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Questions Notes
Writing & Balancing Chemical
Equations
What are chemical
reactions?
Chemical Reactions
•when substances
undergo chemical
changes to form
new substances
•bonds break,
atoms are
rearranged and
new bonds form
What are the signs
of a chemical
reaction?
Signs of Chemical Reactions
1. energy released or absorbed as
heat or light
2. production of a gas
3. formation of a precipitate.
•A solid that is produced as a result of
a chemical reaction in solution and
that separates from the solution is
known as a precipitate.
4. color change
How are chemical
reactions
represented?
Chemical Reactions
A chemical equation represents the
identities and amounts of the reactants
and products in a chemical reaction.
word equation: the reactant ammonium
dichromate yields the products nitrogen,
chromium(III) oxide and water vapor
formula equation:
(NH4)2Cr2O7(s) → N2(g) + Cr2O3(s) + 4H2O(g)
Chemical Reactions
Reactants – substances that go
through the chemical change
(starting parts)
Product – a substance that is
the result of a chemical change
(ending parts)
Symbols Used in Chemical
Equations
How are chemical
equations written?
Writing Chemical Equations
1. Identify reactants & products
2. Translate the compound
names into formulas
3. Place the reactants’ formulas
on the left separated with +
4. Add the → or ↔ after the
reactants
Writing Chemical Equations
5. Place the products’ formulas
on the right separated with +
6. Add the symbols for state of
matter (s) (l) (aq) (g)
7. Add the ↑ for gas production
or ↓ for precipitate products
Watch this video lesson on writing
compound formulas from names.
Writing Chemical Formulas
http://www.youtube.com/watch?v=i3M-DXJkCVQ
Watch this video lesson on writing
chemical equations.
Reaction Equations
http://www.youtube.com/watch?v=bRmnrAwQztY
How are chemical
equations
balanced?
Balancing Equations
Because of the law of conservation of
mass the number of reactant atoms
must equal the number of product
atoms.
H2 + O2 → H2O
•This equation must be balanced by
inserting coefficients in front of
molecules.
2H2 + O2 → 2H2O
Balancing Chemical Equations
1. Write the formula equation for a
reaction.
2. Draw boxes around each
compound.
3. Make an element inventory.
4. Add coefficients in front of the
boxes until the elements
balance.
Watch this video lesson on
balancing chemical equations.
Balancing Equations
http://www.youtube.com/watch?v=bWQu1xSPJ74
Chemical Equations Review
Key Ideas
• Chemical reactions bond
& unbond atoms to form
new compounds.
• Reactions can be
described with word or
formula reactions.
• All reaction equations
must be balanced by
placing coefficients in
front of formulas.
Key Terms
reactant
product
aqueous
precipitate
coefficient
catalyst
electrolysis