1aa3-2012-tut4-a

1aa3-2012-tut4-a - CHEMISTRY 1AA3 Week of JANUARY 30, 2012...

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CHEMISTRY 1AA3 Week of JANUARY 30, 2012 TUTORIAL PROBLEM SET 4 – QUESTIONS ______________________________________________________________________________ Page 1 of 5 1. The rate law for the reaction: F 2 (g) + 2 ClO 2 (g) 2 FClO 2 (g) is rate = k [F 2 ][ClO 2 ]. At 25 C, the rate constant for the reaction is 1.2 M 1 s 1 . Calculate the rate of the reaction at 25 C if [F 2 ] = 0.010 M and [ClO 2 ] = 0.020 M. SOLUTION: rate = k [F 2 ][ClO 2 ] and k = 1.2 M 1 s 1 rate = (1.2 M 1 s 1 )(0.010 M)(0.020 M) rate = 2.4 10 4 M/s 2. Can you convert a second order reaction into a pseudo-first order reaction? a. Give an example: SOLUTION: Ester hydrolysis is the example used in class. It involves the stchiometric reaction between an ester molecule and a water molecule. Additional examples are hydrolysis of analogous hydrolysable functional groups such as amides, anhydrides, …, as well as all reactions between nucleophiles (water, hydroxide, amines, thiols…) and electrophiles (esters, anhydrides, primary (unhindered alkylhalides that undergo SN2 reactions). b. Explain the difference between a true 1st order, and a pseudo-1st-order, reaction. SOLUTION: A true first order reaction would be the substitution of a sterically hindered, tertiary alkyl chloride such as the t BuCl discussed in class, with nucleophiles. Here, the kinetics (rate of reaction) is determined by the initial slow step of alkylhalide decomposition into the intermediate cation and the chloride anion. A pseudo-first order reaction is one that is inherently second order, such as hydrolysis of an
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1aa3-2012-tut4-a - CHEMISTRY 1AA3 Week of JANUARY 30, 2012...

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