1. Ch 15: laws of Thermo
Includes ideas about energy and work associated with a working gas in a piston/cylinder arrangement

2. Law of Conservation of energy
Change in U (internal energy) = Q + W.
Q = amount of heat added so this is positive when heat added and negative when heat leaves the gas.
W = Work done on the gas. If the gas expands, work done by the gas is negative. If work is done on the gas (the gas contracts), then W is positive (the internal energy U goes up).
Work is done only when gas expands or contracts.
Work is done only when the VOLUME CHANGES!

3. Volume contracting: work done on the gas
When gas is compressed work done on the gas is positive.

4. Transfer of energy into a gas
Energy can be transferred in 2 ways.
Work (W) can be done: the gas either contracts (W = + on the gas) or expands (W = - on the gas)
Heat (Q) can be transferred into or out of the gas.
If the internal energy of the gas changes, the temperature must also change (U = 3/2kT)

5. Work done BY a gas
Work = force x distance , Force = P x area, and area x distance = volume, so Work = P x change in Volume.
W = P (Vf –Vi) (for constant pressure process)
W = area under the PV diagram.
Work is positive if the gas contracts, negative if the gas expands.
The amount of work depends on how you get from the initial to the final states.

6. Isothermal process= constant temp 15-2
If the temperature does not change, then internal energy (U) also does not change, so Q = W
Work done on the gas = heat exchanged.

7. Types of processes
Cyclic process: process returns to its original state after the cycle. Therefore, the internal energy U doesn’t change. Then Q = W.
Adiabatic: No heat is transferred so Q = 0. This yields change in U = W.
Isobaric = process at constant pressure where the work done is then W = P(Vf-Vi)

8. Work during constant pressure (adiabatic) process
Work = area under PV diagram

9. Constant Volume process
No Work done if Volume does not change. So U = Q

10. Isothermal process
If gas allowed to expand as constant temperature, then change in U = 0 ,
So Q + W = 0