Chemistry 30

Iowa State University, Tom Greenbowe

An assortment of online simulations and animations demonstrating aspects of chemical kinetics. Generally instructions are not provided.

Destruction of Ozone by CFCs

An excellent movie from Prentice Hall. General Chemistry: Principles and Modern Applications

Destruction of Ozone by NO

An excellent movie from Prentice Hall. General Chemistry: Principles and Modern Applications

Doing Chemistry Series

• Hot Penny Catalysis
• Catalyzed Burning of Sucrose

Iodine Clock Reaction

Iodine Clock Reaction Videos. Several Sources:

• Chemistry Comes Alive!
• University of Regensburg (P. Keusch)
• Microscale Iodine Clock Reaction (Doing Chemistry Series)

Doing Chemistry: Temperature and Reaction Rate

The effect of temperature on glosticks.

Comparing Reaction Rates - Lesson 1.1

Some quick demonstrations may be used to get students attention at the start of this unit. Questions to consider: What is meant by "rate of reaction"? How can you measure the rate of a reaction? Why are some reactions slow and others fast? Some suggestions for demonstrations:

1. Slow reaction - have an iron nail sitting on the desktop, slowly (imperceptibly) rusting.
   
   4 Fe_(s) + 3 O_{2 (g)} → 2 Fe₂O₃(s)
   
   
2. Relatively slow - the decomposition of hydrogen peroxide, H₂O₂. Pour some fresh hydrogen peroxide in a beaker and either place the beaker on an overhead or pass the beaker around the room for students to make observations - do they see any evidence of a reaction occurring? The odd bubble of oxygen gas may appear, but the reaction is generally too slow to observe.
   
   2 H₂O_{2 (aq)} → 2 H₂O_(l) + O_{2 (g)}
   
   
3. The hydrogen peroxide decomposition reaction may be sped up considerably by the addition of a catalyst.
   
   Possible catalysts to use: manganese dioxide, MnO₂ ; potassium iodide, KI; raw potato; blood; active yeast
   
4. A rapid reaction - reaction between zinc and hydrochloric acid
   
   Zn_(s) + HCl_(aq) → ZnCl₂ + H_{2 (g)}
   
   
   Materials:
   
   - balllon (an inexpensive type, with a thinner skin)
   - thread (to tie to the balloon once inflated with hydrogen gas)
   - large gas collecting bottle or other sturdy glass container - the balloon must fit over the bottle
   - zinc - pellets or mossy; not powdered
   - 6M HCl, 100 mL
   
   Procedure:
   
   Place 100 mL of 6M HCl in a large gas collecting bottle. Add the zinc and quickly cover the mouth of the bottle with the balloon. The balloon will rapidly inflate as hydrogen gas is generated during the exothermic reaction.
   
   While it is filling, ask students to think of ways to measure reaction rate for this particular reaction.
   
   After the reaction has slowed down and neared completion (15 - 20 min), carefully remove the balloon and tie it off, to be used for the next demonstration. Tie a thread to the balloon, which will float.
   
   Caution
   
   The reaction is quite exothermic; be sure that the foaming action of the reaction does not overflow the reaction vessel! The hydrogen balloon is very flammable!
   
5. A fast reaction - hydrogen gas explosion
   
   2 H_{2 (g)} + O_{2 (g)} → 2H₂O
   
   This demonstration also illustrates the concept of activation energy.
   
   Materials:
   
   - hydrogen-filled balloon from the previous demonstration
   - birthday candle taped to the end of a meter stick
   - matches to light the candle
   - safety equipment - goggles, fire extinguisher
   
   Tie the hydrogen balloon from the previous demonstration to a suitable object, so the balloon is suspended midway between a lab counter and the ceiling.
   
   Ensure safety precautions are followed - the use of eye goggles, make sure a fire extinguisher is readily available. This is a good time to review safety precautions with students.
   
   In a darkened room, light the candle and move it close to the balloon to ignite the hydrogen gas.
   
   

The Collision Theory - Lesson 2.1

Here are some ideas to get the students moving and involved in the concept of the Collision Theory. The first activity may be done best as a "thought" experiment.

• Have students clear a large space in the centre of the classroom of tables, chairs, and other obstacles. Blindfold the students (or have them close their eyes) and instruct them to walk slowly around the room. Collisions with other students indicate a chemical reaction will occur.

Extensions to this exercise:

• Sufficient energy required for a collision to be successful - Have students consider how collisions that occur when moving at an extremely slow pace will differ from those that occur at a more brisk walking pace. Note that a minimum amount of energy/speed is required for a collision to be successful.

• Orientation - Consider a reaction/collision to be successful only when one person steps on another's toes, or bumps shoulders.

• Effect of temperature - Increasing temperature increases the speed of the particles, as well as how much energy the reacting particles possess. How will running affect the number of successful collisions? Express this both in terms of more frequent collisions due to increased speed, but also more successful collisions due to the particles having more energy.

• Effect of increased concentration - How will increasing the number of students affect reaction rate (number of collisions)?

• Effect of a catalyst - another student, without a blindfold, may be used to help guide students towards the proper orientation for a successful collision.

The Paper Toss - An Introduction to Reaction Mechanisms

Have all students crumple a piece of paper into a ball.  Beginning with pairs of students, students should sit facing one another, close together. Instruct students to gently toss the paper balls towards each other, trying to get them to collide in the air. Out of ten tosses, how many successful collisions occur? Record the data for the entire class.

