CHM135H1 Lecture Notes - Ammonia, Activation Energy, Methanol

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31 Dec 2010
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LECTURE
13
Slide No. Notes
14 -nothing to do with rate
-spontaneous reaction can be slow or fast
-for instance, diamond to graphite is a very slow yet spontaneous
reaction
-if the forward reaction is spontaneous, the reverse is non-
spontaneous
15 - delta H is not enough to determine spontaneity
16 -S is a measure of disorder
-Entropy goes from localized to dispersion for spontaneous reactions
17 -gas particles are very spread out
-whereas solid particles are in ordered structures
18 -Ans1: B
-Ans2: A
-Ans3: B
-Ans4: A
-Second question:
-A) A2 (gas) + 2B (gas) -> 2AB (gas)
-B) negative S
19 -imagine two coins
-combinations of results are only HH; HT; TH; TT
-therefore 2 to the power of 2 is four
-imagine three coins
-combinations of results can be HHH; TTT; HHT; HTH; THT; TTH;
THH; HTT
-therefore 2 to the power of 3, which is 8
20 -solids vibrate faster, therefore higher entropy
-at BP, big jump in entropy because gas formed, particles very
spread out
-recall that at phase changes, the temperature does NOT change
21 -more entropy in drop of water than a bucket because entropy is an
extensive property
-Delta S = S of CaO plus S of CO2 subtract S of CaCO3 =
1mol(39.7J/Kmol) + 1mol times 213.6J/Kmol – 1 mol times
92.9J/molK = 160J/K
-This answer was expected to be positive so check!
22 -spontaneous – exogonic
-non-spontaneous – endogonic
-in Gibbs, surr incorporated by delta H of system
23 -note that the second sign is for delta S only, not the whole second
term including T
-negative H, positive S – negative G therefore reaction spontaneous
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Document Summary

Notes nothing to do with rate spontaneous reaction can be slow or fast for instance, diamond to graphite is a very slow yet spontaneous reaction if the forward reaction is spontaneous, the reverse is non- spontaneous. Delta h is not enough to determine spontaneity. S is a measure of disorder gas particles are very spread out. Entropy goes from localized to dispersion for spontaneous reactions. Whereas solid particles are in ordered structures. A) a2 (gas) + 2b (gas) -> 2ab (gas) B) negative s imagine two coins combinations of results are only hh; ht; th; tt therefore 2 to the power of 2 is four imagine three coins combinations of results can be hhh; ttt; hht; hth; tht; tth; More entropy in drop of water than a bucket because entropy is an extensive property. Delta s = s of cao plus s of co2 subtract s of caco3 = 1mol(39. 7j/kmol) + 1mol times 213. 6j/kmol 1 mol times.

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