Week 02 - Instructor - Gener a l Chemi str y I I G ener CH...

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General Chemistry I I CHEM 152 Week 2
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UA GenChem Week 2 Reading Assignment Chapter 13 – Sections 13.2 (rate), 13.3 (rate law), 13.4 (integrated rate law)
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UA GenChem A more refined description The average reaction rate gives us information about the speed of the reaction over a certain period of time. But what if we are interested in a more detailed description. How do we calculate the instantaneous reaction rate at any particular time? 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01 0 200 400 600 800 1000 1200 1400 1600 1800 2000 Time, min Concentration, mol/L
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UA GenChem START END Different Rates During a Reaction Overall average rate Initial Rate (slope of the line At a point)
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UA GenChem time . From your lab experience, how could we follow the course of this reaction? Measure rates? What’s changing? What could we measure? Measuring Rates Consider this reaction:
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UA GenChem time 393 nm light Detector [Br 2 ] Absorption 393 nm Br 2 ( aq )
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UA GenChem Average rate = - [Br 2 ] t = - [Br 2 ] final – [Br 2 ] initial t final - t initial slope of tangent tangent tangent Instantaneous rate = rate for specific tiny instance in time
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UA GenChem R A T E rate α [Br 2 ] rate = k [Br 2 ] + 0.0 k = rate [Br 2 ] = rate constant = 3.50 x 10 -3 s -1 Y=mX+b Constant = Slope = k How do the RATES Rate = k [Br 2 ] 1 this is called a 1 st order reaction Rate Law The rate law for a reaction tells us how rate varies with concentration of the reactants.
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UA GenChem SOLUTION: For each of the following reactions, determine the reaction order with respect to each reactant and the overall order from the given rate law. (a) 2NO(g) + O 2 (g) 2NO 2 (g); rate = k[NO] 2 [O 2 ] (a) CH 3 CHO(g) CH 4 (g) + CO(g); rate = k[CH 3 CHO] 3/ 2 (c) H 2 O 2 (aq) + 3I - (aq) + 2H + (aq) I 3 - (aq) + 2H 2 O(l); rate = k[H 2 O 2 ][I - ] (a) The reaction is 2nd order in NO, 1st order in O 2 , and 3rd order overall. Your Turn
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UA GenChem Consider the reaction: 2A + 2B + C 2D + E If the rate law for this reaction is Rate = k[A][B] 2 Your Turn What is the effect on the rate if the concentration of A is doubled? 1. No change 2. x2 3. x4 4. x8 5. x16
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UA GenChem What is the effect on the rate if the concentrations of A, B & C are all doubled? Rate = k[A][B] 2 1. No change 2. x2 3. x4 4. x8 5. x16
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UA GenChem The reaction: 2NO(g) + 2H 2 (g) N 2 (g) + 2H 2 O(g) Is found experimentally to be second order in NO(g) and first-order in H 2 (g). 1)Write the rate law given the above data. 2)If the concentration of NO is doubled, what will the effect be on the rate?
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Week 02 - Instructor - Gener a l Chemi str y I I G ener CH...

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