Question

For a reaction, graphing the natural log of concentration vs. time produces a linear graph with a slope of -15.3/sec. However, the graphs of concentration vs. time and 1/concentration vs. time are not linear. The reaction is _____ order. What is the rate constant, including units, for the reaction? Reaction Order = _________ k = ____________________

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

From all data

we can assume that

this is FIRST ORDER due to the constant graph

b)

the rate constant is always, for 1st order

slope = -k

k = -(-15.3) = 15.3

the units are clearly 1/time = 1/seconds