Activation Energy Cannon_Thermochemistry Key 3: Activation Energy
Instructions:
Review and Complete “Thermochemistry” Synapse page
Complete one or more of the activation activities presented in the lesson
Key #3: Activation Energy
In chemistry and physics, activation energy is the energy which must be provided to a chemical or nuclear system with potential reactants to result in: a chemical reaction, nuclear reaction, or various other physical phenomena.
The activation energy (Ea) of a reaction is measured in joules (J), kilojoules per mole (kJ/mol) or kilocalories per mole (kcal/mol).
Activation energy can be thought of as the magnitude of the potential barrier (sometimes called the energy barrier) separating minima of the potential energy surface pertaining to the initial and final thermodynamic state. For a chemical reaction, or division[ to proceed at a reasonable rate, the temperature of the system should be high enough such that there exists an appreciable number of molecules with translational energy equal to or greater than the activation energy.
In simple language..
Activation energy is the minimum amount of energy required to start a reaction.
Consider a large boulder on a hill. Because the boulder is on the hill, it contains gravitational potential energy. However, the large mass and thus the inertia of the boulder is to stay put. Only by giving the boulder an injection of energy, a push over the edge, can the potential energy be released.
Once the boulder drops over the edge it will release its potential energy generating lots of heat in the form of destruction as it rolls into a valley of stability where it will stop.
The heat that is generated from the release of gravitational potential energy can be measured, and this is how activation energy connects with Enthalpy, and thermochemistry.
The Aluminum Activation Cannon
In our final example, and the activity which I hope most of you will attempt…SAFELY!!!…brings us back to matches.
Typically, the chemical potential energy in the phosphorus and chlorate is activated through the addition of energy provided by the friction of striking the match against the box. However, to gain insight into activation energy we can create an aluminum “barrel” into which we can place a match thereby preventing a lighter from igniting the match. We can then take the lighter and start to add heat to the aluminum barrel. Eventually this heat will transfer to the head of the match and provide enough energy to activate the match. At this point the gas pressure should build in the barrel and shoot the match into a carefully chosen direction containing no other flammable materials.
The activation energy of the match is provided by conduction rather than friction. This leads us to our next lesson on how heat energy travels…
Be safe when conducting experiments with matches. Ensure proper ventilation, and keep a some water near by to deal with any unintentional fires. Remember that Colorado is a giant tinderbox just waiting for a stray spark to activate the entire state into a fire.
Also, have fun and let me know if you actually get the match to shoot out of the barrel. We tried many time and its much more difficult than it might seem.
Good luck on your mission
Mr. Reynolds
Key Vocabulary
gravitational potential energy (GPE) - is the potential energy a physical object with mass has in relation to another massive object due to gravity. GPE of an object that depends on its mass and its distance from the center of mass of another object
Chemical potential energy - is the potential of a chemical substance to undergo a chemical reaction to transform into other substances. Examples include batteries, food, gasoline, and etc. Breaking or making of chemical bonds involves energy, which may be either absorbed or evolved from a chemical system.
Match - a match is a tool for starting a fire. Typically, matches are made of small wooden sticks One end is coated with a material that can be ignited by frictional heat generated by striking the match against a suitable surface. The coated end of a match, known as the match "head", consists of a bead of active ingredients and binder; often colored for easier inspection. There are two main types of matches: safety matches, which can be struck only against a specially prepared surface, and strike-anywhere matches, for which any suitably frictional surface can be used.