Chemical Reactions
Chapter 2
Section 1 & 2
Physical Background• Physical Property: Characteristics of matter
that can be seen through direct observations• Density• Melting point• Boiling Point
• Physical Change: Change in which the identity of the substance does not change
Chemical Background• Chemical Property: characteristics of
matter that can only be observed when one substance changes into a different substance– Iron to Rust
• Chemical Change: New Substance is formed
A Change of Properties• The properties of these substances
are very different from the starting substances
• In a chemical reaction, bonds are broken. Atoms are then rearranged to form new substances
Signs of a Chemical Reaction
• Gas
• Solid
• Energy– Endothermic– Exothermic
• Color change
Chemical or Physical• Glass Breaking
• Hammering wood together
• Burning Leaves
• Melting Ice
• Frying an egg
• Melting butter
• Bleaching your hair
• Fireworks
• Mixing salt with water
Chemical Formula
• A shorthand way to use chemical symbols and numbers to represent a substance
• Shows how many of each atom is present in a molecule
• 3H2O• Subscript 2 – (applies to symbol before it)• Coefficient 3 – (applies to entire
molecule)
Be Accurate Symbols can be mistaken!!
• Use chemical symbols and formulas as a shortcut to describe a chemical reaction
• Reactants = starting material
• Products = substances formed from a reaction
C + O2 CO2
reactants before arrow products after arrow
Chemical Equations
Law of conservation of mass
• During a reaction, mass is neither created nor destroyed
• Equations must be balanced because atoms are neither created nor destroyed
Mass of Reactants = Mass of Products
How to balance an equation
Step 1
Count the number of atoms on each side
Step 2
You can only add or change coefficients to balance the number of atoms on each side.
Chemical Equation
• Shows the reaction between reactants and products
• Reactants-starting material
• Products-what is formed
• C + O2 CO2
• C=1 C=1
• O=2 O=2 http://www.explorelearning.com/index.cfm?method=cResource.dspView&ResourceID=408
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