Chemical Reactions
• Occur when atoms rearrange – break
apart and recombine differently
• Produces new substances
• Same as a chemical change
• Energy is absorbed or released
Evidence of a Rxn
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Temperature change
Heat or light
Color change
Odor
Gas bubbles
Appearance of a solid
Rxn Details
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Reactants = they react / on left side
Products = they’re produced / on right side
Arrow = yields (new products are formed)
+ = separates reactants &/or products
s, g, l, aq = indicates state (or solution)
Ways to Show a Rxn
• Word equations:
iron(s) + chlorine(g)  iron (III) chloride(s)
• Skeleton equations:
Fe(s) + Cl2(g)  FeCl3(s)
• Balanced chemical equations:
2Fe(s) + 3Cl2 (g)  2FeCl3(s)
3 Rules of Word Equations
1. Pure metals (only 1 kind of atom) – will be
monoatomic
Ex: iron metal = Fe
2. Pure nonmetals or hydrogen (only 1 kind of atom)
– will usually be a gas & will be diatomic unless
told otherwise
Ex: hydrogen gas = H2
3 Rules of Word Equations
3. Compounds (more than 1 kind of atom):
A. Will reveal the name Ex: carbon dioxide = CO2
B. Use oxidation numbers to find the correct formula (criss
cross & reduce)
Ex: magnesium chloride = Mg+2 & Cl-1, so MgCl2
Try It
• Write a skeleton equation for these:
a. solid barium and oxygen gas react to
produce solid barium oxide
b. solid iron and aqueous hydrogen sulfate
react to produce aqueous iron (III) sulfate
and hydrogen gas
c. calcium carbonate decomposes to
produce calcium oxide and carbon dioxide
Solutions
a. Ba(s) + O2(g)  BaO(s)
b. Fe(s) + HSO4(aq)  Fe(SO4)3(aq) + H2(g)
c. CaCO3(s)  CaO(s) + CO2(g)
Chemical Equations
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Indicates identities of products & reactants
Indicates relative amounts
Must be balanced (law of conservation of mass)
Balanced with coefficients only
Steps to balance:
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Write skeleton (or this will be given to you)
Atom inventory
Guess & check with coefficients
Double check for lowest ratio & equal #
Try It
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Decide if the following equations are
balanced. If not, balance them.
a. 2Al + 6HCl  3AlCl3 + 3H2
b. C5H12 +11O2  5CO2 + 12H2O
c. Ba(ClO3) 2  BaCl2 + 2O2
Solutions
a. 2Al + 6HCl  2AlCl3 + 3H2
b. C5H12 +8O2  5CO2 + 6H2O
c. Ba(ClO3) 2  BaCl2 + 3O2