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14.1 Chemical Reactions
Chemical Reactions
Chemical reaction: the process of breaking chemical
bonds and reforming new bonds to make new
substances
Evidence of Chemical Change
Four indicators of a chemical
change:
1. Formation of new gas
2. Formation of new solid
3. Release energy (heat or light)
4. Color change
Coke and Chlorine
Iodine Clock Reaction
Chameleon Reaction
Reactants and Products
Reactant: starting
substance(s)
Product: new
substance(s) formed
Reaction Symbols
arrow = “to produce”
The small symbols in the parentheses (s, l, g, aq)
indicate the phase of each substance in the reaction.
Symbol
(s)
(l)
(g)
(aq)
Meaning
solid
liquid
gas
aqueous - dissolved in solution
Law of Conservation of Mass
Law of Conservation of Mass:
Mass cannot be created or destroyed, only rearranged.
Law of Conservation of Mass
Mass of reactants = mass of products
Example
 5.0 g of magnesium (Mg) burns in 1.0 g
of oxygen (O2). How many grams of
magnesium oxide (MgO) should be
produced?
Mg + O2  MgO
Check-In
 10.2 g of Lithium Fluoride (LiF) and an
unknown amount of sodium chloride
(NaCl) react to form 13.5 g of Lithium
chloride (LiCl) and 21.2 g of Sodium
fluoride (NaF). How many grams of
sodium chloride reacted?
LiF + NaCl  LiCl + NaF
A Reminder:
Numbers in Chemical Formulas
Balancing Chemical Equations
The law of conservation of mass tells us that atoms and
molecules must be balanced on both sides of a chemical
equation.
Balancing Chemical Equations
coefficient
subscript
Rules:
1. Subscripts (small numbers) CANNOT be changed.
2. Coefficients (big numbers) placed in front of the
chemical formula.
Balancing Chemical Equations
coefficient
subscript
Balancing Steps:
1. Draw a line to separate reactants from products
2. Make a list! – each element on each side
--Write in the same order
3. Add coefficients if needed (change your list!)
Balancing Chemical Equations
___Li2S + ___ Cl2 → ___ LiCl + ___S
Balancing Chemical Equations
___Mg + ___ O2 → ___ MgO
Balancing Chemical Equations
Example #1
___Cu2S + ___ O2 → ___ Cu2O + ___ SO2
Balancing Chemical Equations
Example #2
___ Al + ___ O2 → ___ Al2O3
Balancing Chemical Equations
EXIT SLIP
___ CO2 + ___ H2 → ___ CH4 + ___ H2O
Hints for balancing:
1) Save single elements (Al, Cu, Na)
and diatomic molecules (I2, Cl2, O2)
for last.
C 2H 4 +
O2
→
CO2 +
H2O
Hints for balancing:
2) Find Common Multiples
KClO3
→
KCl +
O2
Hints for balancing:
2) Keep polyatomic ions together
H2SO4 +
Ca3(PO4)2 →
Ca(H2PO4)2 +
CaSO4