lec26 - Thermodynamics What we are studying System...

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1 Thermodynamics • Studies heat and work • Heat – How energy is transferred, temperature change • Work – moving an object against a force System Surroundings What we are studying Everything else First Law • Energy conservation – total energy is shared between heat and work, U = q + w • Found for P–V work that w = – P Δ V – when Δ V is + U is lower – when Δ V is – U is higher Δ U = q – P Δ V Enthalpy • Tough to measure Δ U, q is easier – calorimetry • New parameter – Δ H Δ H = Δ U + P Δ V = q • Heat released or absorbed at constant pressure Δ H°– standard enthalpy Δ H at 1 atm on a pure substance Uses of First Law and Enthalpy • Heat capacities – temperature changes within a given phase • Enthalpy of change – heat required for phase changes • Reaction enthalpy Δ H f = Σ nH° f (products) - Σ nH° f (reactants) Direction of Change • Why … – do reactions go to equilibrium? – does anything happen?
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lec26 - Thermodynamics What we are studying System...

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