Chemical Reactions
Objectives:
1. Write a word equation
2. Write a skeletal equations
3. Describe the parts to a chemical reaction
All Chemical Reactions have 2 Parts
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•
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Reactants—what you start with
Products—what you end with
Reactants turn into products
Reactants Products
Law of Conservation of Mass
• Atoms aren’t created nor destroyed, just
rearranged
• Can be expressed in a few ways:
• Sentence:
– Copper reacts with chlorine to form copper(II)
chloride
• Word equation
– Copper + chlorine  copper(II) chloride
• Skeletal
– Cu + Cl CuCl
Symbols
• Arrow () separates reactants from products
(points to products)
– Read as “reacts to form” or “yields”
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•
•
•
•
•
+-- “and”
(s) after formula—solid
(g) after formula= gas
(l) after formula=liquid
(aq)—dissolved in water—aqueous solution
Double arrow—reversible reaction
Skeletal Equations
• Uses formulas and symbols to describe a
reaction
– Does not indicate how many, they are NOT
balanced
Writing Skeletal Equations
• Solid Iron (III) sulfide reacts with gaseous
hydrogen chloride to form iron (III) chloride
and hydrogen sulfide gas.
Reverse it!
• Fe(s) + O2(g)  Fe2O3(s)
• Cu(s) + AgNO2(aq)  Ag(s) + Cu(NO3)2(aq)
• NO2(g)  N2(g) + O2(g)
Balancing Chemical Equations
• Atoms can’t be created or destroyed
– All the atoms we start with we must end up with
• A balanced equation has the same number of
each element on both sides of the equation
Rules
• Assemble the correct formulas for all the
reactants and products
• Count the number of atoms of each type
appearing on both sides
• Balance the elements one at a time by adding
coefficients (number in the front).
• Balance Hydrogen and Oxygen last!
• Double check
What NOT to do
• Never change a subscript to balance an
equation
• Never put a coefficient in the middle of a
formula
Example
Practice (balance)
Practice (balance and give word
equation)
Give the chemical equation and then
balance
• Zinc and lead (II) nitrate react to form zinc
nitrate and lead.
• Aluminum bromide and chlorine gas react to
form aluminum chloride and bromine gas
• Sodium phosphate and calcium chloride react
to form calcium phosphate and sodium
chloride