The system is the specific part of the universe that is of interest in the study. open mass &...
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The system is the specific part of the universe that is of interest in the study. open mass & energy Exchange: closed energy isolated nothing SYSTEM SURROUNDINGS 6.2
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Transcript of 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
