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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
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