Thermal Energy

Particle Model of Matter

All matter is made up of ___________________

that are __________________________.

Moving particles have ___________ energy.

tiny particles

always moving

kinetic

What is temperature?

• Atoms are in constant motion, even in a solid object.

• The back-and-forth jiggling of atoms is caused by thermal energy, which is a kind of kinetic energy.

What is temperature?

• Temperature measures the kinetic energy per molecule due to random motion.

Thermometers

• A thermometer is an instrument that measures the exact temperature.

• Most thermometers contain either a silvery fluid (mercury) or a red fluid, which is alcohol containing a small amount of red dye.

How does a thermometer work?

• The volume of alcohol in a thermometer contains huge numbers of alcohol molecules.

• As temperature increases, the alcohol molecules move faster and bounce off each other.

• The liquid alcohol expands and takes up more space in the thermometer.

Measuring temperature

• A thermistor is a device that changes its electrical resistance as the temperature changes.

• Some digital thermometers sense temperature by measuring the resistance of electrons passing through wire.

Liquid-crystal thermometers

• Some thermometers contain liquid crystals that change color based on temperature.

• As temperature increases, the molecules of the liquid crystal bump into each other more and more.

• This causes a change in the structure of the crystals, which in turn affects their color.

Temperature

• There are two common temperature scales.

• On the Fahrenheit scale, water freezes at 32 degrees and boils at 212 degrees.

• The Celsius scale divides the interval between the freezing and boiling points of water into 100 degrees.

What is absolute zero?

• Absolute zero is -273°C. • You cannot have a temperature lower than

absolute zero.• Think of absolute zero as the temperature at

which atoms are “frozen.”

Kelvin

• The Kelvin temperature scale is useful in science because it starts at absolute zero.

Fahrenheit (°F) to Celsius (°C) conversion formula:

32 - F95

C

EXAMPLE What is the Celsius value for 65° Fahrenheit?

Celsius (°C) to Fahrenheit (°F) conversion formula:

32 C

95

F

EXAMPLE 200 °C is the same temperature as what value on

the Fahrenheit scale? Solution:

To convert Celsius values to their Kelvin equivalents, use the formula:

273 C K

Water boils at a temperature of 100 °C. What would be the corresponding temperature for the Kelvin scale?

To convert Kelvin values to their Celsius equivalents, use the formula:

273 K C

1a. What is the Celsius value for 212 °F?

1b. What is the Celsius value for 98.6 °F?

1c. What is the Celsius value for 40 °F?

1d. What is the Celsius value for 10 °F?

1e. What is the Fahrenheit value for 0 °C?

1f. What is the Fahrenheit value for 25 °C?

1g. What is the Fahrenheit value for 75 °C?

2. The weatherman reports that today will reach a high of 45 °F. Your friend from Sweden asks what the temperature will be in degrees Celsius. What value would you report to your friend?

3. Your grandmother in Ireland sends you her favorite cookie recipe. Her instructions say to bake the cookies at 190 °C. To what Fahrenheit temperature would you set the oven to bake the cookies?

1. Surface temperatures on the planet Mars range from –89 °C to –31 °C. Express this temperature range in Kelvin.

2. The average surface temperature on Jupiter is about 165K. Express this temperature in degrees Celsius.

3. The average surface temperature on Saturn is 134K. Express this temperature in degrees Celsius.