Heat

1
Heat

• c specific heat capacity

2
Specific heat capacity of Liquid water

• Liquid water has a high specific heat capacity

3
Specific heat capacity

• Wood coals have a low specific heat capacity
• Ash is a poor conductor of heat
• Keep moving

4
Specific heat capacity
5
Heat of fusion

• Amount of energy required to melt or freeze a
  substance

6
Heat of vaporization

• The amount of heat required to boil a liquid that
  is already at the boiling temperature

7
How much heat is needed in order to change the
temperature of a 10 gram ice cube that is at
-30C, to a vapor at 140C?
Step 1
8
How much heat is needed in order to change the
temperature of a 10 gram ice cube that is at
-30C, to a vapor at 140C?
melt
0C
0C
Step 2

• Notice that the heat only melted the ice and that
  the temperature remains constant

9
How much heat is needed in order to change the
temperature of a 10 gram ice cube that is at
-30C, to a vapor at 140C?
warm
Step 3
0C
100 C

• Use this warming equation, every time there is
  a temperature change

10
How much heat is needed in order to change the
temperature of a 10 gram ice cube that is at
-30C, to a vapor at 140C?
Step 4
Boil
100C
100C

• Notice that in this step, the heat only changes
  the state of the water, not its temperature

11
How much heat is needed in order to change the
temperature of a 10 gram ice cube that is at
-30C, to a vapor at 140C?
Step 5
warm

• Another place where the temperature does change

12
How much heat is needed in order to change the
temperature of a 10 gram ice cube that is at
-30C, to a vapor at 140C?
150 calories 800 calories 1000 calories
5400 calories 200 calories 7550 calories
Step 6

• The total energy required will be 7,550 calories

13
The energy that powers storms, comes from the
sun. The energy is stored in water when it
evaporates from the ocean.
Katrina 2005
14
Why is it dangerous to open the radiator cap when
the engine is hot?

• The water in the cars cooling system is
  pressurized. Its temperature is well above the
  normal boil point of water.
• When the cap is opened, the pressure is reduced
  and much of the water vaporizes-causing an
  explosion.

15
1st law of thermodynamics A conservation of
energy statement

• ?U change in internal energy
• W work
• Q heat

16
1st law of thermodynamics A conservation of
energy statement

• If heat flows into a system, and no work is done,
  its internal energy must increase.
• If heat flow out of a system, and no work is
  done, its internal energy must decrease.

17
1st law of thermodynamics A conservation of
energy statement

• If the gas does work, it must lose energy.

18
How does a gas do work?

• As it expands, it pushes surrounding air away.

• Work done an the expanding gas, equals its
  pressure times the change in its volume.

19
What does or - W mean?

• If work is done to a gas, its internal energy
  must increase. It must gain energy.
• - If work is done by the gas, its internal energy
  must decrease. It must lose energy.

20
Adiabatic cooing

• When a warm air mass rises, it will be surrounded
  by air of less pressure. Therefore the rising
  air expands, does work and cools down.

21
Adiabatic warming

• As a cold air mass sinks, it is surrounded by air
  of higher pressure. The sinking air mass is
  compressed-work is done to it.
• The sinking air mass gains energy and warms up.

22
The secret behind refrigeration

• A gas is pressurized into a liquid by a
  refrigerator motor-compressor. It warms up and
  is radiated away into the kitchen.
• The liquid is then sent to a larger diameter tube
  and expands into a gas.
• The expanding gas does work and must therefore
  lose energy.
• The cold gas is in the tubes that are in the
  refrigeration unit.
• The gas goes back to the compressor and the cycle
  starts again.

23
The second law of thermodynamics

• Left to itself, the natural tendency of a system
  is for its entropy to increase.
• Entropy is a measure of a systems disorder.