Thermodynamics Flashcards
temperature
measure of the average kinetic energy of the molecules of a substance
heat
energy transferred across system boundary due to a temperature difference between system and surroundings
thermal equilibrium
two objects will not exchange energy by heat or electromagnetic radiation if placed in thermal contact
heat capacity
amount of energy needed to raise temperature by 1oC
specific heat
heat capacity per unit mass
latent heat of fusion
phase change from solid to liquid
latent heat of vaporisation
phase change from liquid to gas
Zeroth Law of Thermodynamics
If objects A and B are in thermal equilibrium with a third object C, then A and B are in thermal equilibrium with each other
convection
movement of material in liquids and gases
conduction
solids: contact between hot and cold regions
radiation
no contact: energy transferred from hot to cold through electromagnetic waves
ideal absorber
object that absorbs all energy incident on it - black body - also ideal radiator
ideal reflector
absorbs none of the energy incident on it
Adiabatic Process
no heat transfer between system and surroundings
Isovolumetric Process
constant volume - no work done
Isothermal Process
constant temperature - no change in internal energy
Isobaric Process
constant pressure
Cyclic Process
start and end in same state - no change in internal energy
Entropy
measure of disorder - state variable, independent of path taken - which direction a process should go
Second Law of Thermodynamics
process in a closed system: entropy increases for irreversible processes, remains constant for reversible - S>=0
Reversible process
no dissipative effects or energy losses - every point along some path is an equilibrium state: system can be returned to original state along same path
Irreversible process
all natural processes
Heat Death of the Universe
entropy of universe will be maximised - all processes will cease
Heat Engine
carries some substance through a cyclic process, during which the working substance absorbs energy by heat from a high temp. reservoir, work is done by the engine, energy expelled by heat to a lower temp. reservoir
Carnot Cycle
heat engine operating in ideal, reversible cycle: most efficient engine possible
Carnot’s Theorem
no engine can be more efficient than a Carnot engine operating between the same two reservoirs
