Chapter 24 Lesson 4

Chemical Reactions and Energy

Energy Changes

During a chemical reaction… energy is used to break bonds energy is released when new bonds

are formed

breakingbonds

makingbonds

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.

Chemical Reactions—Energy Exchanges

Energy Heat Light Sound electricity.

Chemical bonds the source of this energy

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.

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

Heat Release

Exothermic reaction. energy given off in a

reaction is primarily in the form of heat

burning of wood explosion of dynamite

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

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.

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.

Endothermic Reaction

reaction that absorbs energy

energy req’d to break old bonds outweighs energy released by making new bonds

process used to obtain aluminum from aluminum ore

2Al2O3 + energy 4Al + 3O2

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.

Catalysts and Inhibitors

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.