EnergyEnergy

Chapter 16Chapter 16

Energy: Ability to do WorkEnergy: Ability to do Work

Potential Energy (PE) = Energy of positionPotential Energy (PE) = Energy of position aka aka STOREDSTORED energy energy

Kinetic Energy (KE) = Energy of motionKinetic Energy (KE) = Energy of motion

Radiant Energy = Electromagnetic Radiant Energy = Electromagnetic radiationradiation

ex: sunlightex: sunlight

Some Types of EnergySome Types 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 SI system - unit of energy is JOULEJOULE (J) (J)

1 Joule 1 Joule ≅≅ amount of energy required to amount of energy required to

lift 1 golf ball about 1 meterlift 1 golf ball about 1 meter

other energy units: other energy units: calorie (cal) calorie (cal) Calorie (Cal)Calorie (Cal) british thermal units (BTU)british thermal units (BTU)

1 calorie = 4.18 Joules1 calorie = 4.18 Joules

1 Calorie = 1000 cal = 1 kilocalorie = 1 Calorie = 1000 cal = 1 kilocalorie = 4180J4180J

Kinetic EnergyKinetic Energy

KE = ½ x mass x velocityKE = ½ x mass x velocity2 2 = ½ mv = ½ mv22

so KE of matter depends on:so KE of matter depends on:

how heavy how heavy and and how fast how fast

Potential EnergyPotential Energy

staplerstapler rubberbandrubberband popperpopper

anything can have anything can have PE PE

= energy of position = energy of position

= stored energy= stored energy

PE can be PE can be

converted to KEconverted to KE

MagnetsMagnets

PE in the system of 2 PE in the system of 2 magnets depends on their magnets depends on their relativerelative positionposition when magnets get close together they when magnets get close together they

will pull together due to attractionwill pull together due to attraction when magnets are far apart they can’t when magnets are far apart they can’t

attract each other attract each other

Electromagnetic RadiationElectromagnetic Radiation sunlight – visible sunlight – visible

radiationradiation ultraviolet radiationultraviolet radiation infrared radiation infrared radiation gamma raysgamma rays

x-raysx-rays microwavesmicrowaves radiowavesradiowaves

Energy in ChemistryEnergy in Chemistry

chemical energy: chemical energy: energy stored within energy stored within chemical bonds between atomschemical bonds between atoms

heatheat: : form of energy form of energy flows from warmer object to flows from warmer object to

cooler objectcooler object

Heat EnergyHeat Energy

heat: energy associated with heat: energy associated with motion motion

of atoms/molecules in of atoms/molecules in mattermatter

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

Heat EnergyHeat Energy

heat depends on amount heat depends on amount of substance presentof substance present

can only measure can only measure changeschanges in in heat energyheat energy not absolute value of heat not absolute value of heat

energyenergy

TemperatureTemperaturemeasure of average KE of particles in submeasure of average KE of particles in sub

temperature is temperature is NOTNOT energy energy TEMP does NOT depend on amount TEMP does NOT depend on amount

ENERGY does !ENERGY does !

Law of Conservation of Law of Conservation of EnergyEnergy

energy is energy is neither created nor destroyedneither created nor destroyed in in ordinaryordinary chemical or physical change chemical or physical change

reminder: nuclear rxn a reminder: nuclear rxn a smallsmall amount of amount of mass is converted to energymass is converted to energy

energy before = energy afterenergy before = energy after

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

potential to kineticpotential to kinetic

radiant to electricradiant to electric

electric to heatelectric to heat

chemical to kineticchemical to kinetic

chemical to electricalchemical to electrical

golf ball hit off tee

solar heat to electricity

electric stove cooking food

burning charcoal on grill

batteries creating electricity

ALL physical & chemical ALL physical & chemical changes are accompanied changes are accompanied

by change in energyby change in energy

Thermochemistry:Thermochemistry:

chemistry ofchemistry of energy changes energy changes

Energy TransferEnergy Transfer

measure measure changeschanges in heat ( in heat (amount amount energy transferred from one substance energy transferred from one substance to another)to another)

measuremeasure energy lostenergy lost somewhere somewhere

oror

energy gainedenergy gained somewhere else somewhere else

energy of universe is conserved

universe (room)

Environmentenvironment (container)

system (substances)

energy

energy can move between system and environment (goes in or out)

EXothermicEXothermic Change Change system system releases heat releases heat toto environment environment

what happens to temperature of what happens to temperature of environmentenvironment??

