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UNIT 3 NOTES: PHASE CHANGES
Essential Question
Explain how matter changes
phase and what causes it.
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The State of Matter of a substance depends on
several things
• Attraction between particles called IMF or InterMolecular Forces
• Solids have very high IMF
• Gases have no attraction between molecules
• Liquids have IMF a bit lower than solids
• Energy of the particles
• Space between particles
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PHASE CHANGES
Energy added
Melting: Solid to Liquid
Vaporizing: Liquid to Gas
Sublimation: Solid to Gas
Energy removed
Freezing: Liquid to Solid
Condensing: Gas to Liquid
Deposition: Gas to Solid
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HEATING CURVE
Temperature
Vaporizing
Gas
Liquid
Melting
Solid
Energy
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COOLING CURVE
Temperature
Gas
Condensing
Liquid
Freezing
Solid
Energy
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Energy – causes changes in matter
weightless, odorless, tasteless
All chemical reactions and changes in
state involve either:
a) release of energy, called
Exothermic or
b) absorption of energy called
Endothermic
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The Law of Conservation of Energy
states that in any chemical or
physical process, energy is neither
created nor destroyed.
All the energy is accounted for as
Eth Eph or Ech
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UNIT 3: HEAT CAPACITY NOTES
Essential Question:
Which substance will heat up quicker and
explain why?
Ethanol 2.44J/g̊C or
Graphite 0.709J/g̊C
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Heat Capacity - the amount of heat needed to
increase the temperature of an object
exactly 1 oC
Depends on both the object’s mass and its
chemical composition
Specific Heat Capacity (abbreviated “C”) - the
amount of heat it takes to raise the temperature
of 1 gram of the substance by 1 oC
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The higher a material’s specific
heat the LONGER it take to heat
up and the LONGER it takes to
cool down.
ex. metals have low
specific heat which
means they heat up and
cool down quickly.
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UNITS OF ENERGY (HEAT)
1) A calorie is defined as the quantity of
heat needed to raise the temperature
of 1 g of pure water 1 oC.

1 Food Calorie = 1 kilocalorie = 1000 cal.
2) The Joule, the SI unit of heat and energy
 4.184 J = 1 cal
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HOW TO SOLVE HEAT CAPACITY PROBLEMS:
Q = mc∆T
Q = mHv
Q = mc∆T
Q = mHf
Q = mc∆T
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MEANING OF FORMULA SYMBOLS
Q = heat or energy unit calories or joules (1 cal = 4.18 joules)
m = mass in grams
c = specific heat –it is different for each substance and phase of matter.
J/g°C or cal/g°C
∆T = Change in temperature (Tempfinal – Tempinitial)
Hf = Heat of fusion or melting. Energy needed for a phase change.
Hv = Heat of vaporization or condensation. Energy needed for a phase
change.
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Energy Constants
For water
c solid = 2.1 J/g°C or 0.5 cal/g°C
1 kcal = 1000 cal
c liquid = 4.18 J/g°C or 1 cal/g°C
1 kJ = 1000 J
c vapor = 1.8 J/g°C or 0.44 cal/g°C
Hf = 334 J/g or 80 cal/g
Hv = 2260J/g or 540 cal/g
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UNIT 3 NOTES: ENDOTHERMIC AND EXOTHERMIC
REACTIONS
Essential Question:
Explain the difference between
endothermic and exothermic
reactions
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Endothermic Reactions
Eth flowing into a system from it’s
surroundings:
Q has a positive value
system gains heat (gets warmer)
as the surroundings cool down
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Exothermic reactions
Eth flowing out of a system into it’s
surroundings:
Q has a negative value
system loses heat (gets cooler) as
the surroundings heat up
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IN YOUR NOTEBOOK CREATE THE ENERGY BAR
CHART FOR THIS SITUATION
Hot steam from your shower
cools and condenses on the
bathroom mirror
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