chapter_18_handouts

chapter_18_handouts - 4/1/2009 Entropy, Free Energy, and...

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4/1/2009 1 Entropy, Free Energy, and Equilibrium Chapter 18 Spontaneous Physical and Chemical Processes • A waterfall runs downhill • A lump of sugar dissolves in a cup of coffee • At 1 atm, water freezes below 0 0 C and ice melts above 0 0 C • Heat flows from a hotter object to a colder object • A gas expands in an evacuated bulb • Iron exposed to oxygen and water forms rust spontaneous nonspontaneous 18.2 spontaneous nonspontaneous 18.2 Does a decrease in enthalpy mean a reaction proceeds spontaneously? CH 4 ( g ) + 2O 2 ( g ) CO 2 ( g ) + 2H 2 O ( l ) Δ H 0 = -890.4 kJ Spontaneous reactions H + ( aq ) + OH - ( aq ) H 2 O ( l ) Δ H 0 = -56.2 kJ H 2 O ( s ) H 2 O ( l ) Δ H 0 = 6.01 kJ NH 4 NO 3 ( s ) NH 4 + ( aq ) + NO 3 - ( aq ) Δ H 0 = 25 kJ H 2 O 18.2
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4/1/2009 2 Entropy (S) is a measure of the randomness or disorder of a system. order S disorder S Δ S = S f - S i If the change from initial to final results in an increase in randomness S f > S i Δ S > 0 For any substance, the solid state is more ordered than the liquid state and the liquid state is more ordered than gas state S solid < S liquid << S gas H 2 O ( s ) H 2 O ( l ) Δ S > 0 18.3 W = 1 W = 4 W = number of microstates S = k ln W Δ S = S f - S i Entropy W = 6 Δ S = k ln W f W i W f > W i then Δ S > 0 W f < W i then Δ S < 0 18.3 Processes that lead to an increase in entropy ( Δ S > 0) 18.2 How does the entropy of a system change for each of the following processes? (a) Condensing water vapor Randomness decreases Entropy decreases ( Δ S < 0) (b) Forming sucrose crystals from a supersaturated solution Randomness decreases Entropy decreases Δ S <0
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This note was uploaded on 01/31/2010 for the course CHEMISTRY 51 taught by Professor Entus,r during the Fall '09 term at Mt. SAC.

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chapter_18_handouts - 4/1/2009 Entropy, Free Energy, and...

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