1. Pressure Law
Pressure and
Temperature are
directly proportional
as long as the
temperature is
measured in Kelvins

2. Boyle’s Law
Each line represents an experiment done at a
different temperature

4. Pistons
Wd = P.A.Δd
Wd = P. ΔV

5. Wd = P. ΔV
As long as there is an AREA under the line then
you can see that work is done (and calculate it)

6. First Law of Thermodynamics
It just says that if you add Heat to a gas it must be
equal to the Work Done by the gas + any change in
Internal Energy
This is mainly difficult because:
1. Heat can be gained or lost
2. Internal Energy can rise or fall
3. Work can be done ‘on the gas’ or ‘by the gas’

7. 1. Isobaric
Constant
Pressure
1. The gas is expanding – doing Work (Work is +ve)
2. The temperature is increasing so ΔU is increasing (ΔU is +ve)
3. ΔQ = ΔU + W so Q must be +ve
4. Heat must have been added

8. 2. Isovolumetric / Isochoric
Constant
Volume
1. The gas isn’t expanding or contracting. No Work is done. ΔW=0
2. Because the Pressure is increasing the temperature must be
rising so ΔU is +ve
3. Q = ΔU + W so Q = ΔU so heat is +ve
4. Heat must have been added

9. 3. Isothermic
Constant
Temperature
1. The gas is expanding – doing Work (Work is +ve)
2. The temperature is constant so ΔU is 0
3. Q = ΔU + W so Q =W
4. Heat must have been added to enable the gas to do work

10. 4. Adiabatic
No Heat is being
exchanged –
perfectly
insulated.
1. No heat is exchanged so Q = 0
2. Volume is reducing so Work is being done ON THE GAS (W= -ve)
3. Q = ΔU + W so 0 = ΔU - W
4. ΔU = W so work done on the gas increases the Internal energy of
the gas
Adiabatic lines are always steeper than Isotherms

11. A Heat Cycle
A-B
Isochoric / Isovolumetric
Temperature rise
B-C
Isobaric Expansion
C-D
Isochoric / Isovolumetric
Temperature drop
D-A
Isobaric Contraction

13. The Carnot Cycle

14. Forward Carnot Cycle

15. Reverse Carnot Cycle
D