P-V Diagrams and processesContents:• Basic Concept• Example• Whiteboards

P-V diagrams

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The axesChange volume?Change pressure?

Volume

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eIsobaric Expansion (+W)

Isobaric Compression (-W)

Iso = samebaric = pressure

P-V diagrams

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Volume

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Isochoric = same volume(closed container)how does it happen?

Adiabatic (no heat flow) processes

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Volume

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Adiabatic expansion: (Q = 0)Work is done by the gas (+W)No heat flows in: Q = U + W0 = U + W, U = -WInternal energy (T) drops

ExamplesAir rocketsCold side of fridgeUniverseDemo - cloud

Adiabatic (no heat flow) processes

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Volume

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e

Adiabatic compression: (Q = 0)Work is done on the gas (-W)No heat flows in: Q = U + W0 = U + W, U = -(-W)Internal energy (T) rises

ExamplesBike pump/dieselsHot side of fridgeCompressorsDemo – plunger/Murray Frig

Isothermal (constant temperature) processes

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Volume

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Isothermal expansion: (T = 0)Work is done by the gas (+W)Internal energy is constant (U = 0)Q = U + W = W Heat turns to work (slowly)

Isothermal (constant temperature) processes

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Volume

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Isothermal compression: (T = 0)Work is done on the gas (-W)Internal energy is constant (U = 0)Q = U + W = W Work turns to heat (slowly)

What’s goin’ on here?

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Volume

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isobaric expansionheat flows in, temp increases

What’s goin’ on here?

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Volume

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isochoric coolingheat flows out, pressure drops

What’s goin’ on here?

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Volume

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isochoric heating, isobaric expansion

Which process is adiabatic, which is isothermal?

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Volume

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In which process would the temperature drop?B is adiabatic

A

B

Which process is adiabatic, which is isothermal?

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Volume

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In which process would the temperature increase?B is adiabatic

A

B

A complete cycle:

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Volume

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Complete cycle - where is work done?Is more work done by gas or on the gas?

A

B C

D