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Tea Bag + Sugar + Hot Water Tea
Tb + S + Hw T
ReactantsProducts
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A chemical equation is a symbolic representation of a
chemical reactionin terms of chemical formulae
Reactants Products
Reactants:Substances that changedProducts:New substances formed
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Chemical Symbol In Chemical Equation
+ react with
reversible
produce/ to giveirreversible
(s) solid
(l) liquid (aq) aqueous
(g) gas
precipitation
gas release combustion/
heating
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1.Definition
2.Balancing Equations
3. Interpret Chemical Equations
Qualitatively
Quantitatively
4.Stoichiometry
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Relationship mole, ionic formula and
balancing in chemical equation
2Na + Cl2 2NaCl 2 mole sodium react with 1 mole chlorine gas produce 2 mole
sodium chlorine
NaCl
Refer to
the number of mole of atoms
by comparing left side and right side
The number of atom should be equal for both side
Sodium chloride Na+ Cl-
Charge +1 -1
Balance charge +1 (1)
= +1
-1(1)
= -1
Ratio 1 1
Ionic formulae NaCl
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Synthesis
Decomposition
Single-replacement
Double-replacement
Combustion
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Two or more substances react to form asingle substance.
Example: 2Na + Cl2 2NaCl
2H2+ O2 2H2O
A + B AB
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A compound breaks downinto two or moresimpler substances.
Example: 2H2O 2H2 + O2
CaCO3 CaO + CO2
AB A + B
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One element takes the placeof another
element in a compound.
Example:
2K + 2H2O H2 + 2KOH
Cu + 2AgNO3 Ca(NO3)2+ CO2
A + BC B + AC
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Two different compounds exchange positive
ionsand form two new compounds.
Example:
Pb(NO3)2+ 2KBr PbBr2 + 2KNO3
CaNO3+ 2HCl CaCl2+ H2CO3
AB + CD AD + CB
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A substance reacts rapidly with oxygen,
often producing heat and light.
Example:
CH4+ O2 CO2+ 2H2O
2H2+ O2 2H2O
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KI + Pb(NO3)2 PbI2+ KNO3
Is it a balanced chemical equation?
Why we need to balance the chemical
equation?
Based on the law of mass conservation
atoms are neither created nor destroyed inchemical reactions.
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Step 1:Determined the chemical formulae of reactants and
products.
Step 2:
Write the unbalanced chemical equation.
Step 3:
Write the symbols that can give the information about the
reactants and products.
Step 4:
Apply an appropriate coefficient in front of each chemical
formula so that the numbers of each elements in both
sides are same.
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Reactants: KI , Pb(NO3)2
Products: PbI2, KNO3
STEP 1:
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STEP 2:
KI + Pb(NO3)2 PbI2+ KNO3
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STEP 3:
KI (aq)+ Pb(NO3)2(aq) PbI2 (s) + KNO3 (aq)
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KI + Pb(NO3)2 PbI2+ KNO3
Element Left Right
K 1 1
I 1 2
Pb 1 1
NO3 2 1
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STEP 4:
Balanced the I:
2KI(aq) + Pb(NO3)2(aq) PbI2(s) + KNO3(aq)
Balanced the K:2KI(aq) + Pb(NO3)2(aq) PbI2(s) + 2KNO3(aq)
Balanced the NO3:2KI(aq) + Pb(NO3)2(aq) PbI2(s) + 2KNO3(aq)
KI (aq) + Pb(NO3)2(aq) PbI2(s) + KNO3(aq)
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2KI(aq) + Pb(NO3)2(aq) PbI2(s) + 2KNO3(aq)
Element Left Right
K 2 2
I 2 2
Pb 1 1
NO3 2 2
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Finally, the balanced chemical equation is:
2KI(aq) + Pb(NO3)2(aq) PbI2(s) + 2KNO3(aq)
Check the answer:
Left Right
K 2 2
I 2 2
Pb 1 1
NO3 2 2
Both sides
have the same
number of each
element
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Qualitatively
2KI(aq) + Pb(NO3)2(aq) PbI2(s) + 2KNO3(aq)
Reactants: aqueous potassium iodide, KI; aqueous
plumbum nitrate, Pb(NO3)2
Products: precipitate of plumbum iodide, PbI2; aqueous
potassium nitrate, KNO3
aqueous potassium iodide, KI reacts with aqueous
plumbum nitrate, Pb(NO3)2to produce precipitate of
plumbum iodide, PbI2and aqueous potassium nitrate, KNO3
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2KI(aq) + Pb(NO3)2(aq) PbI2(s) + 2KNO3(aq)
2 unitsof KI reacts with 1unitof Pb(NO3)2 to yield 1unitof
PbI2and 2 units of KNO3.
