Energy And Chemical Reactions

Chemical Reactions: Exothermic & Endothermic

(Energy & Chemical Reactions) Energy Changes ■ Exothermic Reactions ■ Endothermic Reactions ■

A. Energy Changes ■ During

a chemical reaction… • energy is used to break bonds • energy is released when new bonds are formed breaking bonds

making bonds

B. Exothermic Reaction ■ reaction

that releases energy

■ energy

released by making new bonds outweighs energy required to break old bonds

H2(l) + O2(l) → H2O(g) + energy • reaction that powers the space shuttle lift-off

Exothermic process: a change (e.g. a chemical reaction) that releases heat. Burning fossil fuels is an exothermic reaction

C. Endothermic Reaction ■ reaction

that absorbs energy

■ energy

required to break old bonds outweighs energy released by making new bonds

2Al2O3 + energy → 4Al + 3O2 • process used to obtain

aluminum from aluminum ore

■ Endothermic

process: a change (e.g. a chemical reaction) that requires (or absorbs) heat.

Measuring Heat

reaction

reaction

Exothermic reaction, heat given off & temperature of water rises

Endothermic reaction, heat taken in & temperature of water drops

■ Lets

Practice with a Lab!!!