1. Chemical Reactions and Energy
Chapter 24 Lesson 4
Chemical Reactions and Energy

2. Energy Changes During a chemical reaction… breaking making bonds bonds
energy is used to break bonds
energy is released when new bonds are formed
breaking
bonds
making
bonds

3. Chemical Reactions—Energy Exchanges
Dynamic explosion
example of a rapid chemical reaction.
Chemical reactions
most proceed more slowly, but all chemical reactions release or absorb energy.

4. Chemical Reactions—Energy Exchanges
Heat
Light
Sound
electricity.
Chemical bonds
the source of this energy

5. Chemical Reactions—Energy Exchanges
Energy Required
chemical reactions ~ some chemical bonds in the reactants are broken, which requires energy.
Bond formation
products produced, new bonds must form.
releases energy.

6. More Energy Out Exergonic Reactions
chemical reactions that release energy
less energy is required to break the original bonds than is released when new bonds form.
Light or heat are given off

7. Heat Release Exothermic reaction.
energy given off in a reaction is primarily in the form of heat
burning of wood
explosion of dynamite

8. H2(l) + O2(l)  H2O(g) + energy
Exothermic Reaction
reaction that releases energy
energy released by making new bonds outweighs energy req’d to break old bonds
H2(l) + O2(l)  H2O(g) + energy
reaction that powers the space shuttle lift-off

9. More Energy In Endergonic reactions
chemical reaction requiring more energy to break bonds than is released when new ones are formed
energy absorbed can be in the form of light, heat or electricity
heat must be added.

10. Heat Absorption Endothermic reaction
energy needed is in the form of heat
some can cause water to freeze.
barium hydroxide (BaOH)2 and ammonium chloride (NH4Cl) in water.

11. 2Al2O3 + energy  4Al + 3O2 Endothermic Reaction
reaction that absorbs energy
energy req’d to break old bonds outweighs energy released by making new bonds
2Al2O3 + energy  4Al + 3O2
process used to obtain aluminum from aluminum ore

12. Catalysts and Inhibitors
A catalyst
substance that speeds up a chemical reaction without being permanently changed itself
the mass of the product that is formed remains the same, but it will form more rapidly.

13. Catalysts and Inhibitors
are used to slow down a chemical reaction
Catalysts and inhibitors
do not change the amount of product produced
only change the rate of production.