3.6 Chemical Equation Meaning

8/13/2019 3.6 Chemical Equation Meaning

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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:



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STEP 3:

KI (aq)+ Pb(NO3)2(aq) PbI2 (s) + KNO3 (aq)
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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:


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


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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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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3.6 Chemical Equation Meaning