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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 Inter-

Molecular 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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Solid

Melting

Liquid

GasVaporizing

Tem

pe

ratu

re

Energy

HEATING CURVE

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COOLING CURVE

SolidTem

pe

ratu

re

Freezing

Liquid

Gas

Condensing

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

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/g ̊C or

Graphite 0.709J/g ̊C

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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.

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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UNITS OF ENERGY (HEAT)

Q = mc∆T

Q = mHv

Q = mc∆T

Q = mHf

Q = mc∆T

HOW TO SOLVE HEAT CAPACITY PROBLEMS:

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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 ConstantsFor 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

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Essential Question:

Explain the difference between

endothermic and exothermic

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

Endothermic Reactions

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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

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Hot steam from your shower

cools and condenses on the

bathroom mirror