Second law: entropy and spontaneity
Chemical Thermodynamics · Chemistry
Gas piston lab
Interactive 3DHeat the gas and watch molecules speed up — pressure obeys the gas laws live.
Controls
Drag the sliders or type a value — the simulation updates live.
K
200K600K
×
0.5×2×
Study notes
Ice melts at 25°C (ΔH_fus = +6.0 kJ/mol). Show it's spontaneous via entropy. Step 1: ΔS_sys = ΔH/T = 6000/298 = +20.1 J/K·mol (disorder rises). Step 2: ΔS_surr = −ΔH/T = −6000/298 = −20.1 J/K·mol... at 0°C exactly. Step 3: At 25°C surroundings are warmer: heat flows from warm room, |ΔS_surr| < ΔS_sys. Step 4: ΔS_univ = +20.1 − 6000/298... net positive → spontaneous ✓. Below 0°C the balance flips — ice stays frozen.