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Mr. Quinn & Ms. Tom
February 24, 2014
Aim: How do we determine where energy goes in a chemical reaction?
Do Now:
List one reaction that increases the surrounding temperature, and one reaction the
decreases the surrounding temperature.
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•
The Laws of Thermodynamics
1. Energy cannot be created or destroyed
2. The disorder of a system increases over time
Two Types of Reactions
Exothermic Reactions
Endothermic Reactions
• Temperature increases
• Temperature decreases
• Energy is released
• Energy is absorbed
• Heat is a product
• Heat is a reactant
Example 1
Example 1
• Did the temperature of the surroundings increase or decrease?
• INCREASE
• Is the reaction pictured exothermic or endothermic?
• EXOTHERMIC
• Provide one justification for your answer to the previous question.
• TEMPERATURE INCREASED AND THERE WAS A FIRE
• Where was the energy released to?
• THE AIR
• Would you predict that the products have a higher or lower energy than the
reactants?
Example 2
Example 2
• Did the temperature of the surroundings increase or decrease?
• DECREASE
• Is the reaction pictured exothermic or endothermic?
• ENDOTHERMIC
• Provide one justification for your answer to the previous question.
• TEMPERATURE DECREASCED
• Where was the energy absorbed from?
• THE WATER
• Would you predict that the products have a higher or lower energy than the
reactants?
Let’s Try It Out!
Melting ice causes the temperature of the air When water vapor forms snow (deposition),
to DECREASE. Is the process of melting
the temperature of the air INCREASES. Is
exothermic or endothermic? Why?
deposition exothermic or endothermic?
Why?
Let’s Try It Out!
Dissolving table salt in water is endothermic. Burning Mg creates a hot white flame. Is this
What do you expect to happen to the
process exothermic or endothermic? Explain.
temperature of the water?
Let’s Try It Out!
A process is exothermic. Is energy a product
or reactant?
A process leaves products with less energy
than the reactants. Is it exothermic or
endothermic?
Your Turn!