2x6.02x1023units of moleculeKI reacts with
1x6.02x1023unit of moleculePb(NO3)2to yield1x6.02x1023unit of moleculePbI2and 2x6.02x10
23units of
molecule KNO3.
2 molof KI reacts with 1 molof Pb(NO3)2to yield 1 molof
PbI2 and 2 molof KNO3.332g unit of KI reacts with 331gunit of Pb(NO3)2to yield
461gunit of PbI2and 202gunit of KNO3.
Quantitatively
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1. What is the name and chemical formulae
of the reactants and products?
2. Write a balanced equation for the
reaction.
Products
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Suggested answers:
1. Reactants: potassium iodide, KI;argentum nitrate, AgNO3
Products: argentum iodide, AgI;
potassium nitrate, KNO3
2. KI(aq) + AgNO3(aq) AgI(s) + KNO3(aq)
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Left Right
K 1 1
I 1 1
Ag 1 1
NO3 1 1
KI(aq) + AgNO3(aq) AgI(s) + KNO3(aq)
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Number of
moles
Mass, g Number of particles
Volume, dm3
(gas phase only)
Molar
mass
Molar
massX X NA
NA
Molar volume of gasX Molar volume of gas
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Example 1:
Zn (s) + 2 HCl (aq) ZnCl2(aq) + H2(g)
From the given equation, calculate thea) number of moles of zinc b) mass of zinc
that react completely with 0.2 mol hydrochloric acid.
[Relative atomic mass: Zn, 65]
Given: Zn (s) + 2 HCl (aq) ZnCl2 (aq) + H2(g)
? mol 0.2 mol
Solution:
From equation: 1 mol 2 mol 1. Compared the
stoichiometry of the equation.
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a) From the equation, 2 mol of hydrochloric acid (HCl) reacts
completely with 1 mol of zinc (Zn).
Therefore, 0.2 mol of HCl reacts completely with
mol zinc
= 0.1 mol zinc
1
2
2.02. Get the number of moles of
Zn that reacted.
b) Mass of zinc that reacted = number of moles X molecular mass
= 0.1 X 65
= 6.5 g
3. Change the unit:
number of moles mass
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Example 2:
Heating of magnesium in oxygen gas produced magnesium
oxide.
a) Write the chemical equation for this reaction.
b) Calculate:
i) the volume of gas oxygen that reacted
ii) number of molecules of magnesium oxide that produced
if 6g of magnesium heating in oxygen gas at STP.
[Relative atomic mass: Mg, 24, O, 16; Avogadro number: 6 x 1023;
1 mole of gas occupies a volume of 22.4 dm3at STP]
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Solution:
a) 2 Mg (s) + O2(g) 2 MgO (s)
b) i) From the equation, 2 mol of Mg reacts with 1mol O2.
mol of Mg reacted =
= = 0.25
thus, 0.25 mol Mg reacts with = 0.125mol O2
volume of gas oxygen that reacted
= number of moles x molar gas volume
= 0.125 x 22.4 dm3
= 2.8 dm3
Mgofmassrelative
Mgofmass
24
6
1. Compared the
stoichiometry of
the equation.
2
25.0
2. Get the numberof moles of Mg that
reacted.
3. Change the unit:
number of moles
volume
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b) ii) from the equation,
2 Mg (s) + O2(g) 2 MgO (s)
2 mol Mg produced 2 mol MgO
Thus, 0.25 mol Mg produced 0.25 mol MgO
Number of molecule MgO that produced
= number of moles x Avogadro number
= 0.25 x 6.02 x 1023
= 1.56 x 1023
1. Compared the
stoichiometry of
the equation.
2. Get the number
of moles of MgO
that produced.
3. Change the unit:
number of moles
Number of particles
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Learning Outcomes:
State the meaning of chemical equation.
Identify the reactants and products of a
chemical equation.
Write and balance chemical equations.
Interpret chemical equations
quantitatively and qualitatively.
Solve numerical problems using
chemical equations.
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