B4 Thermodynamics

typical thermodynamic system

consists of a fixed mass of gas separated from its surroundings by a rigid cylinder and moveable piston

heat

energy that flows by conduction, convection or radiation from one body to another due to temperature different between them

work

energy that is transferred from one system to another by a force moving its point of application in its own direction

internal energy

the total disordered energy of all the particles of the body

zeroth law of thermodynamics

when a hot body is placed in contact with a colder body, heat flows from the hot one to the cold one until bodies are in thermal equilibrium

first law of thermodynamics

the conversion of heat to work (and vice versa) in a thermodynamics system (energy conservation)

heat supplied (Q)

positive - heat flow into gas

negative - heat flow out of gas

internal energy (U)

positive - increase in internal energy of gas

negative - decrease in internal energy of gas

work done (W)

positive - work done by gas to surroundings (expand)

negative - work done by surroundings to gas (compress)

isobaric process

constant pressure

∆P=0

isochoric/isovolumetric process

constant volume

∆V=0, W=0

Q=∆U

isothermal process

occurs slowly

follows Boyle’s law

∆T=0, ∆U=0

adiabatic process

occurs rapidly so no time for heat exchange and moves between isotherms

• compression work on gas - increases internal energy and temperature

• expansion work by gas - decreases internal energy and temperature

Carnot cycle

(A) isothermal expansion —> (B) adiabatic expansion —> (C) isothermal compression —> (D) isothermal compression

entropy

measure of disorder/randomness of a system

high entropy

• greater number of possible speeds and positions for the particles to be in

• lower probability of particles being in any particular state

• an increase in volume increases the amount of positions particles can be in

second law of thermodynamics

when a heat engine converts heat into work, some energy is lost to the surroundings (i.e. never 100% efficiency)