Captivating Activation
Source file content last modified: 4/17/15 12:46:58 PM
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Description

A potential energy barrier similar to an activation energy is modeled by a rubber device cut from half of a racquet ball. When the rubber device is turned inside out and dropped from a small distance onto a hard surface, the device snaps into its preferred shape and pops considerably higher than the point from where it was dropped. A Ping-Pong ball can be "launched" from the device with considerable velocity. This suggests an exergonic reaction in which some activation energy must be added before reaction can proceed.

Introduction

Very often, a flame or spark of energy is needed to initiate a reaction. This spark is known as the "activation energy," and it helps give the reactant particles the extra energy they need to collide effectively and initiate the reaction. The pilot light in a furnace or stove, the spark plug in a car's engine, and the flint and steel striker on a cigarette lighter all serve as reaction activators. The balls in this demonstration illustrate a physical potential energy barrier similar to the molecular energy barrier called the activation energy.

Chemical Concepts

Safety

Wear goggles. The flying rubber device and Ping-Pong balls can cause eye injury.

Procedure

  1. Invert a suitable piece of rubber device trimmed from half of a racquet ball. (See Lab Hints.) Hold it 3-5 cm from the surface of a table. Release. Note what happens. Repeat the drop from progressively higher and higher starting points. Note what happens.

  2. Repeat dropping the device with the concave side down (flat rim down). Note what happens.

Variation:

Questions

  1. Summarize your observations of the rubber device when inverted and dropped from 30 cm. Explain the energy changes at each step.
  2. Summarize your observations of the Ping-Pong ball when placed in the inverted rubber device and dropped from 30 cm. Explain any energy changes not discussed in answer 1.
  3. Chemists call the energy that is required to start a reaction, the activation energy. In this model, how is the activation energy added to the model.
  4. Can you name three ways to add the activation energy to a chemical reaction?

Handout Makeup

Name ___________________________ Class _______

Teacher __________________________

BeckerDemos 054: Captivating Activation

Watch the movies and answer the questions.

Curriculum-

Use this activity to demonstrate a model for the concept of activation energy.

Activity-

Demonstration - Student or Teacher

Safety-

Time-

Teacher Preparation: 10 minutes (each) to prepare the rubber device(s)

Class Time: 5 minutes

Materials-

Disposal-

Save the device for reuse.

Lab Hints-

  1. Construction of the the device, while simple, is nevertheless tricky. Obtain a new racquet ball. Squeeze the ball, and rotate it to locate the very thin equatorial seam. Mark it with a pen.

  2. Insert the point of a scissors (or a utility knife -- either way use EXTREME care) into the seam, and cut the ball into two halves along the seam.

  3. Use a scissors to trim along the edge of one of the halves. Trim it down a little bit at a time, and after each trimming, try inverting and dropping the piece from 30-40 cm onto a hard flat surface.* Continue trimming and testing until the device pops from the inverted (flexed) configuration to the normal (relaxed) configuration upon landing. If too much of the edge is trimmed away, the inverted configuration cannot be maintained, and often the difference between a device that works and one that does not is only a very thin sliver of device. There is no simple rule as to how much material to trim away; an empirical approach is required!

    * To invert the device, push on the outer surface until it snaps into an inside-out configuration. When drop testing it hold the inverted device horizontally, and drop it straight down with its concave (inside) surface facing downward. If it rotates while falling and hits on an edge, test it again; it may be ready, but just did not land correctly.

Observations-

Answers-

Q1. Summarize your observations of the rubber device when inverted and dropped from 30 cm. Explain the energy changes at each step.
A1. a. The rubber device drops to the table. The potential changes to kinetic energy.
b. On collision with the table the device inverts. The kinetic energy transferred to the device causes it to move over the potential energy barrier and invert itself.
c. After inversion the device bounces much higher than the dropping point. Once over the potential energy barrier, the extra potential energy, that was stored in the rubber device, is released. This energy is transferred to kinetic energy.
Q2. Summarize your observations of the Ping-Pong ball when placed in the inverted rubber device and dropped from 30 cm. Explain any energy changes not discussed in answer 1.
A2. Step a to c all take place in the second experiment also.
In addition, part of the energy from the inversion is transferred to the kinetic energy of the Ping-Pong ball. The ball bounces wildly as the energy is dissipated.
Q3. Chemists call the energy that is required to start a reaction, the activation energy. In this model, how is the activation energy added to the model.
A3. Dropping the device adds the energy required to invert it. This step corresponds to the activation energy. The rubber device does not invert without added energy.
Q4. Can you name three ways to add the activation energy to a chemical reaction?
A4. Heat, electric spark, light, and mechanical energy (pressure or grinding) are 4 possible methods.

Key Words 1-

model, model building, activated complex, exergonic, activation energy


This static was created at 12:46:58 PM on Friday, April 17, 2015