Question

6) The following gas-phase reaction was studied at 290°C by observing the change in pressure as a function of time in a constant-volume vessel: Determine the order of the reaction and the rate constant based on the following data: Time (s) Partial Pressure of CICO CCls (mmHg) 181 513 1164 15.76 12.64 8.73 4.44

Answer 1

For the reaction: (e)coq,(e) Strategy to solve the problem: P (Given) is the total pressure. In order to find out the rate constant we need to know Pcico2cci3. Once it is known to us we will plot a graph by taking pressure verses time. As a trial and error basis we will check out one by one. If a straight line is obtained then the corresponding order is known to us Parameters Nature of graph Order of the reaction InP Vs time Straight line First order Vs time Straight line Second order Pressure Vs time Straight line Zero order The slope of the line will be equal to rate constant.

Following are the steps to find out the Pcico2ccl3 CICO,CCI, () 2CoCI, (8) Initial (t 0) P o 0 Change (t = t)-x +2x Total pressure Po -X +2x Thus change in pressure is Ap-R-P)=x AP PcICO2CCI3 (P-Po) | (15.76.-AP) P (Total) Inp 15.760 15.76 2.7574750 18.883.12 12.64 2.536866 181 22.797.03 8.73 2.166765 513 27.0811.32 4.44 1.490654 1164

Let us plot the graph between InP Vs time first. nP Vs time y--0.0011x+2.7404 2.5 2 1.5 0.5 200 400 600 800 1000 1200 1400 time (s) So we obtained a straight line on plotting time Vs InP. Thus the given data corresponding to the first order reaction. Slope of the line is 0.0011 s1 Slope -k 1.10x103s-1