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Chemical Reactions: Energy
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Reaction Rates, Catalysis, and Energy: Energy in making and breaking bonds.
Anytime a bond is formed, chemical energy in individual atoms is converted into heat energy. This is because the individual atoms are going from an unstable form (ie high energy) to a more stable form (ie low energy). Some of the excess energy heats the surroundings. The model below contains many separate atoms that will react by forming a bond. The amount of chemical energy converted into heat energy depends upon the strength of the bond formed.
To the right of the model is a temperature graph, and to the left is a controller that allows you to set the strength of the bond that will form between the A atoms. Experiment with the model to determine the relationship between bond strength and heat energy released. When you run the model observe what happens to the temperature. Then reset the model and try adjusting the bond strength before running the model again.
EXPERIMENTING WITH THE MODEL
1. Adjust the strength of the bond that will form. (Click on the link to learn how to adust this.)
2. Run the model.
3. Observe the behavior of the model and the temperature graph to the right of the model.
4. Reset the model, and repeat the above steps, but change the bond strength to some different value.
The model below will allow you to test your prediction about temperature and bond breaking. Run the model to test the hypothesis you stated in the previous question. This model will run in super-slow-motion mode, so you can focus on what happens to the temperature when the bond breaks.
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<font face="Verdana, Arial, Helvetica, sans-serif" size="4">A hot cup of
coffee or an ice cold glass of water left long enough on a counter top
will become "room temperature." Why don't our bodies become "room
temperature?" People maintain a body temperature of about 98.6°F. How do
we do this?<br><br>The secret is chemical reactions. During chemical
reactions heat can either be absorbed or released. We get the chemical
energy we need from the food we eat. It is the heat released from chemical
reactions in our bodies that keeps us at a constant 98.6°F.</font>
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<font size="4" face="Times,serif"><strong>What evidence did you see that chemical energy is converted into heat energy when bonds are formed during a chemical reaction?</strong></font>
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<font size="4" face="Times,serif"><strong>What is the relationship between the amount of chemical energy that can be released and the strength of the bond that will be formed? In other words, which substance has more chemical energy, one that can form strong bonds or one that can form weak bonds? Explain how you know.</strong></font>
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<font size="4" face="Times,serif"><strong>PREDICT: If chemical energy is converted into heat energy when bonds form, what do you think will happen to the temperature of a substance if bonds are breaking?</strong></font>
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<font size="4" face="Times,serif"><strong>Was your prediction about the temperature change during bond breaking correct? What did you observe that supported your prediction or did not support your prediction?</strong></font>
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<font size="4" face="Times,serif"><strong>When a bond forms, chemical energy is converted into heat energy causing the temperature to go up. What must happen to both the chemical and heat energy when a bond breaks?</strong></font>
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