Science Thermal energy

​Lesson: "Intro to Thermal Energy"

READING MATERIAL

WHAT IS THERMAL ENERGY?

The atoms or molecules that make up substances are always vibrating as a result of
thermal energy. When a substance is hotter, that means its atoms or molecules are
vibrating faster. Thermal energy always moves from a hotter area to a colder area.
Adding or removing thermal energy can cause a substance to change from one state
to another, and chemical reactions can cause thermal energy to increase or decrease.

To better understand thermal energy…

LET’S BREAK IT DOWN!

What is thermal energy?

All matter is made up of particles,

either atoms or molecules, and

these particles are constantly

vibrating. The energy of these

moving particles is called thermal

energy and is related to the

temperature of the substance.

Temperature measures the average

kinetic (or motion) energy of the

particles within a substance. Temperature measures an average because the particles within a

substance do not all move at exactly the same speed. The particles in hotter substances are

moving faster, whereas the particles in colder substances are moving slower.

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Changing States of Matter

Thermal energy and temperature

help us explain how matter changes

from one state to another. Think

about water as an example. The

molecules in ice (solid water) are

packed tightly together and just

vibrating in place. The temperature

of ice is low, 0°C or lower. The

molecules in liquid water vibrate

more and are constantly bumping into and sliding past each other. The temperature of liquid

water is higher than ice, between 0°C and 100°C. The molecules in water vapor, a gas, move so

fast that they spread far about. The temperature of water vapor, which is also called steam, is

higher than liquid water, 100°C or higher. Matter can change state when thermal energy is

transferred into or out of the substance. Ice melts and liquid water boils as thermal energy is

added. Water vapor condenses and liquid water freezes as thermal energy is removed. Thermal

energy always moves from a hotter area to a colder area, and this movement of thermal

energy is called heat.

Reducing Thermal Energy Transfer

Transferring thermal energy can be

very useful when we want to heat

something up or cool something

down. But sometimes we want to

keep hot things hot or cold things

cold. In these cases, we want to

reduce the amount of thermal

energy that is transferred into or out

of a substance. We can do this by

surrounding the substance, such as hot coffee, with another material called an insulator that

does not transfer thermal energy very well. These materials, such as cardboard or foam, often

have lots of air space. Because the air molecules in that space are not close together, they do

not transfer thermal energy well. Thermoses use a vacuum (a space that contains no air

molecules) to insulate hot liquids. With no molecules to bump into each other, thermal energy is

transferred very slowly across the vacuum.

Chemical Reactions That Cause Thermal Energy
Changes

Chemical reactions can cause

changes in thermal energy by

absorbing or releasing thermal

energy. Reactions that release

thermal energy heat up their

surroundings by causing particles to

vibrate faster. These reactions can

be used to heat food or your hands

and feet on a cold day. A fire is a

great example of a chemical reaction that releases thermal energy, along with light energy.

Reactions that absorb thermal energy cool down their surroundings by causing particles to

vibrate slower. This kind of reaction is used in instant cold packs that you might put on a sports

injury.

Thermal Energy in Everyday Life

We can find many examples of using

thermal energy in our everyday lives.

Any time you heat up or cool down

something, you are using thermal

energy. Heating and cooling foods

provides some familiar examples.

Baking chocolate chip cookies

involves transferring thermal energy

to the cookie dough, which causes

the chocolate chips to change from a solid to a liquid. When the cookies cool, they transfer

thermal energy to the air around them, and the chips return to a solid. Popcorn pops because

the microwaves increase the thermal energy of the water molecules inside the kernels. The

water turns to vapor, and the increasing pressure causes the kernels to explode. When you

make ice pops, the freezer lowers the thermal energy of the liquid, turning it into ice. You can

also see examples of thermal energy changes on a ski trip. Artificial snow is made by lowering

the thermal energy of water droplets, and hand warmers use a chemical reaction that releases

thermal energy to warm your hands.

INTRO TO THERMAL ENERGY VOCABULARY

Thermal energy

The motion of atoms or molecules within a substance.

Temperature

The average kinetic energy of the atoms or molecules within a substance.

Kinetic energy

Energy of motion.

Solid

Matter in which atoms are closely spaced and vibrate in a fixed position.

Liquid

Matter in which atoms are constantly moving around and bumping into each other.

Gas

Matter in which atoms vibrate so much that they are far apart.

INTRO TO THERMAL ENERGY DISCUSSION QUESTIONS

Why do hot objects have high temperatures?

Temperature measures the average kinetic energy of the atoms or molecules that make up an
object. As thermal energy is added to an object, the object’s molecules move faster. When the
molecules move faster, they have more kinetic energy. So the temperature increases.

What happens to the molecules that make up a chocolate chip as it is heated
in the oven?

As thermal energy is transferred to the chocolate, its molecules vibrate faster and faster.
Eventually they vibrate fast enough that they start to slide past each other and move around. As
this happens, the chocolate changes from a solid to a liquid.

​

Multiple Choice

2. Which would have more thermal energy?

• 2. a cup of room-temperature

• 2. cold water?

Multiple Choice

In which substance are molecules moving the fastest?

• a. Solid water (ice)

• b.Liquid water

• c. Water vapor (gas)

Open Ended

Exit Ticket

Describe the difference between a hot cup of water and a cold one in terms of thermal energy.

​1. Thermal energy: The motion of atoms or molecules within a substance.

2. Temperature: The average kinetic energy of the atoms or molecules within a substance.

3. Kinetic energy: Energy of motion.

4. Solid: Matter in which atoms are closely spaced and vibrate in a fixed position.

5. Liquid: Matter in which atoms constantly move around and bump into each other.

6. Gas: Matter in which atoms vibrate so much that they are far apart.

7. Water vapor: Water in gas form.

8. Water in gas form is when matter loses thermal energy and changes from a gas to a liquid.

9. Heat: The transfer of thermal energy from a hotter area to a colder area.

10. Chemical reaction: A process that creates new substances from existing substances and can absorb or release thermal energy.