The learning objective of this educational module is to provide students with a pathway to understanding of the collision model in kinetics through an interactive demonstration on communication. This social and interpersonal experience will allow students to digest, anaylze, and effectively apply the collision model in their lives through unique activities and discussions.
After the module students will be able to:
-realize how the collision model is relevant to their lives
-coherently explain the collision model to themselves and others
-recognize the factors of a collision model
-realize the necessary collisions for a reaction to occur.
Background Summary:
A simple model that explains a reaction rate well for many reactions is the collision model. If we consider a simple reaction such as
A(g) + B(g) -> products
reactions occur when A and B molecules collide.
Any study of reaction rates and the rate at which molecules collide quickly shows that not every collision between molecules creates products; in fact, the vast majority do not. There are two basic reasons why not every collision is effective.
First, the molecules have to be oriented in the correct way. A very simple gas phase reaction such as Br(g) + HI(g) -> HBr(g) + I(g) won't occur unless the molecules are oriented such that the hydrogen is easily accessible by the bromine. This is known as the steric factor.
The second factor is due to the activation energy. Molecules are held together with strong chemical bonds. (The bonds need to be broken in order for new ones to form with different arrangements of atoms). In order to break these bonds, the colliding molecules have to have a large amount of kinetic energy from the collision. If they do not have enough energy, the reaction will not occur.
The collision model is important because collision models are relateable to other kinetic subjects such as Le Chatelier's Principle, Equilibrium, and Catalysts.
The collision model helps you understand reactions at a molecular level. When you understand how something works, you can improve, change, and fix it. This is a core principle that relates to environmental issues, a variety of reactions, and technology.
In an empty classroom blindfold a group of 10 or so students and walk slowly around the room. Occasionally, a pair of students will bump into one another. If they are moving slowly enough, nothing much will happen (that is, no pain upon contact). But if these blindfolded students begin running around the room (more speed = more energy), then a collision is likely to be successful (painfully so). If some students move about fast, while others stroll about at a more leisurely pace, successful reactions will still occur, but not as often as if all students are running.
Why are reactions not being formed when you bump into each other at a slow rate?
A) The molecules are not moving fast enough.
Wrong: Even if the molecules were moving fast, they would still not react if there wasn't enough contact.
B) The molecules are not colliding hard/strong enough.
Wrong: Even if the molecules collisions were strong, there would be very few if the molecules were not moving at a fast enough rate.
C) All of the above.
Next, have the students move at a brisk pace, but without running. This time, however, consider that collisions that occur shoulder-to-shoulder are not successful - your shoulders act as sufficient bumpers and collisions are not painful. But if one student steps on another's toes, then we have a successful collision! Let the movement begin.
What can we infer about collisions based on the fact that only toe-to-toe collisions count?
A) They must touch and overlap exactly, not just bump shoulders.
Wrong: Molecules do not have to overlap. As long as there is enough speed and force, they will react.
B) Molecules must have the right orientation for reactions to occur.
C) Collisions only occur when molecules move at the fastest pace possible.
Wrong: Molecules do not need exceptional speed. They can be moving at any sufficient pace if they also have the right orientation and force.
We find that of the frequent collisions that result, only a few will involve stepping on another's toes. This experiment helps us realized that collisions must occur with the proper orientation. Again, collisions between students will occur, but only some will be successful.
When we examine factors that increase the rate of a reaction, we will therefore look at factors that can influence at least one of the following of how often collisions occur:
more effective collisions in terms of collisions occurring with sufficient energy
more effective collisions in terms of collisions occurring with the proper orientation.
What can you do to increase the rates of a reaction? Pick the best answer.
A) Add more molecules and energy.
Wrong: Molecules need the right orientation to collide.
B) Add heat and catalysts.
Wrong: Only adding heat will not increase the rate of the collisions, as it does not add enough energy.
C) Add more molecules, energy, and orientation.
Following the activity, we will then debrief as a class through a discussion. This closure will lead students through an effective process of digesting and then applying the lessons from the structured activity to the life they see around them. They will also have a chance to thoroughly formalize their ideas and perceive the perspectives of their classmates through this closure.
Guiding Questions for Partner/Group Discussions:
1. What factors affect the rate of reactions?
2. Besides collisions, what two other factors must be considered for rates of reaction?
3. Define activation energy and activated complex.
4. Why does increasing the temperature increase the rate of reaction?
What is the main idea of collision theory? Pick the best answer.
A) The molecules collide with the right orientation, speed, and energy to produce more molecules.
B) The molecules collide with the right orientation, speed, and energy.
Wrong: When molecules collide, they make more molecules because throughout the process they bond with other molecules.
C) The molecules collide with the right orientation, speed, and energy to lessen the amount of molecules.
Wrong: When molecules collide, they do not form as one. Rather, they form new bonds and break off into different molecules.
Homework (if any):
*This can be done instead of the class discussion or vice versa.
To asses the students knowledge after the simulation, they will be teamed up with a partner to collaborate and further understand the topic. They will then give a presentation to the group on the background of the collision model, how/why it occurs, the key factors and points of the model, and how it is applicable to other subjects or everyday life.
They may use visual aids as they see fit to supplement their presentation. This assesment will allow others to percieve their peer's ideas and for all students to discuss ideas between themselves through collaboration.
Dealing with others, most interpersonal students will view this activity as a welcome challenge and visual learners will also benefit from a variety of unique presentations.
Hints:
First check your partners level of understanding. Then make sure you are both on the same page. If you need help explaining to them information they may have missed, contact a peer or teacher to assist you.
Draft your presentation. Try writing out an agenda to thoroughly outline your assesment and make sure each topic is covered and nothing is forgotten during the presentation. This will also help you recognize which visuals will be necessary.
Refer to the activities, discussion, or other key phrases mentioned the module provided you with. If you would prefer to come up with your own examples, that is also encouraged.
For the application portion of the presentation, team research may be required. Remember, what makes your presentation unique is the specific everyday life connection you make that is based off of the content learned from the collision model.
WARNING: ANSWERS BELOW
1. About the Collision Model
*See description in Background Section.
2. How/Why it Occurs
Collisions occur when molecules in the right orientation with the right speed hit eachother and combine. This results in the creation of two seperate molecules. This is because like molecules have the tendency to bond and when given the opportunity form their own molecules.
3. Key Factors of the Model
-Molecule Orientation
-Speed/Velocity
-Temperature
-Concentration
4. Real-World Applications
This section should be put together based on individual research or creativity. Though each of these should be unique, some examples include:
