Module 8: Unit 2. Factors Affecting Rate

Factors Affecting the Rate of Reaction

The Solution Chapter did discuss the factors affecting the rate of solubility. Similar factors are affecting the rate of reaction which will be adopted here as well.

1. Temperature:
The higher the temperature the higher the rate of the dissolution of the solute in the solvent
2. Surface area:
The higher the surface area of the solute, the higher the rate of the dissolution of the solute in the solvent. An example of this can be seen in the solubility of fine powder sodium chloride in water compared with the solubility of the coarse sodium chloride (rocky sodium chloride) in water. The fine powder sodium chloride has larger surface area and hence higher rate of dissolution in water.
3. Solute concentration:
The higher the concentration of the solute the higher the rate of dissolution in the solvent.
4. Catalyst: The use of catalyst increases the rate of reaction by decreasing the activation energy of the reaction. This is happening by re-routing the reactants through a rout with lower activation energy. The catalyst will be recovered, recycled and reused and it is not part of the products themselves.

The video below illustrates the factors that affect the rate of reaction:

Another video illustrates the effect of these factors which are affecting the rate of the reaction:

The Molecular Workbench simulation illustrates the effect of the concentration and the temperature on the rate of reaction.

One can access the simulation in multiple steps:

First one has to access the Molecular Workbench general website:

http://mw.concord.org/modeler/index.html

Second one has to look at the Selected Curriculum Modules and at the bottom of the section, one has to access more modules by accessing the link: More Modules

As soon as More Modules is selected a new Window with a dialog will appear:

Then select the option: Open with JAVA Web Launcher and then click OK.

As soon as OK is selected the Activity Center – Molecular Workbench Version 3.0 will open up and several simulations will be available. Select Rate of Reaction Simulation.

The simulation has many topics. The effect of Concentration on the Rate of Reaction is selected:

Click on the first step of the simulation:

Make notes of the reaction of oxygen atoms to produce the oxygen molecules in the larger container and then click the Back Arrow and follow the same reaction in the smaller container. Make your notes as well.

Now you are ready to answer the question:

Did it take a longer or shorter time for the oxygen atoms to react when they were more concentrated or when they were more spread out? Why?

Now click on the last step of the simulation: Increasing concentration by having more reactants:

Now you are ready to answer the question of the third step of the simulation:

Explain why oxygen atoms react more quickly in this large container than the first large container that had fewer atoms. Be sure to talk about the rate of collisions.

A Phet simulation illustrates the Reverse Reactions and the factors affecting them:

https://phet.colorado.edu/en/simulation/legacy/reversible-reactions

Reversible Reactions Simulation
Learning Goals:

1) Visualize a system at dynamic equilibrium state (DES)
2) Characterize the DES by finding the red : green ball ratio, Krg.
3) Design an investigation to test the effect of changing temperature, number of balls and activation energy barrier has on the

Part 1: Play

Instructions:
1) Open the PhET “Reversible Reactions” simulation.
2) Play with the simulation. Click on EVERYTHING!
3) Answer the following questions:

1) Put some number of balls (>50) in one of the wells. In a table, record the number of green and red balls in each well as a function of time. (Suggested time length: 5 minutes, suggested intervals: 15-20 seconds) Paste the table into this document. (Google spreadsheet will work well for this.)

2) Paste in a graph of your data. Describe the shape of the graph and what it means in terms of the red and green balls. Consider the ratio of red balls to green balls. How does that change over time?

3) After some amount of time, this simulation reaches a dynamic equilibrium state (DES). That is, a situation in which components of a system are moving but no net change is observed. Describe how this simulation fits this model in terms of the amount of red and green balls.

Part 2: Investigate
Instructions: Investigate, using available tools in the simulation, the effect of a change in temperature, # of balls or activation energy on the Krg. Your investigation must include the following factors (and fit onto the rest of this page):

● Experimental question (ie How does X affect Y?): (Check your question with Dr. White before beginning)
● Independent variable:
● Dependent Variable: The ratio of red : green balls. Let´s call it “Krg”. 
● Controlled Variables:
● Table
● Graph
● Conclusions (1 paragraph referring back to data)

Reversible Reactions Activity

1. Setup – Search “PhET Reversible Reactions” simulation. Open and run the simulation.

2. Explore! Click on everything to find the variables and observe how they affect the reaction. (Don’t just try to max out the computer’s memory chip.)

3. Reaction Conditions: Move the position of the reactants, transition state, and products wherever you wish and choose a temperature. Be reasonable!!

Reactants _______________ Transition state _____________

Products _____________ Temp ______________

4. Design! You will run three trials. Each one should have 100 total molecules. Start with different amounts of A and B for each trial. Place the starting amounts in the table at time 0. Record the amount of A and B in the chamber every 20 seconds for 5 minutes.

5. Which side of the reaction is favored (are there more reactants or products) for the experiment you set up? Why is that so?

6. Graph the concentration (number of molecules) of both molecules A and B vs time. You should have two separate curves (A and B).

7. What is happening to the concentrations at the beginning of the experiment? How does that differ from what is happening at the end of the experiment? Mark a vertical line on the graph at the point where equilibrium is established.

8. All three trials started at different amounts. How did the final ratios of A to B compare?

9. Did the reaction ever stop?

You Tube Video shows the effect of the Temperature on the Rate of reaction:

Also You Tube Video shows the effect of the Concentration on the Rate of reaction:

The Effect of the Surface Area of the Reactants on the Rate of Reaction is illustrated in the
You Tube video below:

The Effect of the Catalyst on the Rate of Reaction is illustrated in the
You Tube video below: