Chapter 14 Section 1

Objectives:

Describe how chemical reactions produce new substances that have different chemical & physical properties

Identify 4 signs that indicate that a chemical reaction might be taking place

Explain what happens to chemical bonds during a chemical reaction

Question of the Day?

What do baking bread, launching a space shuttle, and digesting food have in common?

Chemical Reactions:

A process in which one or more substances change to make one or more new substances

Chemical reactions around you…

Think about the chemical reactions that occur in school everyday….

Make a list

Consider this…

Carbon dioxide (CO2) Dissolved under pressure –

effervescence in carbonated beverages

Does not combust and is denser than air – used in fire extinguishers to smother flames

Dry ice (CO2 in its solid form) – cooling effect – it sublimates!!

Signs of Chemical Reactions: Gas formation (bubbles!)

Solid formation (precipitate)

Energy change (light, thermal, electrical…)

Color change

A Change of Properties:

Signs don’t guarantee that a chemical change has taken place

Formation of NEW substance with DIFFERENT properties is the key!

http://101science.com/images/beaker.gif

Bonds: Holding Molecules Together Chemical bond: force that hold 2

atoms together in a molecule

Chemical reactions require that original bonds are broken and new bonds are formed

http://www.blobs.org/science/chemistry/bond.gif

http://facstaff.gpc.edu/~pgore/PhysicalScience/covalent_bond_animation.gif

Breaking & Making Bonds:

Molecules are always in motion

They may bump into each other

With enough energy, bonds can be broken

Atoms can rearrange, and new bonds form

Molecules in Motion…

http://www.aquamem.com/molecular_modeling/DPB_Reaction_Pages/MCA_DMA986_movie_optimized_v1.gif

New Bonds, New Substances Sodium is a violently reacting metal Chlorine is a poisonous gas

Combined: Sodium chloride (NaCl) – table salt!

Completely harmless together…

Sodium:

The Periodic Table of Videos – University of Nottingham

http://www.periodicvideos.com/videos/011.htm

Chlorine:

The Periodic Table of Videos – University of Nottingham

http://www.periodicvideos.com/videos/017.htm

Reference:

Holt Science and Technology: Physical Science. New York: Henry Holt & Co, 2007. Print.