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10.01b - Internal Energy E = KE PE(sum over all particles...

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1 Internal Energy E = Σ KE + Σ PE (sum over all particles) When E in one system changes: Δ E > 0 Δ E < 0 (energy of syst (energy of syst goes up) goes down) E from surroundings E into surroundings How does E flow? As work ( w ) or heat ( q ) Δ E = q + w q > 0 endo thermic (heat in) q < 0 exo thermic (heat out) Defined from point of view of system! For example 2 H 2 (g) + O 2 (g) ---> 2 H 2 O (g) + heat, exo thermic 2H 2 + O 2 2 H 2 O Potential energy Δ PE Nuclei move (reaction coordinate) Atoms move “downhill” and energy is released (exothermic)
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2 Flow of Heat, II Melting ice – Endo thermic – Heat must go in. Where does it go? Energy of motion!! (also position changes a little) Work as Energy Flow Expansion of gas When a gas expands, it can do work on surroundings (car piston) It takes work to compress a gas. Work as Energy Flow Compression of gas (the Lyle demo) Gas “pushes” syringe up: P = F/A Work = force • distance Do work on gas --> energy goes in. But where?
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