Introduction to Matter – Course 3
7.3 Changes of State
What Happens When Heat is Transferred to a
Substance?
THERMAL ENERGY AND HEAT
Thermal Energy- the total kinetic and potential energy of the
particles in an object.
Heat- the transfer of thermal energy from a warmer object to a
cooler object.
HOT
COLD
When heat is transferred to a substance, the substance undergoes
an increase in temperature, a change of state, or both.
Changes of State
Thermal Energy
The two pots of hot water shown are both at 99ºC, but one of them has
about twice as much thermal energy as the other. Why does the larger pot
have more thermal energy?
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Physical Changes
Physical Property- a characteristic of a substance that can be
observed without changing it into another substance.
Physical Change – a change in a substance that changes the
characteristics of the substance without changing the substance
itself.
Ex. Of Physical Changes:
Increase of Temperature
Change of State
Water is still water if is is hot, cold, frozen, or water vapor.
Boiling Water, Cold Water, Ice, and Water Vapor are all just Water
Physical Properties
Identify some of the physical properties of these rocks versus the
sponge.
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Assess Your Understanding
1.a. What determines an objects temperature?
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b. How does thermal energy differ from temperature?
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What Happens to a Solid as it Melts?
Melting – the change in state from a solid to a liquid.
Melting Point- the specific temperature at which a solid turns into
a liquid.
•At a solid’s melting point, its particles vibrate so fast that they
break free from their fixed positions.
Changes of State
Melting
Which circle of molecules represents water, and which represents ice?
Describe how ice and liquid water differ in the arrangement
of their molecules.
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Freezing
Freezing- Change from a liquid to a solid
Freezing Point- the particles move so slowly that they begin to
take on fixed positions.
APPLY IT!
In metal casting a liquid metal is poured into a container called a mold.
The mold gives a shape to the metal when it cools and hardens.
1. How does the metal casting make use of the different characteristics
Of liquids and solids?
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Assess Your Understanding
2.a. The change in state from a solid to a liquid is called
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b. How does what happens to the particles in a substance during
melting differ from what happens in freezing?
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What Happens to a Substance
That Becomes Gas?
Evaporation and Boiling
Vaporization- When a liquid becomes a gas.
-Vaporization occurs when the particles in a liquid gain enough
energy to move independently and form a gas.
Two Types of Vaporization
1. Evaporation- vaporization that occurs at the surface of a
liquid. Ex. A puddle of water, some molecules of
water at the surface escape as the puddle gains
energy from the sun, ground, or air.
2.Boiling- vaporization that occurs both at the surface and
below the surface.
Boiling Point- The temperature at which a liquid boils.
Changes of State
Types of Vaporization
Liquid water changes to water
vapor by either evaporation or
boiling. What are the types of
vaporization occurring in each flask?
Compare and Contrast boiling and Evaporation.
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Which flask does water vaporize from first? Why?
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Condensation
Condensation- The change in state from a gas to a liquid.
When warm water vapor from your shower, reaches a cooler
surface such as the mirror in your bathroom, the water vapor
condenses into liquid droplets.
Condensation occurs when the particles in a gas lose enough
energy to form a liquid.
Clouds are formed when water vapor in the atmosphere
condenses into tiny liquid droplets. When the droplets get heavy
enough they fall to the ground as rain.
Steam, clouds, and fog are not water vapor, they are tiny
droplets of liquid water suspended in air.
Changes of State
Liquid to a Gas
The graph shows the temperature of a small pot of water on a stove set
to high heat.
Changes of State- Do the Math! Analyzing Data
Temperature and Changes
of State
A sealed beaker of ice at –10ºC
was slowly heated to 110ºC. The
changes in the temperature of
the water over time were
recorded. The data were plotted
on the graph.
1. What two variables are
plotted on the graph?
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2. What change of state is occurring during segment B?__________________
Segment D?______________
3. In which segment, A or E, do the water molecules have more thermal energy?
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Sublimation
Sublimation- When a solid changes directly into a gas.
The surface particles of a solid gain enough energy that they
form a gas. They do NOT pass through the liquid state!
A fog machine uses dry ice to create fog at this rock concert.
Why does fog form near dry ice?
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Changes of State
The Changing States of Water
Assess Your Understanding
3a. What is dry ice?
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b. If you allowed dry ice to stand in a bowl at room temperature
for several hours, what would be left?
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