Changes in Matter
Section 3.2
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Water
• What is water?
• What are some of the physical properties of water?
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Does it have taste?
Color?
Smell?
Temperature?
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Physical Changes
• Matter can exist as solids, liquids, or gases.
• Energy causes phase changes.
• When a substance changes from one phase to another, it
undergoes a physical change.
• Physical change- some of the physical properties of a
substance change, but the identity of the substance remains
the same.
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Mixtures and Solutions
• Sometimes a physical change occurs when substances
combine.
• Mixture-two or more substances that do not combine chemically.
• Atmosphere- mixture of gases but they keep their separate
chemical properties.
• Salt water is a solution.
• Solution- type of mixture in which one substance is evenly mixed
with another substance.
• The taste changes but the physical water and physical salt are not
changed in any way.
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Chemical Changes
• Chemical change- when the substance is turned into many
different substances. (chemical identity is changed)
• A chemical reaction takes place during a chemical change.
• New substances are produced when a chemical reaction
occurs.
• Rust
• Wood Burning
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Chemical Changes vs. Physical Changes
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Chemical Reactions and
Equations
• Chemical Equations- symbols represent elements and
formulas represent compounds.
• Chemical equations contain reactants (raw materials in a
chemical reaction) and products ( substances produced by the
reaction).
• A plus sign in a chemical equation shows that two or more
reactants will combine.
• Reactants are usually on the left side of the equation.
• Products are usually on the right side of the equation.
• The arrow means produces or yields the products. The arrow also
shows the direction of the reaction.
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What have we learned?
• Look at Figure 3.11 on page 60 in your book.
• Name the reactants in this chemical equation.
• Name the products in this chemical reaction.
• How many molecules of carbon dioxide are indicated on the right
of the chemical equation?
• You decide that instead of water today you want to add a
flavor packet to it to make fruit punch. Is this a physical
change or a chemical change?
• When you light a match, is this a physical change or a chemical
change?
• Given the equation 2HCl  H2 + Cl2:
• What are the Reactants?
• What are the Products?
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Balanced Chemical Equations
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H2 + O2  H2O
What’s wrong here?
Atoms do not disappear during during chemical reactions.
Therefore, we need to balance this equation.
• We balance equations by adding coefficients in front.
• Coefficient shows how many molecules or atoms of a substance are
involved in the reaction.
• Number of atoms must be the same on both sides.
• 1st we need to place a coefficient before the product.
• H2 + O2  2H2O
• Now oxygen are balanced but the hydrogen are not.
• 2H2 + O2  2H2O
• Balancing Chemical Equations
What have we learned?
1. Explain how water changes from a solid to a liquid.
1. What are the reactants and products in a chemical
equation?
1. A lump of sugar burns. Is this an example of a physical
change or a chemical change? Explain why.
1. In your own words, describe what the following chemical
reaction for hydrogen peroxide means: H2 + O2  H2O2.
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