Key Terms
Critical property
U depends only on the STATE of the system, not the path taken to get there. Pressure, volume, and temperature determine
ISOBARIC (constant pressure)
W = P * delta-V Work equals pressure times change in volume. On a PV diagram, this is a horizontal line; work = area und
ISOCHORIC (constant volume)
Delta-V = 0, so W = 0. No work done.
ISOTHERMAL (constant temperature)
For an ideal gas, delta-U = 0 when T is constant; so Q = W. Whatever heat enters must equal the work done by the gas.
ADIABATIC (no heat transfer)
Q = 0, so delta-U = -W. When a gas expands adiabatically, it does work at the expense of internal energy; temperature dr
Reversible process
Both system AND environment can return to original states by following the reverse path. Requires no friction, turbulenc
PV diagram
Isothermal expansion AB at T_h; adiabatic expansion BC; isothermal compression CD at T_c; adiabatic compression DA back
CRITICAL
T_c and T_h must be in KELVIN (absolute temperature scale).
Restated second law
A Carnot engine operating between two temperatures has the greatest possible efficiency of any engine operating between
Real refrigerators and AC units
COP typically 2 to 6. Real heat pumps: COP typically 2 to 4.
Example
4000 J transferred from 600 K reservoir to 250 K reservoir before reaching a Carnot engine produces 933 J less work than
Melting ice
Solid water (ordered crystal structure) becomes liquid (disordered). Large entropy increase.
Macrostate
Overall description of a system (total heads and tails, total pressure and temperature); does not specify individual det
Microstate
Complete detailed description of every element (which specific coins are heads or tails, exact positions and velocities
First Law
Delta-U = Q - W Isobaric work: W = P * delta-V Heat engine efficiency: Eff = W / Q_h = 1 - (Q_c / Q_h)