Pressure and Temperature are

directly proportional as long as the

temperature is measured in Kelvins

Pressure Law

Boyle’s Law

Each line represents an experiment done at a different temperature

PistonsWork Done = Force x Change of Distance

Wd = F . Δd

but

Wd = P.A.Δd

Wd = P. ΔV

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

𝑄=∆𝑈+𝑊First 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 lost2. Internal Energy can rise or fall3. Work can be done ‘on the gas’ or ‘by the gas’

1. Isobaric

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

ConstantPressure

2. Isovolumetric / Isochoric

1. The gas isn’t expanding or contracting. No Work is done. ΔW=02. Because the Pressure is increasing the temperature must be

rising so ΔU is +ve3. Q = ΔU + W so Q = ΔU so heat is +ve4. Heat must have been added

ConstantVolume

3. Isothermic

1. The gas is expanding – doing Work (Work is +ve)2. The temperature is constant so ΔU is 03. Q = ΔU + W so Q =W4. Heat must have been added to enable the gas to do work

ConstantTemperature

4. Adiabatic

1. No heat is exchanged so Q = 02. 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

No Heat is being exchanged –

perfectly insulated.

Adiabatic lines are always steeper than Isotherms

A Heat CycleA-BIsochoric / Isovolumetric Temperature rise

B-CIsobaric Expansion

C-DIsochoric / IsovolumetricTemperature drop

D-AIsobaric Contraction

The Carnot Cycle

Forward Carnot Cycle

D

Reverse Carnot Cycle