Heat

1. Heat

2. Heat • Temperature and heat are not the same thing • We measure how hot or cold something is by temperature • There are three common scales to measure temperature

3. Heat • The scale we are the most familiar with is the Fahrenheit scale • Water freezes at 32 degrees Fahrenheit • Water boils at 212 degrees Fahrenheit

4. Heat • Another temperature scale is the Celsius temperature scale • Water freezes at 0 degrees Celsius • Water boils at 100 degrees Celsius

5. Heat • The temperature scale that scientists use is the Kelvin scale • Water freezes at 273.15 Kelvin • Water boils at 373.15 Kelvin • Kelvin is the SI unit for temperature

6. Heat • To convert from Kelvin to Celsius simply subtract 273.15 • To convert from Celsius to Kelvin simply add 273.15 • All temperatures must be in Kelvin unless you are taking the change in temperature, then Celsius is okay, since a degree is the same increment for both

7. Heat • To convert from Fahrenheit to Celsius • °C = (5/9)(°F - 32) • To convert from Celsius to Fahrenheit • °F = (9/5)°C + 32

8. Heat • Temperature is a measure of the average kinetic energy (KE) an object contains • Heat is what we call a transfer of energy from one object to another • Energy always flows from a warmer object to a colder one

9. Heat • A warmer object will continue to transfer energy to a colder one until equilibrium is reached • The warmer object always gives up energy to a colder one • Scientists prefer to call heat internal energy

10. Heat • Different substances absorb heat (energy) at different rates • The rate at which this substance absorbs heat is called it specific heat capacity • There is an equation to determine how much energy is absorbed

11. Heat • Q = mCΔT • Q - the amount of energy (measured in Joules) • m - the mass of the substance (measured in kilograms) • C - the specific heat capacity (measured in Joules per kilogram Kelvin

12. Heat • ΔT - the change in temperature (measured in Kelvin or Celsius) • Again we can use Kelvin or Celsius since we are taking the difference in temperature

13. Heat • Water has a very high specific capacity which gives water its unique properties • It can absorb a tremendous amount of energy without a significant temperature change

14. Heat • The high specific heat of water is why coastal areas don’t vary in temperature too much • The large amount of water on Earth keeps us from having drastic temperature changes between day and night and summer and winter

15. Heat • Water can absorb 4180 J of energy per kilogram and only increase temperature by one degree • Water can also release 4180 J of energy per kilogram and only decrease temperature by one degree

16. Heat • Example 1: • How much thermal energy does it take to change 2 kg of water from room temperature (20°C) to boiling (100°C)?