1 THERMOCHEMISTRY or Thermodynamics. 2 Energy & Chemistry ENERGY is the capacity to do work or...

1

THERMOCHEMISTRYTHERMOCHEMISTRYoror

ThermodynamicsThermodynamics

THERMOCHEMISTRYTHERMOCHEMISTRYoror

ThermodynamicsThermodynamics

2

Energy & ChemistryEnergy & ChemistryEnergy & ChemistryEnergy & Chemistry

ENERGYENERGY is the capacity to do is the capacity to do work or transfer heat.work or transfer heat.

HEATHEAT is the form of energy is the form of energy that flows between 2 objects that flows between 2 objects because of their difference in because of their difference in temperature.temperature.

Other forms of energy —Other forms of energy —

• lightlight

• electricalelectrical

• kinetic and potentialkinetic and potential

3

Energy & ChemistryEnergy & Chemistry

All of thermodynamics depends on All of thermodynamics depends on the law of the law of

CONSERVATION OF ENERGYCONSERVATION OF ENERGY..

• The total energy is unchanged in The total energy is unchanged in a chemical reaction.a chemical reaction.

• If PE of products is less than If PE of products is less than reactants, the difference must be reactants, the difference must be released as KE.released as KE.

4

Internal Energy (E)Internal Energy (E)Internal Energy (E)Internal Energy (E)

• PE + KE = Internal energy (E or U)

Int. E of a chemical system depends on

• number of particles

• type of particles

• temperature

5Potential & Kinetic Potential & Kinetic EnergyEnergy

Potential & Kinetic Potential & Kinetic EnergyEnergy

6Thermo-Thermo-dynamicdynamic

ss

Thermo-Thermo-dynamicdynamic

ssthe science of

heat transfer (molecular molecular motionsmotions).

Heat transfers until thermal

equilibrium is established.

7

Directionality of Heat TransferDirectionality of Heat Transfer• Heat always transfer from hotter object to

cooler one. Heat lost = heat gained

•EXOthermic: heat transfers from SYSTEM to SURROUNDINGS.

T(system) goes downT(system) goes downT(surr) goes upT(surr) goes up

(until it reaches (until it reaches equilibriumequilibrium

8

Directionality of Heat TransferDirectionality of Heat Transfer• Heat always transfer from hotter object to

cooler one. Heat lost = heat gained

•ENDOthermic: heat transfers from SURROUNDINGS to the SYSTEM.

T(system) goes upT(system) goes upT (surr) goes downT (surr) goes down

9

ENERGY TRANSFERENERGY TRANSFER

1.IDENTIFY SURROUNDINGS AND SYSTEM.

2.EXOTHERMIC OR ENDOTHERMIC ?

10WORK?

11

Heat is NOT temperature

The increased volume with temperature causes the mercury to rise

12

UNITS OF ENERGYUNITS OF ENERGYUNITS OF ENERGYUNITS OF ENERGY1 calorie = heat required to raise 1 calorie = heat required to raise

temp. of 1.00 g of Htemp. of 1.00 g of H22O by 1.0 O by 1.0 ooC.C.

1000 cal = 1 kcal1000 cal = 1 kcal

= 1 Calorie (a food “calorie”)= 1 Calorie (a food “calorie”)James JouleJames Joule1818-18891818-1889

But we use the unit called But we use the unit called

the the JOULEJOULE1 cal = 4.184 joules1 cal = 4.184 joules

13

HEAT TRANSFER

The quantity of heat transferred depends on:

1.The quantity of material

2. The size of the temperature change

3. The identity of the material

gaining or losing heat

14

HEAT CAPACITYHEAT CAPACITY

Specific heat =

The heat required to raise 1 g of substance 1 ˚K.

Specific heat capacity =

heat lost or gained by substance (J)

(mass, g)(T change, K)

15

16

Heat Calculations

Specific heat capacity (J/ g * K)

Heat transfer (J)

Mass of substance (g)

Change in temperature (K)

q = C * m * ∆T

17

18

19

Specific Heat Specific Heat CapacityCapacity

Specific Heat Specific Heat CapacityCapacity

If 25.0 g of Al cool from 310 If 25.0 g of Al cool from 310 ooC C to 37 to 37 ooC, how many joules of C, how many joules of

heat energy are lost by the Al?heat energy are lost by the Al?

20

Specific Heat Capacity

Specific Heat Capacity

where ∆T = Tfinal - Tinitial

q = (0.897 J / g•K)(25.0 g)(37 - 310)K

q = - 6120 J

Notice that the negative sign on q signals heat “lost by” or transferred

OUT of Al.

Notice that the negative sign on q signals heat “lost by” or transferred

OUT of Al.

21Change of State: Change of State: Heat of FusionHeat of Fusion

Change of State: Change of State: Heat of FusionHeat of Fusion

Ice + 333 J/g (heat of fusion) -----> Liquid water

q = (heat of fusion)(mass)

constant T

22

Heat waterHeat water

Evaporate waterEvaporate water

Melt iceMelt ice

Heating/Cooling Curve for Water

Heating/Cooling Curve for Water

Note that T is Note that T is constant as ice meltsconstant as ice melts

Note that T is Note that T is constant as ice meltsconstant as ice melts

23

Heat of fusion of ice = 333 J/gSpecific heat of water = 4.2 J/g•KHeat of vaporization = 2260 J/g

Heat of fusion of ice = 333 J/gSpecific heat of water = 4.2 J/g•KHeat of vaporization = 2260 J/g

What quantity of heat is required to melt 500. g of ice and heat the water to steam at 100 oC?

Heat & Changes of StateHeat & Changes of StateHeat & Changes of StateHeat & Changes of State

+333 J/g+333 J/g +2260 J/g+2260 J/g

24

1. melt ice 0 oC

q = (500. g)(333 J/g) = 1.67 x 105 J

2. water from 0 oC to 100 oC

q = (500. g)(4.2 J/g•K)(100 - 0)K = 2.1 x 105 J

3. To boil water 100 oC

q = (500. g)(2260 J/g) = 1.13 x 106 J

4. Total q = 1.51 x 106 J = 1510 kJ

Heat & Changes of StateHeat & Changes of StateHeat & Changes of StateHeat & Changes of State

25CalorimeterCalorimeter