B4 Thermodynamics - Key terms

device that uses the flow of thermal energy to do useful work

branch of physics involving transfers of thermal energy to do useful work

allows the free flow of thermal energy, but not matter

part of the surroundings of a thermodynamic system that is kept at approximately constant temperature and is used to encourage the flow of thermal energy

occuring at constant pressure, ΔP = 0

work is done by a gas when it expands (W is positive), work is done on a gas when it is compressed (W is negative), at constant pressure W=PΔV, if the pressure changes then the work done can be determined from the area under a PV diagram

specified by quoting the pressure, P, temperature, T, and volume, V, of a known amount, n, of gas

if an amount of thermal energy +Q, is transferred into a system, then the system will gain internal energy, +ΔU, and/or the system will expand and do work on the surroundings, +W: Q=ΔU + W

occurring at constant volume

occurring without thermal energy being transferred into or out of a thermodynamic closed system

the substance (usually a gas) used in thermodynamic processes to do useful work

a series of thermodynamic processes that return a system to its original state (for example, the Carnot cycle), usually the process repeats continuously

the most efficient thermodynamic cycle, an isothermal expansion followed by an adiabatic expansion; the gas then returns to its original state by isothermal and adiabatic compressions

device which transfers thermal energy from a colder place by doing work

a process which cannot be reversed, and in which entropy (see below) always increases, all real macroscopic processes are irreversible

a process that can be reversed so that the system and all of its surroundings return to their original states and there is no change in entropy, an impossibility in the macroscopic world

the way in which particles are arranged, or energy is distributed, can be described in terms of the extent of patterns and similarities

a measure of the disorder of a thermodynamic system of particles

the overall entropy of the universe is always increasing, this implies that energy cannot spontaneously transfer from a palce at low temperature to a place at high temperature, or, in the Kelvin version: when extracting energy from a heat reservoir, it is impossible to convert it all into work

the numerous possible combinations of microscopic properties of a thermodynamic system

when an amount of thermal energy, ΔQ, is added to or removed from a system at temperature T, the change in entropy, ΔS, can be calculated from the equation ΔS = ΔQ/T