SCH 3U
Three ways
1.
2.
3.
-
Chemical Reactions
of writing chemical equations:
Word equations
Skeleton equations
Balanced chemical equations
Evidence of a Chemical Reaction
change in colour
- formation of a gas
change in heat/light
- formation of a precepitate
change in odour
Law of Conservation of Mass
In any chemical reaction, the mass of the products is always equal to the
mass of the reactants. Matter can neither be created nor destroyed.
Rules for Balancing Chemical Equations
1. Balance atoms/polyatomic ions left to right. Leave oxygen and hydrogen
until the end.
2. Balance hydrogen and oxygen leaving the one that appears in the most
compounds last.
Classification of Chemical Reactions
1. Synthesis Reactions
E + E  C or
C + C  C or
C+E→C
 element + oxygen  oxide
 eg. C(s) + O2(g)  ____(g)
metal + non-metal  binary compound (salt)
__ Zn(s) + S8(s)  __ ____(s)
2. Decomposition
CE+E
or
C  C + C or
C→C+E
Eg.
H2CO3  H2O + CO2 or __ NaCl  ______________
3. Combustion
Rapid reaction of a substance with oxygen.
 Substances containing carbon and hydrogen (fuels) form carbon
dioxide and water during combustion: C3H8 (g) + O2 (g)  CO2 (g) + H2O(g)
 Incomplete combustion of fuels results in production of carbon
monoxide (poisonous gas) and/or soot (C).
C2H4 (g) + O2 (g)  CO (g) + H2O(g)
4. Single Displacement

A + BC  AC + B
or
AB + C  AC + B
Metal element replaces metal, e.g. Cu + 2AgNO3  ____________
Non-metal element replaces non-metal, eg. Cl2 + 2KBr  ________
1+
 Cation: positive ion, usually a metal or H .
 Anion: negative ion, usually a non-metal.
 The activity series for metals determines whether a reaction
will occur. Li > K > Ca > Na > Mg…Au.
There is a displacement if the metal is higher than the metal ion on
the activity series:
Fe + Hg(NO3)2  ____________ – Fe higher than Hg2+
Zn + MgCl2  ______________ – Zn lower than Mg2+
 There is an activity series for halogens as well: F > Cl > Br > I
5. Double Displacement Reactions
C+C→C+C
 Will form:

AB + CD → AD + CB
a precipitate (solid that is formed)
a gas (decomposition of a product)
salt and water (neutralization reaction)
If both compounds remain in solution than there has been no
reaction.
NaCl(aq) + AgNO3(aq) → _______________________
2 HCl(aq) + MgCO3(s) → _______________________
H2CO3(aq) → H2O(l) + CO2(g)
KOH(aq) + HNO3(aq) → ________________________