1. Thermodynamics Equation

2. What is Heat?
Heat is Energy- Kinetic Energy- The motion of electrons around the nucleus of an atom.
Perception as to hot and cold defined relative to out own body temperature, i.e. object is hotter or colder than oneself
I feel hot
He is hot

3. Hotter things become longer
All(?) solids get bigger when they get hot
A 1 meter long bar heated by 1 degree gets bigger by
Steel ≈0.01 mm
Glass ≈ mm
Rails expand and may buckle on a hot summer day
Join two metals with different coefficient of thermal expansion to create a bimetallic strip (fire alarms and thermostats)

4. Thermal expansion, why? x
As an atom heats up it’s electrons spin faster.
Those atoms hit each other with more force and bounce further apart
As an object is heated it becomes less dense.
Potential energy between
two atoms

5. Thermal expansion of water
Density of ice is less than water!!!
Icebergs float!
It has to do with the hydrogen bonds in water.
As water cools below 4°C, the hydrogen bonds adjust to hold the negatively charged oxygen atoms apart.

6. Conductors and Insulators
Insulators prevent heat transfer.
Examples: A vacuum, polystyrene, fibreglass, plastic, wood, brick
Conductors transfer heat easily.
Examples of poor insulators, i.e. good conductors: Most metals, Gases, liquids

7. Temperature and scales
Temperature scales (melting & boiling of water)
Degrees Celsius (MP 0°C 100°C)
Degrees Kelvin (MP K BP K)
Degree Fahrenheit (MP 32° F BP 212°F)

8. Converting between scales
Kelvin to Celsius
K = C
C = K
Fahrenheit to Celsius
F = C x (9/5) + 32
C = (F - 32) x (5/9)

9. 1st Law of Thermodynamics
Energy can be changed from one form to another, but it cannot be created or destroyed.
The total amount of energy and matter in the universe remains constant, merely changing from one form to another.

10. Heat transfer = energy transfer
Energy measured in Joules but heat often measured in calories
One cal raises one gram of water from 14.5°C to 15.5°C
1 cal = 4.186J
Doing work on something usually makes it hot
Splash in the bath and the water will get warm!
1st law of thermodynamics heat and work are both forms of energy

11. 2nd Law of Thermodynamics
Law of Entropy
When energy transfers from one object to another some energy will always be lost to heat. No machine is 100% efficient.
What is the outcome?
While the amount of energy in the universe is constant (First Law), the quality of energy deteriorates gradually over time. How so? Usable energy is used for productivity, growth and repair. In the process, some energy is lost to heat. Thus, usable energy is permanently lost to unusable energy.

12. Specific Heat
Objects heat and cool at specific rates. Some object heat up faster than others.
This is an object specific heat.

13. How to calculate… Q = mc DT Q is energy measured in J
m is mass measured in kg
C is specific heat measured in J/gC
Temperature is measured in degrees Celcius.

14. Example
A pot with 5 kg of water rises in temperature from 4°C to 8°C. If water has a specific heat of 4.18 J/gC, how much energy was used to heat the pot of water?