature of system system

EndothermicEndothermic Change ChangeSystemSystem has has net energy gainnet energy gain!!EnvironmentEnvironment has has net energy net energy

lossloss!!

Energy lost = Energy gainedEnergy lost = Energy gained

Heat FlowHeat FlowHeat flows from hotter object Heat flows from hotter object

to cooler objectto cooler object

Cold pack on leg: Heat flows Cold pack on leg: Heat flows from the leg to the cold pack!from the leg to the cold pack! Leg cools down; cold pack warms Leg cools down; cold pack warms

upup

Quantity of heat transferredQuantity of heat transferredQuantity (amount) of heat Quantity (amount) of heat

transferred depends on transferred depends on Temperature changeTemperature change Mass of substanceMass of substance Specific Heat of substanceSpecific Heat of substance

Calculating Heat TransferredCalculating Heat Transferred

Q = mCQ = mCTT

Simple system: •pure substance in a single phase •calculate heat gained or lost using:

Q = amount of heat transferredQ = amount of heat transferredm = mass of substancem = mass of substanceC = specific heat capacity of the substance.C = specific heat capacity of the substance.T = temperature change = TT = temperature change = Tfinalfinal – T – Tinitialinitial

Specific HeatSpecific Heat Amount heat energy required to Amount heat energy required to raise temp of 1 gram of substance by raise temp of 1 gram of substance by

11ooCC

Symbol = cSymbol = c

Specific heat = a Specific heat = a physical constantphysical constant Different for each pure substanceDifferent for each pure substance

Calorimeter

source

Another example

CalorimetryCalorimetry Changes in heat energy are measured by Changes in heat energy are measured by

calorimetrycalorimetry ““universe” is contained in styrofoam cupuniverse” is contained in styrofoam cup

““enviroment” is water****enviroment” is water****

““system” is whatever we put in the watersystem” is whatever we put in the water

CalorimetryCalorimetry Energy lost = Energy gainedEnergy lost = Energy gained

Difficult to monitor “system”Difficult to monitor “system” Easy to monitor “environment” (water)Easy to monitor “environment” (water)

Energy lost/gained by environment = Energy lost/gained by environment = Energy gained/lost by systemEnergy gained/lost by system

CalorimetryCalorimetry10 grams of NaOH is dissolved in 100 g of 10 grams of NaOH is dissolved in 100 g of

water & the temperature of the water water & the temperature of the water increases from 22increases from 22C to 30C to 30CC

was dissolving process endothermic or was dissolving process endothermic or exothermic exothermic

how do you know?how do you know?

Exothermic – temperature of Exothermic – temperature of environment environment ↑↑

DissolvingDissolving What’s happening when NaOH dissolves?What’s happening when NaOH dissolves?

Add HAdd H22OO

molecules close together, molecules close together, not interactingnot interacting

molecules pulled apart & molecules pulled apart & interacting with Hinteracting with H22OO

CalorimetryCalorimetry Calculate energy released by NaOH as it Calculate energy released by NaOH as it

dissolved in waterdissolved in waterEnergy lost by NaOH = Energy gained by Energy lost by NaOH = Energy gained by

water Easier to calculate from Hwater Easier to calculate from H22O O perspectiveperspective

Q = mCQ = mCTTQ = energy (joules)Q = energy (joules)M = mass (grams)M = mass (grams)C = specific heat capacity (Table B)C = specific heat capacity (Table B)T = temperature change = TT = temperature change = Tff - T - Tii

Calorimetry & Q = mCCalorimetry & Q = mCTT temperature of water increased from temperature of water increased from

2222C to 30C to 30CC 3030C -22C -22C = C = 88C = C = TT

What mass to use? Well, temp What mass to use? Well, temp change was for water, so want mass change was for water, so want mass of water of water m = 100 gm = 100 g

Same goes for specific heat capacity; Same goes for specific heat capacity; calculate heat absorbed by water calculate heat absorbed by water

ccHH220 0 = 4.18J/g= 4.18J/g

Q = mCQ = mCTTQ = (100 g)(4.18 J/gQ = (100 g)(4.18 J/g(8(8C)C)

Q = 3344 JoulesQ = 3344 Joules

Stability and EnergyStability and Energy If If energy is high, stability is lowenergy is high, stability is low

If If energy is low, stability is highenergy is low, stability is high