I need some help with these 2 questions. Thanks! 4.2 The rates of reaction of su
ID: 994954 • Letter: I
Question
I need some help with these 2 questions. Thanks!
4.2 The rates of reaction of substituted benzoyl chlorides with excess methanol at 0°C were measured. The pseudo-first-order rate constant for p-methylbenzoyl chloride is 0.0178 mol min and for p-nitrobenzoyl chloride is 0.413 mol/l min. Calculate the rate constant for m-bromobenzoyl chloride, assuming these two exam- ples give a good correlation [39. (Of course, in a proper study a larger set of examples would be used to obtain a correlation.) 6 The following reaction occurs in CCI at 25°C [43] CI CI I CI CH3 CHs CH3 CH3 Kinetic measurements were made following the concentration of ICi, using a large excess of C HICI. The data fit a linear plot as shown below. Write a rate expression for the reaction and calculate the rate constant. Run 1 0.0349 0.00441 Initial concentrations (M) Run 2 0.0174 C HICI, ICI 0.00160 800 748 625 476 227 200 400 600 800 1000 t(sec)Explanation / Answer
4.2 The -NO2 is electron wirdrawing group by resonance in nature and -CH3 group is electron withdrawing group by induction in nature. As we can see, the rate constant for p-NO2benzoyl chloride is much higher than p-Mebenzoyl chloride substrate. That means presence of electron withdrawing groups favors the rate constant of the given reaction. Now, -Br is an electron donating group by induction and exerts an electronegative pull for the shared pair of electron towards itself. Presence of it would lower the rate constant for the reaction. The inductive effect decreases with distance. So when the group is at ortho position, the effect is larger than when it is at the meta position of the substrate. The value for metabromobenzoyl chloride would fall between Me and NO2 substituent. Thus looking at the two values, we can predict the value of rate constant to be about 0.02.
4.6. The plot of 1/[ICl[ vs time is a straight line plot, this means that the reaction is second order with respect to [ICl] concentration.
The rate law for the reaction ths would be,
rate = k[ICl]^2
A second order reaction.
with,
k = rate constant = slope = (476 - 227)/1000 = 0.249 M-1.s-1