1. Temperature, Heat, and Expansion
Chapter 21

2. Temperature
Temperature – the quantity that tells how hot or cold something is compared with a standard
A common thermometer measures temperature by showing the expansion and contraction of a liquid in a glass tube using a scale
Celsius Scale – most widely used temperature scale, 0ºC is the point at which water freezes and 100ºC the point at which water boils, the gap between is divided into 100 equal parts

3. Temperature
Fahrenheit Scale – commonly used in the U.S., has 180ºF between freezing and boiling (32ºF and 212º)
Kelvin Scale – used in scientific research, degrees are the same size as Celsius + 273º, denoted K
Absolute Zero – the lowest possible temperature on the Kelvin scale, substance has no kinetic energy

4. Thermometers

5. Scale Comparison

6. Temperature and Kinetic Energy
In an ideal gas, temperature is proportional to the average kinetic energy
The heat that you feel when you touch a hot surface is the kinetic energy transferred by molecules in the surface to molecules in your fingers
Temperature is not a measure of the total kinetic energy

7. Heat
Heat – the energy that transfers from one object to another because of a temperature difference between them
Matter does not contain heat, but contains energy in several forms
Heat is energy in transit
Internal Energy – the energy resulting from heat flow
When heat flows from one object or substance to another it is in contact with, the objects are said to be in thermal contact
Heat flows from the higher-temperature substance into the lower-temperature substance

8. Heat Flow Between Two Gases

9. Thermal Equilibrium
Thermal Equilibrium – objects in thermal contact with each other reach the same temperature, no heat flows between them
When reading a thermometer, we wait until the thermometer has reached thermal equilibrium with the object we want the temperature of

10. Thermal Equilibrium

11. Internal Energy
Internal Energy – the total of all energies inside a substance
A substance does not contain heat – it contains internal energy
When a substance takes in or gives off heat, any of these energies can change

12. Internal Energy

13. Measurement of Heat
To quantify heat, we have to specify the mass and kind of substance affected
Calorie – the most commonly used unit for heat; the amount of heat required to raise the temperature of 1 gram of water by 1ºC
Kilocalorie – the heat required to raise 1 kilogram of water by 1ºC (1000 calories)
The heat unit for rating foods is actually the kilocalorie (to distinguish from calorie, it is often written as Calorie)
Remember that a calorie is a measure of ENERGY!
The relationship between calories and joules is:
1 calorie = Joules

14. Calories

15. Specific Heat Capacity
Different substances have different capacities for storing internal energy
We find that specific materials require specific quantities of heat to raise the temperature of a given mass of the material by a specified number of degrees
Specific Heat Capacity – the quantity of heat required to raise the temperature of a unit mass of a substance by 1ºC
Q = mcΔT
Q = quantity of heat; m = mass of substance;
c = specific heat capacity of substance;
ΔT = change in temperature
We can think of specific heat capacity as thermal inertia (an object’s resistance to change)

16. Specific Heat Capacities

17. Thermal Expansion
When the temperature of a substance increases, the molecules “jiggle” faster and move further apart, causing an expansion of the substance
Gases generally expand and contract more than liquids, which expand and contract more than solids
In concrete sidewalks and highways this expansion and contraction is taken into account when it is being built. The surface is laid down in small sections with a gap in between, that is usually filled with a substance such as tar.

18. Thermal Expansion
Expansion Joint

19. Expansion of Water
Almost all liquids will expand when they are heated, ice-cold water instead contracts to go from ice to a liquid
When the water reaches a temperature of 4ºC, it will stop contracting and begin expanding
This has to do with the crystal structure of water, its solid state has an open structure that takes up more volume and is therefore less dense

20. Expansion of Water

21. Assignment – Due Tuesday 1/22
Read Chapter 21 (pg )
Do Chapter 21 #19-39 (pg )