In this exercise we will calculate the concentrations of A and B as a function of time by numerical integration of the differential rate law using Euler's method given by
x2 = x1 + f(x1,t1)( t2-t1).. General directions for spreadsheet operations are given in the turtorial of Virtual Lab Simulator - Part 1. We will also construct a "slider bar" in the Integral method sheet that will allow us to vary the rate constant k and interactively see the changes on the concentration vs. time graphs. This is a useful tool to show students how changing a parameter affects the behavior of the system. It is also much easier to do than have students change numbers in cells to experiment with a model.

For the first order reaction
The differential rate law

Differential Method
1. Open a spreadsheet and enter the following into the designated cell:
A1 as "First Order Reaction A-> B Differential Method", A3 as "a=", B3 as "1000", A4 as "k=", B4 as "1", B6 as "dA= -kAdt", C6 as "A = a-dA", D6 as "B=a-A", A7 as "t", B7 as "dA", C7 as "A", D7 as "B", E7 as "lnA".


2. Let A8 to be 0, A9 to be 0.1, A10 to be 0.2 and so on. Fill cells A11 to A108 so that A108 will contain 10.0.
Let B8 to be 0, C8 to be 1000 and D8 to be 0. Let B9 to be =-$B$4*C8*(A9-A8), C9 to be =C8+B9, D9 to be =1000-C9 and E9 to be =LN(C8). Fill down B9, C9, D9 and E9 through B108, C108, D108 and E108.


3. Plot A and B against t. Plot ln A against t.

4. Building a Slider Bar
a. Choose View > Toolbars > Forms from the pull down menu. You should see the forms menu below:


b. Click the slider bar icon, then click on an empty space in the worksheet. You should see a very large slider bar appear. Adjust the size of the slider bar (narrower and longer) by
dragging on a highlighted corner. NOTE: If the slider is not selected, clicking on it will move the entire slider rather than selecting it. To select it, right click on it so that it appears as shown below.

c. Make sure the slider is selected, then double click the slider bar to bring up the Format Control window: Change the maximum value to 200 (See above). In the Cell link: window, type in C4 as shown. This will be the cell that our slider bar will control. Click OK to close the Format Control window.


d. In cell B4 (where the value for k is located), type ¡§=1/100*C4¡¨. What now happens is this: Our Slider bar will control cell C4 which drives cell B4 (the rate constant) to change values between 0 and 2 in increments of 0.01. Click and drag the slider and observe the changes in the spreadsheet values and graphs.

Click to see a video demo of how to build a Slider Bar. In order to play these videos, you should have flashplayer plugin installed. You can download the plugin from