the system is the specific part of the universe that is of interest in the study. open mass &...

The system is the specific part of the universe that is of interest in the study.

open

mass & energyExchange:

closed

energy

isolated

nothing

SYSTEMSURROUNDINGS

6.2

DIRECTION OF HEAT FLOW

Surroundings

ENDOthermicqsys > 0

EXOthermicqsys < 0

System

Kotz, Purcell, Chemistry & Chemical Reactivity 1991, page 207

System

H2O(s) + heat H2O(l)

melting

H2O(l) H2O(s) + heat

freezing

ENERGY OF ACTIVATION

ENERGY OF ACTIVATION

HEAT GAINED = HEAT LOST

DH = mDTCp

M= mass

DT= change in temperature

Cp= specific heat

Caloric Values

Food joules/grams calories/gram Calories/gram

Protein 17 000 4000 4

Fat 38 000 9000 9

Carbohydrates 17 000 4000 4

Smoot, Smith, Price, Chemistry A Modern Course, 1990, page 51

1000 calories = 1 Calorie

"science" "food"

1calories = 4.184 joules

HEATING CURVESTe

mp

erat

ure

(oC

)

40

20

0

-20

-40

-60

-80

-100

120

100

80

60

140

Time

Melting - PE

Solid - KE

Liquid - KE

Boiling - PE

Gas - KE

A B warm iceB C melt ice (solid liquid)C D warm waterD E boil water (liquid gas)E D condense steam (gas liquid)E F superheat steam

HEATING CURVE FOR WATER(PHASE DIAGRAM)

140

120

100

80

60

40

20

0

-20

-40

-60

-80

-100

Tem

pera

ture

(oC

)

Heat

BP

MP

A

BC

D E

F

Heat = m x Cfus

Cf = 333 J/g

Heat = m x Cvap

Cv = 2256 J/g

Heat = m x DT x Cp, liquid

Cp = 4.184 J/goC

Heat = m x DT x Cp, solid

Cp (ice) = 2.077 J/goC

Heat = m x DT x Cp, gas

Cp (steam) = 1.87 J/goC

HEATING CURVES

Temperature Changechange in KE (molecular motion) depends on heat capacity

• Heat Capacity– energy required to raise the temp of 1 gram of a

substance by 1°C– “Volcano” clip -– water has a very high heat capacity

Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

HEATING CURVES

Phase Changechange in PE (molecular arrangement)temp remains constant

• Heat of Fusion (Hfus)– energy required to melt 1 gram of a substance at its

m.p.

Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

HEATING CURVES

Heat of Vaporization (Hvap)energy required to boil 1 gram of a substance at its b.p.

usually larger than Hfus…why?

• EX: sweating, steam burns, the drinking bird

Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

HUMOR

A small piece of ice which lived in a test tube fell in love with a Bunsen burner.

“Bunsen! My flame! I melt whenever I see you” said the ice.

The Bunsen burner replied” “It’s just a phase you’re going through”.

CH4 + 2 O2 ® CO2 + 2 H2O + 802.2 KJ

If 10. 3 grams of CH4 are burned completely, how much heat will be produced?

15

10. 3 g CH4

16.05 g CH4

1 mol CH4

1 mol CH4

802.2 kJ

= 514 kJ

ENTROPY (ABBREVIATED “S”)

Entropy is a measure of disorder, and is measured in units of J/mol.K; and there are no negative values of entropy

Entropy (S) is a measure of the randomness or disorder of a system.

- Page 570

Entropy of the gas is greater than the solid or liquid

Entropy is increased when a substance is divided into parts

Entropy increases when there are more product molecules than reactant molecules

Entropy increases when temperature increases

Entropy (S) is a measure of the randomness or disorder of a system.

order SdisorderS

If the change from initial to final results in an increase in randomness

DS > 0

For any substance, the solid state is more ordered than the liquid state and the liquid state is more ordered than gas state

Ssolid < Sliquid << Sgas

H2O (s) H2O (l) DS > 0

18.3

EQUAL MASSES OF HOT AND COLD WATER

Thin metal wall

Insulated box Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 291

WATER MOLECULES IN HOT AND COLD WATER

Hot water Cold Water90 oC 10 oC

Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 291

WATER MOLECULES IN THE SAME TEMPERATURE WATER

Water(50 oC)

Water(50 oC)

Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 291

The amount of heat required to raise the temperature of one gram of substance by one degree Celsius.

Specific Heat

In football, as in Hess's law, only the initial and final conditions matter.A team that gains 10 yards on a pass play but has a five-yard penalty,has the same net gain as the team that gained only 5 yards.

initial positionof ball

final positionof ball

10 yard pass

5 yard penalty

5 yard net gain