Thermodynamics Section Three - The Language of Thermodynamics

what form can energy exchange take

heat or work

what is a system

a volume of space containing matter and energy that we have chosen for analysis. It is separated from the rest of the world by a boundary

what is a boundary

across which the system may or may not exchange matter and energy

what is an isolated system

no exchanges of any kind

what is a closed system

only energy exchange

what is an open system

both energy and mass exchange

what is a rigid system

a closed system not exchanging mechanical work

what are the state variables of pure fluids

pressure volume and temperature

what is a state function

a function of the state variable

what is the equation of state for an ideal gas

PV = nRT

what is R

Gas constant : 8.314JK-1mol-1

what is avogadro’s number

one mole = 6.023 × 10^(23) = NA

what is atomic weight

the mass of one mole of the substance in grammes with units gmol^-1

what is an intensive state variable

independent of the systems mass

example of intensive variables

T,P

what is an extensive state variable

proportional to the systems mass

example of extensive variable

n, V

what is a thermodynamic reservoir

an infinite system whose properties remain unchanged when brough into contact with any finite system

when isa system in thermal equilibrium

if its intensive properties are uniform and dont change with time - the temperature and pressure will take the values of the reservoir

what is a reversible process

taking a system from one state to another by following a path along which every intermediate is an equilibrium state

how do we ensure every step is an equilibrium state

no temperature of pressure gradients which render the system inhomogeneous

how to we allow change while having no gradients

allow infinitesimal gradients to give the process a direction

what does dt<0 mean

energy flows from hot to cold

what does dP<0 mean

volume flows from low to high pressure

what is a quasistatic process

only infinitesimal pressure and temperature exist so that the process is sufficiently slow to allow the system to come fully to equilibrium at every stage

how is a reversible process achieved

by a quasi static process that is also frictionless

how does changing sign of dT and dP affect process

it reverses it

what is a cyclic process

returns to the same state at the end

what is requirement for cyclic process

integral of dX =0 where X is a state variable