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Part 2
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What are the three states of matter?
What are their changes called?
Did you know?
During a race, an athlete can burn a lot of calories that either do work or are
released as heat
The evaporation of sweat from your skin helps to rid your body of excess heat.
HOW?
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Each change s associated with a change in HEAT.
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1. Heat of Fusion
(solid to liquid)
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2. Heat of Solidification
(liquid to solid)
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3. Heat of Vaporization
(liquid to gas)
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4. Heat of Condensation (gas to liquid)
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5. Heat of Solution
(solute dissolves in solvent)
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What happens if you place an ice cube on a table in a warm
room?
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The molar heat of fusion (∆Hfus) is the heat absorbed by one
mole of a solid substance as it melts to a liquid at a
constant temperature.
Heat is GAINED from
Surroundings.
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What happens when you put liquid water into a freezer?
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The molar heat of solidification (∆Hsolid) is the heat lost
when one mole of a liquid solidifies at a constant
temperature.
Heat is LOST to
surroundings.
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 The
quantity of heat absorbed by a melting solid is
exactly the same as the quantity of heat released
when the liquid solidifies; that is, ∆Hfus = –∆Hsolid.
 Ice
to Liquid ; Liquid to Ice
 H2O (s)  H2O (l)
∆Hfus = 6.01 kJ/mol
 H2O (l)  H2O (s)
∆Hsolid = -6.01 kJ/mol
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Units: KJ/mol
∆Hfus= 6.01 kJ/mol
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We are working backwards in this problem..
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PAGE 521 # 21
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∆Hfus= 6.01 kJ/mol
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What happens if we add heat to a pot of water?
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The amount of heat necessary to vaporize one mole of a
given liquid is called its molar heat of vaporization (∆Hvap).
Heat is GAINED
from surroundings.
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What happens when you take a cold glass of water and
place it in a warm room?
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The amount of heat released when 1 mol of vapor
condenses at the normal boiling point is called its molar
heat of condensation (∆Hcond).
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Heat is LOST to
surroundings.
 The
quantity of heat absorbed by a vaporizing liquid
is exactly the same as the quantity of heat released
when the vapor condenses; that is, ∆Hvap = –
∆Hcond.
 H2O (l)
 H2O (g)
 H2O (g)  H2O (l)
∆Hvap = 40.7 kJ/mol
∆Hcond = -40.7kJ/mol
∆Hvap = 40.7 KJ/mol
Ignore the temp and pressure! This is
important, but is not required to do
calculation!!
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Page 524 # 24
What is the heat of solidification for ethanol?
What is the heat of condensation for methanol?
During the formation of a solution, heat is
either released or absorbed.
The enthalpy change caused by dissolution of
one mole of substance is the molar heat of
solution (∆Hsoln).
NH4NO3 dissolved in water becomes cold. So cold, frost will form on
outside of container! This is what is in a cold pack.
CaCl2 dissolved in water produces heat. This is what is in a hot
pack.
∆Hsoln = -445.1 KJ/mol
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Page 526 # 26
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∆Hsoln = 25.7KJ/mol
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Study for Test. It is Next Thursday October 2!
Problems:
 Page 526 #27-31
 Page 535 #55
 Study the practice
problems we did today!
 Study Practice problems
from Notes #5 and previous homework!
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