EXo - heat is EXitingEXo - heat is EXiting

what happens to temperature of what happens to temperature of systemsystem??

environment

system

temperature of system temperature of system

temperature of environment

what happens to energy level of system? ↓

ExothermicExothermic Change Change

energy lost = energy gainedenergy lost = energy gained

(system) (environment)(system) (environment)

EndothermicEndothermic Change Change system system absorbs heat absorbs heat fromfrom environment environment

what happens to temperature of what happens to temperature of environmentenvironment??

ENdo - heat ENdo - heat ENtersENters system system

what happens to temperature of what happens to temperature of systemsystem??

environment

system

temperature of environment temperature of environment

temperature of system temperature of system

what happens to energy level of system? ↑

EndothermicEndothermic Change Change

energy lost = energy energy lost = energy gainedgained

(environment) (system)(environment) (system)

Heat FlowHeat Flow

heat ALWAYS flows from heat ALWAYS flows from hotter object to cooler objecthotter object to cooler object

cold pack on leg: cold pack on leg: heat flows from leg to cold heat flows from leg to cold

pack!pack!• leg cools down; cold pack warms upleg cools down; cold pack warms up

CalorimetryCalorimetry

changes in heat energy are measured changes in heat energy are measured using calorimeter using calorimeter (energy lost = energy (energy lost = energy gained)gained)

difficult to monitor difficult to monitor ““systemsystem”” easy to monitor easy to monitor ““environmentenvironment”” (water) (water)

energy lost/gained by environment = energy lost/gained by environment =

energy gained/lost by systemenergy gained/lost by system

calorimeter:used to measure heat changes

“universe” = styrofoam cup

“enviroment” = water****

“system” is whatever put in water (reactants)

quantity (amount) of heat quantity (amount) of heat transferred depends on:transferred depends on:

amount temperature changeamount temperature 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 single phase •calculate heat gained or lost using:

Q = amount of heat transferredQ = amount of heat transferred

m = mass of substancem = mass of substance

c = specific heat capacity of the substancec = 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 unique for each pure substanceunique for each pure substance see Table B for water (4.18J/g˚C)see Table B for water (4.18J/g˚C)

typical word problemtypical word problem

10 grams of NaOH(s) is dissolved in 100 g 10 grams of NaOH(s) is dissolved in 100 g of water & the temperature of the water of water & the temperature of the water increases from 22increases from 22C to 30C to 30C.C.

dissolving process:dissolving process: was it endothermic or exothermic? was it endothermic or exothermic? how do you know?how do you know?

temperature temperature ↑↑

exothermicexothermic

Solid Dissolving in WaterSolid Dissolving in Water

WhatWhat’’s happening when NaOH dissolves?s happening when NaOH dissolves?

Add HAdd H22OO

NaOH molecules close NaOH molecules close together, not interactingtogether, not interacting

NaOH molecules pulled NaOH molecules pulled apart & interact with Hapart & interact with H22O O moleculesmolecules

CalorimetryCalorimetry calculate energy released by NaOH as it calculate energy released by NaOH as it

dissolves in waterdissolves in water

energy lost by NaOH = energy gained by energy lost by NaOH = energy gained by water water • easier to calculate from Heasier to calculate from H22O perspectiveO perspective

Q = mcQ = mcTT

Q = 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 22temperature of water increased from 22C C to 30to 30CC

what mass to use? what mass to use?

temp change was for water, so use mass Htemp change was for water, so use mass H22O O

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

30C -22C = 8C = T

m= 100 g

C H20 = 4.18J/gC

Q = mcQ = mcTT

Q = (100 g)(4.18 _Q = (100 g)(4.18 _J J )(8)(8C)C)

g g CC

Q = 3344Q = 3344 J

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