Thermodynamics - ChemHub

01 First Law - Conservation of Energy

Energy cannot be created or destroyed, only converted. The internal energy of the universe is constant. In chemistry: ΔU = q + w (change in internal energy = heat added + work done on the system). Enthalpy (H) measures heat flow at constant pressure - the chemist's version of energy for most lab reactions.

02 Second Law - Entropy

The total entropy (disorder) of the universe always increases in a spontaneous process. Entropy is why ice melts, perfume spreads, and dropped glasses shatter but shattered glasses don't reassemble. Gibbs Free Energy: ΔG = ΔH - TΔS. A reaction is spontaneous when ΔG < 0.

03 Third Law & Absolute Zero

At absolute zero (0 K, -273.15°C), the entropy of a perfect crystal is zero. Absolute zero is the coldest possible temperature - you cannot reach it, only approach it. Current record: 38 picokelvins, achieved at MIT in 2003.

04 Key Facts

→All biological processes (ATP synthesis, muscle contraction, DNA replication) are governed by Gibbs free energy.

→A refrigerator doesn't create cold - it moves heat from inside to outside, in compliance with the second law.

→Maxwell's demon (1867) - a thought experiment suggesting entropy could be violated - was not resolved until 1961.

🔗 Nuclear Connection

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☢️ Nuclear Elements 🏥 Radiation & Health 🔋 Fuel Cycle