Energy Changes in Reactions

Physical ScienceDecember 7, 2011

Ms CilliPages 206-209

Objectives• Describe the energy changes that take

place during chemical reactions. • Classify chemical reactions as

exothermic or endothermic. • Explain how energy is conserved during

chemical reactions.

What type of reaction is this? C3H8 + 5O2 3CO2 + 4H2O

What is chemical energy?

• Chemical Energy:

• Chemical reactions involve the ________ of bonds in the reactants and the ________ of bonds in the products.

Energy in or out?

Breaking bonds Forming Bonds

Bonds, Chemical Bonds

Remember Phase Changes?!?!

Is heat lost or gained?

1. A plastic bottle of water is placed in a freezer. After several hours, the water has frozen solid.

2. A chef places a stick of solid butter in a saucepan, and heats the saucepan over low heat on a stove. After several minutes, the stick of butter has melted.

Will you either come in or go out?

Exothermic:

Endothermic:

Is heat lost or gained? Exothermic or Endothermic?

1. A plastic bottle of water is placed in a freezer. After several hours, the water has frozen solid.

2. A chef places a stick of solid butter in a saucepan, and heats the saucepan over low heat on a stove. After several minutes, the stick of butter has melted.

Exothermic reaction

Exothermic Reaction Example

Heat is on the _____ side

Endothermic reaction

Endothermic Reaction Example

Heat is on the _____ side

All together now

Tale of Two ReactionsIs it endothermic or exothermic?

(Look and ask yourself what side the heat is on)

C3H8 + 5O2 3CO2 + 4H2O + 2220kJ

2HgO + 181.7 kJ 2Hg + O2

Closure…one step closer

Which one is not one of the 5 types of chemical reactions?

a. synthesis b. decompositionc. single-replacementd. double-replacemente. All of these are chemical reactions

ASSIGNMENT:• Independent Practice:

– Read section 7.3– Work on the study guide

• Homework:– Complete the section 7.3 HW– Due Thursday, December 8 by 8PM