Next have the students form groups of three and repeat the ten tosses. For a collision to be successful, all three paper balls must collide simultaneously. Record the class data once again.

Finally, form larger groups and repeat. Students will quickly see that increasing the number of paper ball particles that must collide simultaneously quickly reduces the number of successful collisions that will occur.

Conclusion - Reactions in which more than two or three molecules must collide most likely occurs in more than one step.

Effect of a Catalyst on Reaction Rate - Lesson 4.4

Materials:

• hydrogen peroxide, H₂O₂
• Catalyst - options include manganese dioxide, MnO_2., liver, potato

Set Up:

I like to do this quick demonstration, along with other quick related demos, at the start of the unit to introduce several points:

• Reactions occur at different rates, and even spontaneous reactions can be very slow
• There are different ways to speed up chemical reactions - ask the students for ideas (stirring, heat, surface area, etc. are some ideas they may come up with)
• How can the rate of a reaction be measured? In this particular demonstration, a gas is evolved; measuring the volume of gas produced over time might be a useful measure of rate.

Procedure:

Pour a small amount of hydrogen peroxide in a beaker and pass around to the students (as safety, class size, etc. permits). Have students observe the reaction for signs of a reaction. This reaction is very slow, but a few bubbles indicating the production of a gas may be seen.

Ask the students to suggest ways in which reaction rates may be increased. This demonstration involves the use of a catalyst, MnO₂

Add a small quantity (less than 1 g) of MnO₂  to the hydrogen peroxide. Reaction rate is greatly increased and gas production is now clearly evident.

Safety:

Hydrogen peroxide is caustic to the skin and eyes. In case of contact, rinse well with water. Manganese dioxide is a strong oxidant. Avoid inhaling.

The reaction generates heat. Use only small amounts of manganese dioxide and use a heat-proof container.

Variations:

Alternatives to MnO₂ include potassium iodide (KI), raw liver, active dry yeast.

Effect of a Catalyst on Reaction Rate - Elephant's Toothpaste - Lesson 4.4 and Lesson 2.2

Another dramatic demonstration is the effect of a catalyst on the decomposition of hydrogen peroxide. This demonstration is commonly known as "The Elephant's Toothpaste."

Materials:

• hydrogen peroxide, H₂O₂, 50 mL
      (Typical drugstore H₂O₂ is only 3%; a higher concentration will produce a more dramatic effect - 30% works best)
• dish soap
• sodium iodide, NaI, 12 g

Set up:

This will get a bit messy as the reaction will overflow the container. Iodine will stain, so be sure to cover the demonstration area or carry this out in a sink.

Safety:

Hydrogen peroxide is caustic to the skin and eyes. In case of contact, rinse well with water.

The reaction generates heat. Use a heat-proof container.

Procedure:

Place about 50 mL of hydrogen peroxide into a container such as a large (500 mL) graduated cylinder or Erlenmeyer flask. Add a squirt or two of dish soap.

Quickly add the sodium iodide and stand back!

Explanation

The iodide ion, I^- catalyzes the decomposition of the hydrogen peroxide: H₂O_{2 (l)} → O₂(g) + H₂O_(l)

The reaction mechanism (lesson 2.2) for this reaction:

Step 1:   H₂O₂ + I^- → H₂O + IO ^-

Step 2:   H₂O₂ + IO^- → H₂O + O₂ + I^-

Effect of Surface Area on Reaction Rate - Lesson 4.1

Materials:

• flour
• large coffee can with lid
• candle
• 3 ft of tubing
• small plastic or metal can
• bunsen burner
• spatula or spoon

Set Up:

Make a hole on the side of the large can near the bottom. The hole should be just large enough to insert the tubing.

The small can will hold the flour and should be upright and in the middle of the large can.

The candle is also placed inside the large coffee can.

Procedure:

This demonstration may require some practice before you present it to your students.

Begin by showing that flour is not very flammable under normal conditions by trying to burn some flour on a spoon.

When finely dispersed the reaction goes much faster. Light the candle. Put the lid on the large can and blow long and hard into the tubing.

You should hear a "whump" as the lid will blows off the can and a brief flame appears.

Safety:

Wear safety glasses and have an extinguisher nearby. Be sure to practice the demonstration before showing to students.

Variations:

wood dust, lycopodium powder may be used instead of flour

View a demonstration:

• DoChem Experiments

Effect of Surface Area on Reaction Rate - Lesson 4.1

A very simple, quick demonstration of the effect of surface area on reaction rate. View this demonstration.

Materials:

• Ethyl alcohol
• Spray bottle (an old Windex bottle for example)
• beaker
• candle and matches

Procedure:

Demonstrate how ethyl alcohol burns by placing about 50 mL in a beaker and lighting it on fire. A nice blue flame will result. Careful - the beaker will get too hot to touch very quickly!

Next light the candle in its candle holder (such as a glass plate), keeping it far away from students. Squirt some alcohol from the spray bottle at the flame. A large fireball will appear, then quickly go out.

This is very effective in a darkened room.

Safety:

The beaker with the burning ethyl alcohol will get quite hot. Be sure to let it cool completely before moving.

Be sure to use the spray bottle far away from students and flammable objects.

Have a fire extinguisher nearby. Wear safety goggles.

Catalysts

The Prentice Hall site for General Chemistry: Principles and Modern Applications has a number of very good movies illustrating catalytic action.