Today’s Agenda….

• Bellringer: Explain why melting silver is a physical change. Give as much evidence as possible.

• Discuss tests• Discuss assignments• Notes on Chemical Reactions

State Changes

• Physical change• The substance remains the same • It can be reversed• Moo Glue? A state change?– It is not a state change because you are putting

two liquids together and they react to form a solid– The solid is a new substance– This cannot be easily reversed

Review

• What is a chemical change?– Creates a new substance– Not easily reversed

• What are some clues that a chemical change has taken place?– Change in color, odor, sound– Release or absorb heat or light– Produce a gas or solid

Chemical Reactions

• When you observe a chemical change, a chemical reaction has taken place

• Let’s look at some examples!• Create an input/output chart!

Iron Rusting

• Look at the before (right) and after (left).

• Why does the balloon look the way it does?

• What has happened?

Baking Soda and Vinegar

• Think about the before and after.• Why did the balloon look the way it did?• What has happened?

Roasting a Marshmallow

An Apple Rotting

Baking Bread

Why is this not just a change of state?

What do these all have in common?

• Law of conservation of mass• During a chemical OR physical change matter

cannot be created or destroyed.

Law of Conservation of Mass

• Chemical reactions are represented by symbols and formulas• The symbols come from the periodic table• The numbers tell you how many particles are in the

substances• Examples:

– O2

– H20– 3CaCl– 2CO2

– If there is a large number in front you must multiply the small number by that one!

Law of Conservation of Mass

• In a chemical reaction you have products (what you start with) and reactants (what you end up with).

• Reactants are on the right, products are on the left

• The mass must be the same on both sides• The number and type of particles must be the

same on both sides

Law of Conservation of Mass

• If my reactants have a mass of 45 grams, what will the mass of my products be?

• If I have 10 particles that make up my reactants, how many particles will make up my products?

Example:

• Iron Rusting• 4Fe + 3O2 2Fe2O3

• None of the particles are lost, they are just rearranged to form new substances!

Energy in Chemical Reactions

• Every chemical reaction involves a change of energy– Release energy or absorb energy– This energy is usually in the form of heat

• If it releases energy it is called an exothermic reaction– A candle burning

Energy in Chemical Reactions

• If it absorbs energy it is called an endothermic reaction– Baking a cake– An emergency ice pack