Temperature Energy and Heat CHAPTER 3 Temperature Energy and Heat 3.1 Temperature

Why is temperature important in chemistry? What is temperature? Why is temperature important in chemistry? How is energy related to temperature? Have students try to define temperature in their own words. Words such as “hot” and “cold” will probably come up. In previous chapters, we have seen how the temperature increases the rate at which sugar dissolves in water. That is one example of how temperature is important in chemistry. When water molecules collide with sugar molecules, they transfer energy. This was mentioned in the previous chapter. Section 3.1 will go into these ideas in greater detail (ex: kinetic energy)

Milk fat particles are being pushed around by water molecules

Milk fat particles are being pushed around by water molecules At room temperature, atoms and molecules are in constant motion Brownian motion

Grains of sand stand still…

Grains of sand stand still… … but the individual atoms are in constant, random motion. kinetic energy: the energy of motion. temperature: a measure of the average kinetic energy of atoms or molecules.

Random motion Non random motion Random motion AFFECTS temperature Non random motion DOES NOT AFFECT temperature

Temperature is an average Some molecules have more kinetic energy than the average. Some molecules have less kinetic energy than the average. Temperature is the measure of the average kinetic energy of atoms or molecules Slower (less energy) Faster (more energy)

Temperature is an average Some molecules have more kinetic energy than the average. Some molecules have less kinetic energy than the average. Temperature is the measure of the average kinetic energy of atoms or molecules

Does everyone express temperature the same way? Some of your students might come / be familiar with a country where temperatures are measured in oC. Using oC and oF, invite students to describe how hot a summer day might be, and how cold a winter night might be.

Temperature scales

Temperature scales Water boils Water freezes How can we go back and forth between the two scales?

What temperature in Celsius is the same as 100oC?

What temperature in Celsius is the same as 100oF? Asked: Temperature in oC Given: 100oF Relationships:

What temperature in Celsius is the same as 100oF? Asked: Temperature in oC Given: 100oF Relationships: Solve: Answer: 100oF is the same temperature as 37.8oC

What is the Fahrenheit equivalent of 15oC? Asked: Temperature in oF Given: 15oC Relationships:

What is the Fahrenheit equivalent of 15oC? Asked: Temperature in oF Given: 15oC Relationships: Solve: Answer: 15oC is the same temperature as 59oF.

How can we accurately measure temperature? Hot or cold? What feels hot to one person might just be warm to another. How can we accurately measure temperature?

All thermometers are based on a physical property that changes with temperature. Thermal expansion: Mercury thermometers Alcohol thermometers Electrical sensors: Thermistor Thermocouple

The temperature probe in the Lab-Master uses a thermistor All thermometers are based on a physical property that changes with temperature. Thermal expansion: Mercury thermometers Alcohol thermometers Electrical sensors: Thermistor Thermocouple The temperature probe in the Lab-Master uses a thermistor

kinetic energy: the energy of motion. temperature: a measure of the average kinetic energy of atoms or molecules.

What happens when the temperature is really, really low? What is the lowest possible temperature? You would theoretically reach a point where atoms are no longer in motion (zero kinetic energy). This would happen at absolute zero (0 kelvin) which is introduced in the next slide. kinetic energy: the energy of motion. temperature: a measure of the average kinetic energy of atoms or molecules.

Absolute zero At absolute zero the kinetic energy is essentially zero. 3 different scales

Unit conversion We have already seen:

Unit conversion + 273 - 273

Unit conversion Convert 27oC into kelvins.

Unit conversion Convert 27oC into kelvins. Asked: Temperature in kelvin Given: 27oC Relationships:

Unit conversion Convert 27oC into kelvins. Asked: Temperature in kelvin Given: 27oC Relationships: Solve: Answer: 300 K is the same temperature as 27oC.

Three temperature scales: Molecules are in constant, random motion. This affects temperature. Three temperature scales: