1. SPH3U: Energy, Work, Power
Temperature & Heat

2. Molecules and Thermal Energy
The kinetic molecular theory of matter states that matter is made up of particles (molecules, atoms, ions) that are in constant random motion. These particles are continually vibrating, rotating, and colliding with one another.

3. Molecules and Thermal Energy
The particles that make up matter have kinetic energy because of their constant motion. As particles vibrate, their energy constantly alternates between kinetic energy and elastic potential energy. Particles also have potential energy due to the forces of attraction or chemical bonds between them.

4. Molecules and Thermal Energy
Thermal energy is the total kinetic and potential energy of the particles within an object. Thermal energy is internal energy – the energy associated with the movement and interactions of the particles. An object has thermal energy in addition to any potential energy or kinetic energy it may have as a whole.
For example, a car moving over a bridge has kinetic energy because it is moving, Gravitational potential energy because it is high on the bridge, and thermal energy because of the particles that make up the car.

5. Temperature
As particles move, they collide, and when they do, they transfer kinetic energy back and forth among themselves. In this way, energy can be transferred from one part of an object to another, or even from one object to another object.

6. Temperature
The temperature of a substance is the average kinetic energy of the particles. The greater the average kinetic energy of the particles, the higher the object’s temperature.
Temperature is measured in either Celsius or Kelvin. The standard SI unit is the Kelvin (K).
0 C = 273 K

7. Temperature
Absolute zero is the lowest temperature that is theoretically possible. It occurs at a temperature of 0 Kelvin, or -273C. At absolute zero, molecular motion and energy would be minimal.

8. Heat
Heat is the energy transferred from a warmer object to a cooler one.
Example: When we place hot chocolate in a mug, the particles in the hot chocolate have a lot of kinetic energy because they are hot. They will in turn collide with particles in the mug, and transfer some of their energy to the particles in the mug through these collisions. As a result, over time, the hot chocolate loses heat and the mug gains heat.

9. Heat
Heat is always transferred from a hotter object to a colder object. If two objects are the same temperature, there will be no heat transfer.

10. Heat
However, when two contacting surfaces are rubbed against one another, friction exists as the particles in the substance to move past each other and their kinetic energy gets transferred into thermal energy, causing a rise in temperature. You can see this when your rub your hands together – they get warm.
The conversion of kinetic energy to thermal energy by friction is why no mechanical process can be 100% efficient.

11. Ways to transfer Thermal Energy
Conduction
The transfer of thermal energy through direct contact of substances. Example: hot chocolate in a mug

12. Ways to transfer Thermal Energy
Convection
The transfer of thermal energy through the bulk movement of particles from one location to another. This occurs in liquids and gases. Convection is a natural stirring of a fluid: hotter, less dense material flows up while cooler, denser material flows down. Eventually all the material is heated to a uniform temperature. Example: boiling water.

13. Ways to transfer Thermal Energy
Radiation
Radiation is the transfer of thermal energy through fast moving particles or electromagnetic waves. Example: heat given off by the sun

14. Heat Capacity
Materials are affected by thermal energy differently. Heat capacity (c) is the amount of thermal energy needed to change the temperature of an object or system by 1 Kelvin, or 1C.
You need a different amount of thermal energy to raise the temperature of water by 1 Kelvin than you would to heat milk by 1 Kelvin. In fact, it takes 4190 Joules of energy to raise the temperature of 1 kg of water by 1 Kelvin, where as it takes 3930 Joules to raise the temperature of 1 kg of milk by 1 Kelvin.

15. Heat Capacity
The amount of thermal energy (Q) you need to heat an object depends on three things:
The mass of the object
How much temperature change you are trying to get
The type of material (specific heat capacity)

16. Heat Capacity
The following formula is used to relate these four things:
Q = mcΔT.
(Q = thermal energy, m = mass, c = specific heat capacity,and ΔT = temperature change)

17. Example 1
A 515-g granite rock cools from 450C to 100C. The specific heat capacity of granite is Calculate how much thermal energy is lost by the rock.

18. Example 1
A 515-g granite rock cools from 450C to 100C. The specific heat capacity of granite is 790 J/kgK. Calculate how much thermal energy is lost by the rock.
ΔT = 350 K
m = kg
c = 790 J/kgK
Q = mc ΔT
Q = (0.515)(790)(350)
Q = J
Therefore the total amount of thermal energy lost by the rock is approximately Joules.

19. The Principle of Heat Exchange
When two substances at different temperatures are mixed, the amount of thermal energy lost by the hotter substance in cooling is equal to the amount of thermal energy gained by the colder substance in warming.

20. The Principle of Heat Exchange
The thermal energy gained by the cooler substance equals the thermal energy lost by the warmer substance.
If you mix together two substances that are at initial temperatures T1 and T2, you can use the principle of heat exchange to predict the final temperature, Tf.
Q1 + Q2 = 0
m1c1(ΔT1) + m2c2(ΔT2)=0
m1c1(Tf - T1) + m2c2(Tf – T2 )=0

21. Example 2
An insulated cup containing 255 grams of water at 21.6C is emptied into another insulated cup containing 407 grams of water at 63.8C. Determine the final temperature of the mixture, assuming that no thermal energy is lost.

22. Example 2 - Solution Q1 + Q2 = 0 m1c1(ΔT1) + m2c2(ΔT2)=0
m1c1(Tf - T1) + m2c2(Tf – T2 )=0
m1c(Tf - T1) + m2c2(Tf – T2 )=0
c [m1 (Tf - T1) + m2(Tf – T2 ) ]=0
(0.255) (Tf – 21.6) + (0.407)(Tf – 63.8) =0
0.255Tf – Tf = 0
Tf – = 0
Tf = 47.5 C
m1 = kg
m2 = kg
c1 = c2 = c
T1 = 21.6C
T2 = 63.8C

23. Homework – Extra Practice
Attempt the homework questions on the handout
Pg. 287 # 1-6