Jan_28_09 - Determine concentration at any time d[A]/dt =...

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Wednesday, Jan 28 Chemistry 108
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First order process n=1 dc/dt =Rate = -kc n = -kc If R = 2M/s for c = 1M And R = 4M/s for c = 2M 1 st order Ratio R 2 /R 1 = (c 2 /c 1 ) n 4/2 = (2/1) n n=1
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First order half lives 1M t 1/2 = 10min 2M t 1/2 = 10min • [t 1/2 (2)/t 1/2 (1)] = [C 1 /C 2 ] n-1 note inversion Think about rates and zero order reaction
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Summary of First order A → P (Product) R = Rate = d[A]/dt = -k[A] 1 Each molecule independent Not our normal view of time • k = 0.7/t 1/2 always same t 1/2 to halve concentration
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Sample Question A first order irreversible reaction has a concentration of [A o ] = 16mM at t=0. After 10s, [A(t)] = 4. A) Write the rate equation • B) Determine t 1/2 C) Determine k D) Determine the Rate of reaction at 10s.
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Unformatted text preview: Determine concentration at any time d[A]/dt = -k[A] [A] = [A o ]e-kt e = 2.78 e-1 = 1/2.78 = 0.37 Log (10) = 1 ln(e) = 1 Ln[A(t)] = ln{[A o ]e-kt } ln(xy) = ln(x) +ln(y) Ln[A(t)] = ln[A o ] +ln(e-kt ) = ln[A o ] kt y = b + mx straight line Y = ln[A(t)] b = [A o ] m = -k x = t Ratio method 1 st order Rates R 1 = - kc 1 R 2 = - kc 2 R 2 /R 1 = {c 2 /c 1 } 1 R 1 = 2M c 1 = 1M R 2 = 4M c 2 = 2M (4/2) = (2/1) 1 so 1 st order Half Lives First order c 1 = 2M t 1/2 = 5s C 2 = 4M t 1/2 = 5s {t 1/2 (1)/t 1/2 (2)} = (c 2 /c 1 ) n-1 n-1 = 0 for 1st...
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Jan_28_09 - Determine concentration at any time d[A]/dt =...

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