ThermodynamicsThermodynamicsStandard 7Standard 7

Chemistry.Chemistry.

Ms. Siddall.Ms. Siddall.

Chemical ThermodynamicsChemical Thermodynamics = the = the movement of heat in a chemical movement of heat in a chemical reaction.reaction.

TemperatureTemperature = a measure of the = a measure of the average kinetic energy of particle average kinetic energy of particle motionmotion

HeatHeat = The = The transfertransfer of energy from of energy from a hotter object to a colder object a hotter object to a colder object (sometimes called ‘heat flow’)(sometimes called ‘heat flow’)– temperature measures energytemperature measures energy– Heat measures energy transferHeat measures energy transfer

Standard 7a: ‘heat flow’

Summary 1Summary 1

Describe the difference between Describe the difference between heat and temperatureheat and temperature

Energy transferEnergy transfer Particle vibrations increase when a Particle vibrations increase when a

particle gains energyparticle gains energy Vibrations are transferred to Vibrations are transferred to

surrounding particlessurrounding particles

Summary 2Summary 2Describe how energy is transferred Describe how energy is transferred

between atoms.between atoms.

Identifying heat transferIdentifying heat transfer:: SystemSystem: experiences a change: experiences a change SurroundingsSurroundings: causes a change: causes a change

e.xe.x. hot coffee (system) cools because it . hot coffee (system) cools because it transfers heat to the air, the cup, the table transfers heat to the air, the cup, the table & the whole universe! (surroundings)& the whole universe! (surroundings)

Summary 3Summary 3

Consider an ice cube dropped into Consider an ice cube dropped into a glass of warm water. a glass of warm water.

Ice cube = systemIce cube = system Water = surroundingsWater = surroundings1.1. Does heat flow Does heat flow intointo the system the system

or or out ofout of the system? the system?2.2. What is What is gaining gaining energy (system energy (system

or surroundings)?or surroundings)?

Endothermic ProcessEndothermic Process: A process in : A process in which energy is absorbed.which energy is absorbed.

Example: Example: Water boilingWater boiling– HH22OO(l)(l) + heat + heat H H22OO(g)(g)

In an endothermic process heat is a In an endothermic process heat is a reactant.reactant.

Standard 7b: exothermic & endothermic process

reactants product

Summary 4 Summary 4 In an endothermic process which has In an endothermic process which has

more energy; reactants or products?more energy; reactants or products?

Exothermic ProcessExothermic Process: A process in : A process in which energy is released.which energy is released.

Example:Example:– A fireA fire

– 3C + 2O3C + 2O22 heat + 2CO + CO heat + 2CO + CO22

In an exothermic process heat is a product

reactants products

Summary 5 Summary 5 In an exothermic process which has In an exothermic process which has

more energy, reactants or products?more energy, reactants or products?

Energy Energy diagramdiagram

Incr

easi

ng e

nerg

y

HH22OO(g)(g)

exoth

erm

ic HH22OO(l)(l) en

doth

erm

ic

Summary Summary 66

Draw an energy Draw an energy diagram for the diagram for the campfire reaction. campfire reaction. – Show reactants and Show reactants and

products.products.– Draw only Draw only oneone arrow arrow

from reactants to from reactants to products and label products and label the arrow the arrow (endothermic or (endothermic or exothermic)exothermic)

Transition State energy diagramTransition State energy diagram

reactants

products

Transition state

en

erg

yactivation energy = energy needed to form transition state (activated

complex)

Energy released when products

form

Total energy released during

reaction

Transition StateTransition State:: An An intermediateintermediate state that can occur during a reactionstate that can occur during a reaction

Also called an ‘activated complex’Also called an ‘activated complex’ An exothermic reaction is not always

spontaneous because energy is needed to form a transition state.

e.x. a spark is needed to start a fire

SummarySummary 7 7 Draw a transition state energy diagram Draw a transition state energy diagram

for an endothermic reactionfor an endothermic reaction

Measuring heat flowMeasuring heat flow.. Energy is measured in joules (J) or Energy is measured in joules (J) or

calories (cal)calories (cal) ExampleExample: 334J of energy are : 334J of energy are

needed to melt 1g of ice.needed to melt 1g of ice. 1 calorie (c) = 4.18J1 calorie (c) = 4.18J 1 food calorie (C) = 1000 calories 1 food calorie (C) = 1000 calories

= 4180J= 4180J

Summary 8Summary 8If your body burns about 2,000 food If your body burns about 2,000 food

calories a day, approximately how calories a day, approximately how many joules of energy is that?many joules of energy is that?

Showing a change in energyShowing a change in energy:: SS(s)(s) + O + O2(g)2(g) SO SO2(g)2(g) + energy + energy

SS(s)(s) + O + O2(g)2(g) SO SO2(g)2(g) + 297KJ + 297KJ

SS(s)(s) + O + O2(g)2(g) SO SO2(g)2(g) ∆H = -297KJ ∆H = -297KJ

Energy released = exothermicKJ = kilojoules = 1000J

-∆H = exothermic+∆H = endothermic∆H = change in enthalpy

Enthalpy = energy/heat

NN2(g)2(g) + 2O + 2O2(g)2(g) 2NO 2NO2(g)2(g) ∆H = + 68KJ ∆H = + 68KJ

NN2(g)2(g) + 2O + 2O2(g)2(g) + 68KJ + 68KJ 2NO 2NO2(g)2(g)

Endothermic reactionEnergy is a reactant

Summary 9Summary 9

Write an equation to show water Write an equation to show water melting. Use ∆H to show energy. melting. Use ∆H to show energy.

