Reaction Rates |
Collision Model |
Catalysts |
Activation Energy |
Equilibrium |
LeChatelier’s Principle |
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Activation Energy
To identify activation energy on a graph
Chemical kinetics is the study and monitoring of chemical reactions. In a chemical reaction, two or more molecules mend together to create product. Out of all the possible reactions, they all react at different paces. Some stay unreactive for years. Others spotaneously react. The rate of the reaction differs through different points in the reaction. However, the rate of the reaction is not just measured by time. We also must consider concentration. Reaction rates are found by:
Reactions rates are affected by activation energy, our main concept below.
SKIING?
This figure compares activation energy, our concept, to a ski chairlift. Each of the skiers is a different reactant. The skiers come together at the top to go down. The top of the chairlift would be known as the activated complex. Going down the run would be similar to the product of a reaction. The flash animation looks similar to a graph we would use for a reaction.
COMPARING IT TO A GRAPH
The height from the bottom of the lift to the top would be the amount of activation energy. We use the variable Ea for activation energy. But, what is activation energy really? What does it mean? Activation energy is the energy that is need to make a reaction happen. In chemical reactions, activation energy is created by raising temperature. Raising temperature raises energy regardless of the topic. This speeds up a reaction. This is why some reactions can happen spontaneously. With less activation energy, reactions can stay inactive for a long time. Concentration also affects the reaction. Imagine replacing a chairlift. You would switch an old double chair to a new express six pack.
1. How is activation energy created?
A. Raising temperature
B. Add a catalyst
C. It's one of chemistry's few mysteries
2a. On this graph, which letter represents the activation energy?
2b. What variable do we really use?
A. E
B. A
C. G
D. Ea
CONCENTRATION/ENDO-EXO
- http://outdoors.mainetoday.com/downhill skiing/skibum/Riding%20chairlift%20I%20278.jpg
- http://library.mines.edu/ropeway/images/detachable_chairlift.jpg
You change the amount of people each chair could carry without changing the height and length of the chair. Concentration refers to a higher or lower number of molecules in a reactant. Therefore, you have more molecules in the product. Similarly, if you upgrade the chairlift, you can get more people on the mountain. The animation and the corresponding graph show an exothermic reaction. Exothermic means heat is leaving the system, or the reaction. When the skiers get to the bottom of the slope, they are lower than the bottom of the chairlift. When product is below the reactant, the reaction is exothermic. In an endothermic reaction (shown below), the product would have more energy or heat than the reactants. To remember endo and exo, think endo is into, exo is exit. Also, compare the endo and exo graphs. Notice anything similar? Well, they both have similar shape, but are flipped. This is even another way that shows that endo brings energy into, and exo lets it exit.
FINAL ASSESSMENT:
3. The animation at the top of the activity represents an endothermic reaction.
T. True
F. False
Answers Below:
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1. Correct answer: A. Raising temperature. Read the second part of the activity again.
2a. Correct Answer: D. Activation energy is the height from the reactants to the activated complex (highest amount of energy)
2b. Correct Answer: Ea. E stands for Energy. a stands for activation.
3. Correct answer: False, it represents an exothermic reaction. For it to be endothermic, energy must be absorbed, ending with a high energy product. If you imagine the animation as a graph, the energy of the product is low. This is because it lets energy out.
