Question

A set of data was recorded for the reaction of decomposition of H2O2. The data is shown in table 3 Copy the data from table 3 in an Excel spreadsheet. Table 3 Time (min) [H2O2] 0 0.300 1 0.221 5 0.107 10 0.065 15 0.047 20 0.037 In Excel, add two columns to calculate the ln and inverse of the concentration. Make a prediction (guess) which order the reaction is with respect to H2O2. Plot the data and see if the plot obtained is linear, if it’s not change your prediction (guess again). For example, if you predict that the order of the reaction is zero, you will plot the data in the column [H2O2] vs time. If the plot you obtain is liner, you will have found out that the order of the reaction with respect to H2O2 is zero. If the plot is not linear, you will conclude that the order of the reaction with respect to H2O2 is NOT zero but you still will not know if it is first or second order. To find out, you will have to build another plot until you find a linear one.

When you finish, answer the questions below 1. Which plot is linear? 2. What is the order of the reaction with respect to H2O2? 3. What is the value of k? 4. Write the rate law for the reaction.

Answer 1

The decomposition of (hydrogen peroxide) is given as below.

Hence the rate law of the equation can be written in the form as

where

Now our target is to find whether (zeroth order, first order, second order ... and so on) while plotting the concentration versus time graph.

Given data table

Time (min)
0	0.300
1	0.221
5	0.107
10	0.065
15	0.047
20	0.037

Now inorder to check we plot different graph for different orders, which are explained below.

Prediction 1: To check if its Zero Order

IF our order of reation is 0 then our rate law can be rewritten as,

Hence

We integrate this expression

which gives us the final asnwer as

where

Hence if we plot a graph of v/s we get a straight line of slope and intersection at y axis at IF IT IS A ZEROTH ORDER REACTION.

Hence from the graph as it is NOT A STRAIGHT LINE it is NOT A ZEROTH ORDER reaction. i.e. .

Prediction 2: To check if its First Order

A student must note that we have to redo all the derivation with . For first order to check whether the graph is linear, we need to plot a different concentration function v/s time graph. Below is the derivation for the same.

IF our order of reation is 1 then our rate law can be rewritten as,

Re arranging the equation and taking integral we get

Solving this we get

Re writing the equation

Hence if we plot a graph of v/s we get a straight line of slope and intersection at y axis at IF IT IS A FIRST ORDER REACTION.

Hence from the graph as it is NOT A STRAIGHT LINE it is NOT A FIRST ORDER reaction. i.e.

Prediction 3: To check if its Second Order.

IF our order of reation is 1 then our rate law can be rewritten as,

Re arranging the equation and taking integral we get

Solving this we get

Hence if we plot a graph of v/s we get a straight line of slope and intersection at y axis at IF IT IS A SECOND ORDER REACTION.

Hence from the graph as it is A STRAIGHT LINE it is A SECOND ORDER reaction. i.e.

1) Hence the third plot is linear. That is when the decomposition is second order reaction the plot is a straight line.

2) The order of the reaction with respect to is a second order reaction.

3) As mentioned earlier the value of slope will be , which from the graph is 1.188. Hence the value of the rate constant, is given by

Hence value of

4) The rate law of the reaction can be written as

Unit of r --->