Question

A flask is charged with 0.124 mol of A and allowed to react to form B according to the reaction

2 A(g) → B(g)

The following data are obtained for [A] as the reaction proceeds:

Time (s)	(ao – x) , M
0.00	0.150
10.0	0.111
20.0	0.0821
30.0	0.0608
40.0	0.0450

The order of the reaction is

first order

second order

third order

The numerical value (omitting the units) for the rate constant (to two significant figures and) for the reaction is

0.15

0.61

0.045

0.030

Answer 1

The best way to identify fast and easy the rate of reaction AND the rate constant is via Graphical Method.

First, as the name implies, we need to graph all types of order (most common)

Zero = C vs t;

For zero order, there is no dependency of concentrations:

dC/dt = k*C^0

dC/dt = k

When developed:

C = C0 - kt

if x axis is "time" then the slope is "k", and y-intercept is initial concentration C0. y-axis if C (concentration)

First = ln(C) vs. t

For first order

dC/dt = k*C^1

dC/dt = k*C

When developed:

dC/C = k*dt

ln(C) = ln(C0) - kt

if x axis is "time" then the slope is "-k", and y-intercept is initial concentration C0. y-axis if ln(C) (natural logarithm of concentration)

Second = 1/C vs. t

For Second order

dC/dt = k*C^2

When developed:

dC/C^2 = k*dt

1/C= 1/C0 + kt

if x axis is "time" then the slope is "k", and y-intercept is initial concentration C0. y-axis if 1/(C (inverse of concentration)

Know, graph all data in the 3 graphical methods

Best fit is 1st order (FIRST ORDER)

so

k = -slope = 0.0301

choose 0.03