This explains the Science of Phase Change

1. Phase change

2. During phase changes, two physical states of the
substance exist at the same time.
When addition or removal of heat is stopped at
this temperature, the two physical states will
interconvert from one state to the other, and will
be at equilibrium.
PHASE CHANGE

3. PHASE CHANGE

4. PHASE CHANGE

5. PHASE CHANGE

6. Solid-liquid
equilibrium

7. •

8. Substance ΔHfus (kJ/mol)
Argon (Ar) -190.0 1.3
Benzene (C6H6) 5.5 10.9
Diethyl ether (C2H5OC2H5) -116.2 6.9
Ethanol (C2H5OH) -117.3 7.61
Mercury (Hg) -39.0 23.4
Methane (CH4) -183.0 0.84
Water (H2O) 0.0 6.01

9. •
Heat Change q

10. Liquid-VAPOR
equilibrium

11. It is defined as the energy (usually in kilojoules)
required to vaporize 1 mole of a liquid at a given
temperature, usually, at the boiling point.

12. Substance ΔHvap (kJ/mol)
Argon (Ar) -186.0 6.3
Benzene (C6H6) 80.1 31.0
Diethyl ether (C2H5OC2H5) 34.6 26.0
Ethanol (C2H5OH) 78.3 39.3
Mercury (Hg) 357.0 59.0
Methane (CH4) -164.0 9.2
Water (H2O) 100.0 40.8

13. solid-VAPOR
equilibrium

14. It is the amount of energy that must be added to a
mole of solid at constant pressure to turn it directly
into a gas, without passing through the liquid phase
This enthalpy change associated with sublimation
is always greater than that of vaporization even if
both sublimation and evaporation involve changing
a substance into its gaseous state because in
sublimation, the starting physical state of the
substance is the solid state, which is lower in energy
than the liquid state where vaporization starts.

16. Heat change with
temperature
change

17. •
Specific Heat of Substance Cp

18. The specific heat of a substance differs for the solid,
liquid, and gaseous states.
Water as an example, has the following specific heat at
different phases:
H2O(l) = 4.18 J / g °C
H2O(s) = 2.06 J / g °C
H2O(g) = 2.02 J / g °C
Specific Heat of Substance Cp

19. •
Heat Change q

20. Sample problems

21. Sample Problem 1: пfA
T A sOR fD
☑ ☑
You found a piece of Cu weighing 3.10 g imbedded in an
ice block. How much heat is absorbed by the piece of
metal as it warms in your hand from the temperature of
the ice block at 1.5°C to your body temperature of 37.0°
C? The specific heat of Cu is 0.385 J/g-°C. Assume that
the metal is pure.
Sample problems

22. •
Sample problems

23. Sample Problem 2: heat of fusion
How much energy is required to change 2,600 grams of
ice at 0°C into water at the same temperature?
Sample problems

24. •
Sample problems

25. Sample Problem 3: heat of vaporization
How much energy is required to change 2,600 grams of
water at 100°C into steam at the same temperature?
Sample problems

26. •
Sample problems

27. Sample Problem 4: energy requirement
Calculate the amount of energy (in kJ) needed to heat
346 grams of liquid water from 0°C to 182°C . Assume
that the specific heat of water is 4.184 J/g °C over the
entire liquid range and the specific heat of steam is 1.99
J/g °C .
Sample problems

28. Solution in Sample Problem 4:
Step 1: Heating of water from 0°C to 100°C
q1 = m Cp ΔT
= (346 g) (4.184 J/g °C ) (100°C –
0°C )
= 144, 766.4 J
= 144.766 kJ
Sample problems

29. •
Sample problems

30. Solution in Sample Problem 4:
Step 3: Heating steam from 100°C to 182°C
q3 = m Cp ΔT
= (346 g) (1.99 J/g °C ) (182°C –
100°C)
= 56, 460.28 J
= 56.460 kJ
Sample problems

31. Solution in Sample Problem 4:
The overall energy required is given by
qT = q1 + q2 + q3
= (144.766 + 784.074 + 56.460) kJ
= 985.3 kJ
Sample problems

32. SImple problems

33. Problem 1:
Calculate the heat released when 68.0 grams of steam at
124°C is converted to water at 45°C.
Simple problems

34. Problem 2:
Calculate the amount of heat that must be absorbed by
10.0 grams of ice at 2°C to convert it to liquid water at
60°C.
Given:
Cp (ice) = 2.1 J/g °C
Cp (water) = 4.18 J/g °C
Hfus = 6.0 kJ/mol
Simple problems

35. Problem 3:
Calculate the amount of heat needed to melt 2.00
kilograms of iron at its melting point (1,809 K), given
that: Hfus = 13.80 kJ/mol.
Simple problems

36. •
Simple problems

37. Problem 5:
How much energy (heat) is required to convert 52.0
grams of ice at 10°C to steam at 100°C?
Given:
Hfus = 6.02 kJ/mol
Hvap = 40.7 kJ/mol
Cp (ice): 2.09 J/g °C
Cp (water): 4.18 J/g °C
Cp (steam): 1.84 J/g
°C
Simple problems

38. Problem 6:
Acetic acid has a heat of fusion of 10.8 kJ/mol and a heat
of vaporization of 24.3 kJ/mol. What is the expected
value for the heat of sublimation of acetic acid?
Simple problems