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notes from class January 30th

# notes from class January 30th - Summary to date The...

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Summary to date The stoichiometry of the balanced reaction determines the relative rates of disappearance of reactants and appearance of products. •a A + b B cC + dD The experimental rate law describes the dependence of the initial rate on the concentration of the reactants The experimental rate law gives us clues as to how the reaction proceeds. We can use it to test proposed reaction mechanisms. The experimental rate law rate=k[A] n [B] m tells us how the rate of the reaction depends on the concentrations of the reactants and sometimes products of a reaction. n is the reaction order for A m is the reaction order for B and n + m is the overall reaction order.        11 1 1 dA dB dC dD ad t bd t cd t d d t 

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What is k? It is the rate constant for the reaction. It is independent of reactant concentration but does depend on temperature. All the experiments must be done under identical conditions. It tells us something about the energy required for the reaction to go, the activation energy. It also includes an “orientation factor”. More later Now determine the value and units of k. 8.0 x 10 -4 molL -1 /s = k(.1 molL -1 )(.1 molL -1 )((.1 molL -1 ) 2 ) -4 -1 -1 -3 -1 -4 -1 4 8x10 molL s k= =8 mo lL s 1x10 (molL )
The order of a reactant might not always be a whole number. Example: A + B C Experiment [A], mol/L [B], mol/L Rate, mol/Ls 1 .010 .010 2.4 x10 -2 2 .020 .010 4.8 x 10 -2 3 .020 .020 .136 rate = k[A] m [B] n Looking at experiments 1 and 2, Doubling the [A] doubles the rate. Therefore, Rate = k[A] 1 [B] n What is n? mn -2 -1 -1 -1 -1 m n n k(.2) (.1) 4.8x10 molL s = .136 molL s k(.2) (.2) 1 .352941176 = 2 ln(.352941176) = nln.5 n=1.5    It doesn’t matter which logarithm you use.

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For the reaction 2 NO( g ) + 2 H 2 ( g )
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notes from class January 30th - Summary to date The...

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