energy changes in reactions
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Energy Changes in Reactions. Physical Science December 7, 2011 Ms Cilli Pages 206-209. Objectives. Describe the energy changes that take place during chemical reactions. Classify chemical reactions as exothermic or endothermic. - PowerPoint PPT PresentationTRANSCRIPT
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Energy Changes in Reactions
Physical ScienceDecember 7, 2011
Ms CilliPages 206-209
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Objectives• Describe the energy changes that take
place during chemical reactions. • Classify chemical reactions as
exothermic or endothermic. • Explain how energy is conserved during
chemical reactions.
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What type of reaction is this? C3H8 + 5O2 3CO2 + 4H2O
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What is chemical energy?
• Chemical Energy:
• Chemical reactions involve the ________ of bonds in the reactants and the ________ of bonds in the products.
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Energy in or out?
Breaking bonds Forming Bonds
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Bonds, Chemical Bonds
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Remember Phase Changes?!?!
Is heat lost or gained?
1. A plastic bottle of water is placed in a freezer. After several hours, the water has frozen solid.
2. A chef places a stick of solid butter in a saucepan, and heats the saucepan over low heat on a stove. After several minutes, the stick of butter has melted.
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Will you either come in or go out?
Exothermic:
Endothermic:
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Is heat lost or gained? Exothermic or Endothermic?
1. A plastic bottle of water is placed in a freezer. After several hours, the water has frozen solid.
2. A chef places a stick of solid butter in a saucepan, and heats the saucepan over low heat on a stove. After several minutes, the stick of butter has melted.
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Exothermic reaction
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Exothermic Reaction Example
Heat is on the _____ side
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Endothermic reaction
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Endothermic Reaction Example
Heat is on the _____ side
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All together now
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Tale of Two ReactionsIs it endothermic or exothermic?
(Look and ask yourself what side the heat is on)
C3H8 + 5O2 3CO2 + 4H2O + 2220kJ
2HgO + 181.7 kJ 2Hg + O2
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Closure…one step closer
Which one is not one of the 5 types of chemical reactions?
a. synthesis b. decompositionc. single-replacementd. double-replacemente. All of these are chemical reactions
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ASSIGNMENT:• Independent Practice:
– Read section 7.3– Work on the study guide
• Homework:– Complete the section 7.3 HW– Due Thursday, December 8 by 8PM