Transcript Chemical Reactions PowerPoint

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
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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!!
Chemical Equations
• 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
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
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