Thermodynamics

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# Thermodynamics - PowerPoint PPT Presentation

Thermodynamics. The study of heat in motion. thermodynamic process - one in which heat is added to or taken away from a system. internal energy ( U) - defined by the system’s temperature, volume, and pressure.

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## PowerPoint Slideshow about 'Thermodynamics' - jess

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Presentation Transcript

### Thermodynamics

The study of heat in motion.

thermodynamic process- one in which heat is added to or taken away from a system.

• internal energy(U)- defined by the system’s temperature, volume, and pressure.
• first law of thermodynamics – the change in the internal energy of the system is equal to the sum of the heat added and the work done on the system.
• second law of thermodynamics - heat will never flow from a cold object to a hot object, but only from a hot object to a cold object.
Definitions

ΔU = Q + W

• U is the change in internal energy of the system, Q is the heat added to the system, and W is the work added to the system (or done on the system).
• Qis positive when it is added to the system and negative if it is taken out of the system.
• Wis positive if it is added to the system and negative if it is done by the system. This means that the work done by an engine that uses heat is negative. Think of it as being negative because it is leaving the system.
• output work is negative
• input work is positive
First Law of Thermodynamics:

Isobaric – the pressure stays the same

W = PΔV

• Adiabatic – there is no net heat transfer

ΔU = W

• Isothermal – no change in temperature

Q = -W

• Isochoric – the volume stays constant

ΔU = Q

Thermodynamic Processes
• ΔQ = 0 ΔU = Q + W ΔU = W
• Two scenarios:
• The system is insulated so that heat can neither enter nor leave.
• The process happens so fast that there is no time for heat to be transferred.
• The following can happen:
• A gas that is adiabatically expanded will lose internal energy (ΔU) and become warmer.
• A gas that is adiabatically compressed will gain (ΔU) and become cooler.

ΔU = Q + W

0 = Q + W

Q = -W

Isothermal Processes

W = PΔV = P(0) = 0

ΔU = Q + W ΔU = Q + 0 ΔU = Q

Example: Pressure Cooker

Isochoric Processes

Heat engines operate by converting heat into work.

• Heat is added to the engine at a high temperature. Part of the heat is used to generate work and the rest of the heat is sent to some low temperature environment.
Heat Engines

Isothermal Expansion