(it takes 5.9kJ of energy to melt (it takes 5.9kJ of energy to melt ice)ice)

Is ∆H negative or positive? Why?Is ∆H negative or positive? Why?

Phase ChangePhase Change: The : The physical statephysical state of a of a compound changescompound changes

The same compound is observed The same compound is observed before before andand after the change after the change

Example: ice melting Example: ice melting H H22OO(s)(s) H H2200(l)(l)

There is There is no temperature changeno temperature change.. Energy is used to overcome Energy is used to overcome

intermolecular attractions.intermolecular attractions.

Standard 7c: energy of phase change

Summary 10Summary 10

Is the example of ice melting an Is the example of ice melting an endothermic process or an endothermic process or an exothermic process?exothermic process?

gas

liquid

solid bre

ak

latt

ice

stru

cture

bre

ak

hyd

rog

en

b

ond

s

melt

ing

evap

ora

tin

g

Con

den

sin

g

En

erg

y r

ele

ase

d

inte

rmole

cula

r att

ract

ion

s ta

ke o

ver

freezin

g

Physical statePhysical stateexoth

erm

ic

en

doth

erm

ic

Summary 11Summary 11

1.1. In which phase do the molecules In which phase do the molecules have the most energy? (solid, have the most energy? (solid, liquid, or gas)liquid, or gas)

2.2. Is the process of condensing Is the process of condensing endothermic or exothermic?endothermic or exothermic?

3.3. Is the process of vaporization Is the process of vaporization endothermic or exothermic?endothermic or exothermic?

Freezing/boiling point graph for Freezing/boiling point graph for water.water.

Tem

pera

ture

(°C

)

100

0

-10

110

energy

ice

Water (CH2O(l))

steam

melting

ΔΔHfus

boiling

ΔΔHvap

Standard 7d: solving problems

Energy absorbed= Change in temperature

= Change in K.E.

Energy absorbed= no temp

change= physical

change

Summary 12Summary 12

Which two sections of the graph Which two sections of the graph show no temperature change.show no temperature change.

Why is there no temperature Why is there no temperature change in these sections?change in these sections?

Latent Heat of fusion.Latent Heat of fusion. ((latent heat = hidden latent heat = hidden heat)heat)

ΔΔHHfusfus = = The energy The energy releasedreleased when 1g of a when 1g of a

substance is frozen substance is frozen OROR the energy the energy neededneeded when 1g of a substance is melted.when 1g of a substance is melted.

ΔΔHHfusfus = enthalpy of fusion (J/g)= enthalpy of fusion (J/g)

• Fusion = freezing Fusion = freezing (liquid (liquid solid) solid) • also used for also used for meltingmelting (solid (solid liquid) liquid)

Standard 7d: solving problems

Summary 13Summary 13: What does ‘fusion’ mean?: What does ‘fusion’ mean?

Example: freezing waterExample: freezing water

How much energy is released when How much energy is released when

10g water freezes? (10g water freezes? (ΔΔHHfusfusHH22O = O =

334J/g)334J/g)

1g H2O(s)

334J = 3340J= 3.34kJ

10g H2O(s)

Summary 14Summary 14

How much energy is needed to melt How much energy is needed to melt 100g of water? (show calculation)100g of water? (show calculation)

Latent Heat of vaporizationLatent Heat of vaporization

ΔΔHHvapvap = = The energy The energy neededneeded when 1g of a when 1g of a

substance is evaporated substance is evaporated OROR the energy the energy releasedreleased when 1g of a substance is when 1g of a substance is condensed.condensed.

ΔΔHHvapvap = enthalpy of vaporization (J/g)= enthalpy of vaporization (J/g)

• vaporization = evaporating vaporization = evaporating (liquid (liquid gas) gas)

• also used for condensing (gas also used for condensing (gas liquid)liquid)

Summary 15Summary 15

What does vaporization mean?What does vaporization mean? What does condensation mean?What does condensation mean?

How much energy is How much energy is neededneeded to boil to boil

10g water? (10g water? (ΔΔHHvapvapHH22O = 2260J/g)O = 2260J/g)

1g H2O(l)

2260J = 22600J= 22.6kJ= J10g H2O(l)

Example: Boiling waterExample: Boiling water

Summary Summary 1616How much energy is released when How much energy is released when

100g of water vapor is 100g of water vapor is condensed? (show work)condensed? (show work)

Heat Heat

CapacityCapacity.. C C = = specific heat capacityspecific heat capacity

• The amount of heat energy needed The amount of heat energy needed to raise the temperature of 1g of a to raise the temperature of 1g of a substance by 1°Csubstance by 1°C

ExampleExample: : CCHH22OO(l)(l) = 4.18J/g°C = 4.18J/g°C• It takes 4.18J of energy to raise the It takes 4.18J of energy to raise the

temperature of 1g of water by 1°Ctemperature of 1g of water by 1°C

1 calorie = 4.18J1 calorie = 4.18J

Summary 17Summary 17

How much energy is needed to How much energy is needed to raise the temperature of 1g of raise the temperature of 1g of water by 1water by 1°°C? (give your answer C? (give your answer in joules in joules andand calories) calories)

Example.Example.

