Can't Win, Can't Break Even, Can't Quit — the 3 Laws of Thermodynamics
Three Laws of Thermodynamics
Three laws summarized in one unforgettable sentence
1st (Can't Win): energy is conserved, can't create it. 2nd (Can't Break Even): entropy always increases, always lose some to heat. 3rd (Can't Quit): can't reach absolute zero.
1st
Energy conserved — can't create energy
2nd
Entropy increases — can't break even
3rd
Absolute zero unreachable
Ideal Gas Law
PV = nRT
Ideal Gas Law
Pressure × Volume = moles × gas constant × Temperature
P = pressure, V = volume, n = moles, R = 8.314 J/mol·K, T = temperature in Kelvin. Compress gas → pressure rises. Heat gas → pressure or volume increases.
Heat Transfer
CCR: Conduction, Convection, Radiation — 3 heat transfer modes
Heat Transfer
Three ways heat moves — remember CCR
Conduction: direct contact (metal spoon in soup). Convection: fluid movement (boiling water). Radiation: electromagnetic waves (sun warming you). Radiation needs no medium.
C
Conduction — contact
C
Convection — fluid movement
R
Radiation — EM waves, no medium needed
Second Law
Entropy always increases in isolated systems — disorder grows
Second Law
Things move from order to disorder spontaneously — never the reverse
A shattered egg never reassembles. Ice melts in warm room but water won't freeze spontaneously. The universe trends toward maximum disorder (maximum entropy).
Carnot Efficiency
Carnot efficiency = 1 - (Tc/Th) — maximum possible efficiency of any heat engine
Carnot Efficiency
No real engine can exceed Carnot efficiency — it's the theoretical maximum
Efficiency depends only on the temperatures of the hot (Th) and cold (Tc) reservoirs in Kelvin. Higher temperature difference → higher efficiency. Real engines always fall short due to irreversibility.
Temperature Scales
Temperature scales: K = °C + 273. Absolute zero = 0 K = -273°C — molecules stop moving.
Temperature Scales
Converting between Celsius and Kelvin — and what absolute zero means
Always use Kelvin in gas law calculations. 0 K (absolute zero): minimum possible temperature, molecules have minimum kinetic energy. Room temperature ≈ 293 K. Water freezes at 273 K, boils at 373 K. Fahrenheit: °F = (9/5)°C + 32.
Specific Heat Capacity
Specific heat capacity: Q = mcΔT. Water has high specific heat — resists temperature change.
Specific Heat Capacity
How much energy is needed to change a substance's temperature
Q = heat energy (J), m = mass (kg), c = specific heat capacity (J/kg·K), ΔT = temperature change. Water: c = 4,186 J/kg·K — very high. Metals: much lower c. High specific heat = more energy needed to heat up = slower temperature change. This is why coastal cities have milder climates.
Thermal Expansion
Thermal expansion: solids, liquids, and gases all expand when heated. Bridges have expansion joints.
Thermal Expansion
Most materials expand when heated and contract when cooled
Linear expansion: ΔL = αLΔT where α = coefficient of linear expansion. Volume expansion: ΔV = βVΔT where β ≈ 3α. Applications: gaps in railroad tracks and bridges (expansion joints), thermostats (bimetallic strips), thermometers. Exception: water expands when it freezes (ice less dense than water).
Heat Engines
Heat engines: take heat from hot reservoir, do work, dump waste heat to cold reservoir
Heat Engines
How all heat engines work — from car engines to power plants
All heat engines follow the same principle: absorb heat Qh from hot source, convert some to work W, reject remaining heat Qc to cold sink. Efficiency = W/Qh = 1 - Qc/Qh. Carnot efficiency is the theoretical maximum: 1 - Tc/Th. Real engines always less efficient due to friction and irreversibility.
Phase Changes
Phase changes: melting, freezing, vaporization, condensation, sublimation. Temperature constant during phase change.
Phase Changes
What happens to temperature during a change of state
During a phase change, temperature stays constant while energy goes into breaking/forming intermolecular bonds. Latent heat of fusion (melting/freezing): energy to change between solid and liquid. Latent heat of vaporization: energy to change between liquid and gas. Q = mL where L = latent heat.
Zeroth Law
Zeroth Law of Thermodynamics: if A=B in temperature and B=C, then A=C. Basis of thermometers.
Zeroth Law
The law that makes temperature measurement possible
If object A is in thermal equilibrium with object B, and object B is in thermal equilibrium with object C, then A and C are in thermal equilibrium with each other. This is why thermometers work — they reach equilibrium with whatever they measure. Called 'zeroth' because it was defined after 1st and 2nd laws.
Q/t = kAΔT/d. k = thermal conductivity (high k = good conductor, low k = good insulator). A = cross-sectional area. ΔT = temperature difference. d = thickness. Metals have high k. Air, wood, foam have low k. R-value (insulation): R = d/k, higher R = better insulator.