Energy in Reactions
Animals eat plants (or other animals that ate
plants) but plants make their own food, glucose.
Chemical Reactions: Energy
This process is called photosynthesis and it
follows this chemical equation:
6CO2 + 6H2O → C6H12O6 + 6O2
Energy in Reactions
6CO2 + 6H2O → C6H12O6 + 6O2
This equation shows us that plants require
carbon dioxide and water in order to produce
sugar.
What else do plants need?
Energy in Reactions
We can rewrite the equation for photosynthesis
to show that it requires energy to occur.
6CO2 + 6H2O + energy(sunlight) → C6H12O6 + 6O2
Energy is listed as a reactant because it “goes
into” the reaction.
What does the sunlight provide to the plants?
Energy in Reactions
When glucose is used as fuel in our bodies the
opposite chemical reaction occurs.
C6H12O6 + 6O2 → 6CO2 + 6H2O + energy
We take glucose and oxygen and produce CO2
and water.
Energy is another (more important) product.
Energy in Reactions
Photosynthesis is an example of an endothermic
reaction.
Endothermic reactions require energy, usually in
the form of heat.
Energy is a reactant in an endothermic reaction.
An endothermic reaction that absorbs heat will
feel cold.
Energy in Reactions
Cellular respiration, the opposite of
photosynthesis, is an example of an exothermic
reaction.
An exothermic reaction releases energy, usually
as heat.
Energy is a product of an exothermic reaction.
Exothermic reactions that release heat will feel
warm or hot.
Energy in Reactions
Endothermic reactions store energy in new
chemical bonds.
Exothermic reactions release energy that was
stored in bonds by breaking them.
Energy in Reactions
Where does the energy that an endothermic
reaction uses go?
Where does the energy that an exothermic
reaction releases come from?