CHEMICAL REACTION
Hak Sok Chea
2009 ~2010
Chemical equation
 A chemical change is called a CHEMICAL REACTION
 Writingg chemical equations:
q
H 2 + O2 ⎯⎯
→ H2O
 Balance the above equation
2H 2 + O2 ⎯⎯
→ 2H 2O
 H2 and O2 is referred as Reactant, and WATER is referred
to as Product
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Interpretation of a chemical reaction
→
2 H2O
+ One molecules
→
Two molecules
2 moles
+
1 mole
→
2 moles
2 (2.02) = 4.04 g
+
32.00 g
→
2 (18.02 g) = 36.04 g
2 H2
+
Two molecules
O2
36.04 g of reactants
36.04 g of pproducts
 Reactants are conventionally written to the left and Product
to the right of the arrow:
Reactants
→
Products
 Physical state of Reactants and Products are stated by using
abbreviation:
2CO(g) + O 2 (g) ⎯⎯
→ 2CO 2 (g)
2P(s) + 3Cl2 (g) ⎯⎯
→ 2PCl3 (l)
2HgO(s) ⎯⎯
→ 2Hg(l) + O 2 (g)
 To represent physical process
H 2 O(l) ⎯⎯
→ H 2 O(s)
H 2 O(l) ⎯⎯
→ H 2 O(g)
 To describe process of salt or gas dissolving in water
H2O
NaCl(s) ⎯⎯⎯
→ NaCl(aq)
H2O
HCl(g) ⎯⎯⎯
→ HCl(aq)
2
Balancing Chemical Equations
 Observing a progress of a reaction
 Presence of bubble: ggaseous p
product is formed
 Color change
 Equation balancing steps
 Identify all reactants and products and write their correct formula
on the left and the right side of the equation respectively
 Begin balancing the equation by trying suitable coefficients that will
make the number of atoms of each element the same on both side of
the reaction
 Look for each elements that appear only one on each side of the
equation and with equal numbers of atoms on each side. The
formula containing these elements must have the same coefficient
 Next look for the elements that appear only one on each side of
the equation but in unequal number. Balance these elements
 Finally balance elements that appear in two or more formula on
the same side of the reaction
 Check yyour balance equation
q
to be sure that you
y have the same
total number of each type of atoms on both side of the equation
row
KClO3 ⎯⎯
→ KCl + O 2
 Balance the O atom by placing a 2 in front of KClO3 and a 3 in
front of O2
 Example:
2KClO3 ⎯⎯
→ KCl + 3O 2
 Balance the K and Cl atom by placing a 2 in front of KCl
2KClO3 ⎯⎯
→ 2KCl + 3O 2
3
Some common type of chemical
reactions
 When two elements react: A combination occurs producing
a binary compound
 A metal and nonmetal react: the product is ionic with a
formula determined by the charges on the ions the elements
form
 Two nonmetal react: the product is a molecule with polar
covalent bonds,, with a formula consistent with the normal
valences of the atoms involved
 Some pairs of elements may react only slowly and require
heating for significant reaction to occur
Examples
Ca + O2
Al + I2
H2 + O2
I2 + Cl2
→
→
→
→
CaO (ionic)
AlI3 ((ionic))
H2O (covalent)
ICl, ICl3, or ICl5 (covalent)
The above equation are unbalance
2Ca + O2 →
2Al + 3I2 →
2H2 + O2 →
I2 + (3,5)Cl2 →
2CaO (ionic)
2AlI3 (ionic)
2H2O (covalent)
2ICl, (2)ICl3, or 2ICl5 (covalent)
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 Metal oxide react with water produces a metal hydroxide
→
→
Na2O + H2O
MgO + H2O
2NaOH
Mg(OH)2
 Nonmetal
N
t l oxide
id with
ith water
t produces
d
an oxyacid
id iin which
hi h
the nonmetal is in the same oxidation state as in the oxide
you started with
→
→
SO2 + H2O
Cl2O5 + H2O
H2SO3
2HClO3
 Reaction of a metal oxide with a nonmetal oxide gives an
oxysalt
CaO(s) + SO3(g)
→
CaSO4(s)
 Reaction of a metal hydroxide with a nonmetal oxide produces a
"hydrogen" oxysalt
NaOH(s) + CO2(g)
→
NaHCO3(s)
 Reaction of an acid with a base gives a salt plus water
2HCl(aq) + Ca(OH)2(aq)
→
CaCl2(aq) + 2H2O(l)
3H2SO4(aq) + 2Fe(OH)3(s)
→
Fe2(SO4)3(aq) + 6H2O(l)
 Ammonium salts react with metal hydroxides and oxides in an
acid-base reaction to produce ammonia
NH4Cl(aq) + KOH(aq) → NH3(g) + H2O(l) + KCl(aq)
2NH4NO3(s) + CaO(s) → 2NH3(g) + H2O(l) + Ca(NO3)2(s)
5
 Reaction of the salt of a weak acid with a strong acid produces the weak
acid and a salt
BaCO3(s) + 2HBr(aq)
K2SO3(aq) + 2HNO3(aq)
Ca3(PO4)2(s) + 6HCl(aq)
→ BaBr2(aq) + H2O(l) + CO2(g)
→ 2KNO3(aq) + SO2(g) + H2O(l)
→ 3CaCl2(aq) +2 H3PO4(aq)
 Reaction of solutions of two soluble salts with one another can give a
precipitate of an insoluble salt formed by a double replacement reaction
CaCl2(aq) + K2CO3(aq) → CaCO3(s) + KCl(aq)
AgNO3(aq) + FeCl3(aq) → AgCl(s) + Fe(NO3)3(aq)
But
NiSO4(aq) + MgI2(aq) → no reaction (NiI2 and MgSO4 are both soluble)
Al(NO3)3(aq) + Pb(C2H3O2)2(aq) → no reaction (Al(C2H3O2)3 and Pb(NO3)2
are both soluble)
 Heating an oxysalt produces a metal oxide plus a nonmetal
oxide or a metal salt plus oxygen, or some combination of these
two decomposition reactions
Δ
KClO3((s)) ⎯⎯
( ) + O2(g)
→ KCl(s)
Δ
CaCO3(s) ⎯⎯
→ CaO(s) + CO2(g)
Δ
Pb(NO3)2(s)
PbO(s) + NO(g) + NO2(g) + O2(g)
⎯⎯
→
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