Endothermic and Exothermic reactions

Today's Chemistry Cat!

Review

• all chemical reactions involve a change in energy 
• some absorb: indothermic endothermic
• some release: exitthermic  exothermic
• molecules are held together by chemical bonds
• add energy to break bonds
• give off energy to make bonds

reaction takes more energy to break then to make (bonds)= exothermic

reactions takes less to break then make (bonds) = 

endothermic

Endothermic and Exothermic Reactions

Entropy: heat contained in a system 

Energy Diagrams

• we can graph potential energy of chemicals as they under go a reaction
• relative amounts of energy determine if a reaction is endothermic or exothermic

Activated Complex: potential energy of the transition state between reactants and products

Activation Energy: energy that must be added to make the reaction to occur

DeltaH (change in entropy): change in potential energy during reaction (products - reactants)

Endothermic Energy Diagrams

• products will have more energy then the reactants (deltaH will be positive)

Exothermic Energy Diagrams

• products will have less energy then the reactants (deltaH will be negative

Try these!

exothermic vs endothermic quiz

this has the same ideas as above  

The first 6 questions are just looking at the graph and saying the answer. 

The last 6 questions are as if the graph is flipped...the graph now starts at what you before considered the end and goes TOWARD the y-axis.  Good luck :)

example 1