How much energy is needed to raise How much energy is needed to raise the temperature of 5g water from the temperature of 5g water from 22°C to 24°C? (C22°C to 24°C? (CHH22OO(l)(l) = 4.18J/g°C) = 4.18J/g°C)

2°C°C5g H2O(l) = 41.8J= J4.18J H2O(l)

g °C

How much energy is released when How much energy is released when 10g water cools from 40°C to 30°C? 10g water cools from 40°C to 30°C?

10°C°C10g H2O(l) = 418.J= J4.18J H2O(l)

g °C

Summary 18Summary 18

Unknown compound: heated to 100°C and placed in the cold water

H2O

Thermometer: Measures temperature change for water

Measuring specific heat capacity for different compounds

‘q’=energy released by metal =energy absorbed by water

Summary 19Summary 19

How much energy (q) is released How much energy (q) is released by a metal if the temperature of by a metal if the temperature of 100g of water in the calorimeter 100g of water in the calorimeter rises from 20rises from 20°°C to 30C to 30°°C?C?

Reaction chamber: 3H2 + N2 NH3

heat of reaction is absorbed by water100g H2O

Thermometer: measures temperature change for water• T = exothermic• T = endothermic

Measuring the heat of a reaction: ‘q’(q = energy released or absorbed by water)

ExampleExample: 10g NH: 10g NH33 are produced in the are produced in the above reaction. The temperature above reaction. The temperature rises from 20.0rises from 20.0°°C to 30.0C to 30.0°°C. C.

1.1. Calculate ‘q’ (energy) for the Calculate ‘q’ (energy) for the reaction.reaction.

2.2. Is the reaction endothermic or Is the reaction endothermic or exothermic?exothermic?

3.3. Calculate Calculate ΔΔH (J/g) for this reactionH (J/g) for this reaction

4.4. Calculate Calculate ΔΔH (mol/g) for this reactionH (mol/g) for this reaction

Kinetic energy distribution diagram

Kinetic energy distribution Kinetic energy distribution diagramdiagram TT11 = low temperature = low energy = low temperature = low energy

TT22 = higher temperature = higher = higher temperature = higher energyenergy

EEminmin = minimum energy needed to = minimum energy needed to escape. escape.

– MoreMore T T22 particles have E particles have Eminmin

– LessLess T T11 particles have E particles have Eminmin

Summary 20Summary 20

Explain why more particles Explain why more particles evaporate from a cup of hot water evaporate from a cup of hot water compared to a cup of cold water.compared to a cup of cold water.

Standard 7eStandard 7e: Apply Hess’s : Apply Hess’s Law to calculate enthalpy Law to calculate enthalpy change in a reactionchange in a reaction

Hess’s LawHess’s Law: If a series of reactions are : If a series of reactions are added together the enthalpy change for added together the enthalpy change for the net reaction will be the sum of the the net reaction will be the sum of the enthalpy changes for the individual steps.enthalpy changes for the individual steps.

E.x. NE.x. N2(g)2(g) + 2O + 2O2(g)2(g) 2NO 2NO2(g)2(g)

• NN2(g)2(g) + O + O2(g)2(g) 2NO 2NO(g) (g) ΔΔH = +181kJH = +181kJ

• 2NO2NO(g)(g) + O + O2(g)2(g) 2NO 2NO2(g) 2(g) ΔΔH = -113kJH = -113kJ

Find the sum of the 2 equations…Find the sum of the 2 equations…

NN2(g)2(g) + O + O2(g)2(g) 2NO 2NO(g) (g) ΔΔH = +181kJH = +181kJ

2NO2NO(g)(g) + O + O2(g)2(g) 2NO 2NO2(g) 2(g) ΔΔH = -113kJH = -113kJ

NN2(g)2(g) + O + O2(g) 2(g) + 2NO+ 2NO(g)(g) + O + O2(g)2(g) 2NO 2NO(g) (g) ++ 2NO2NO2(g) 2(g)

NN2(g)2(g) + 2O + 2O2(g) 2(g) 2NO 2NO2(g) 2(g)

ΔΔH =H =

notesnotes: : You can reverse reactions (change sign of You can reverse reactions (change sign of

ΔΔHH)) You can multiply or divide equations (do You can multiply or divide equations (do

same to same to ΔΔHH))

+181kJ+181kJ (-113kJ)(-113kJ) +68kJ+68kJ+ =

Hess summaryHess summary

Complete questions 66, 74, 81 & Complete questions 66, 74, 81 & 84 on page 536 & 53784 on page 536 & 537