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SURVEY OF CHEMISTRY I
CHEM 1151
CHAPTER 5
DR. AUGUSTINE OFORI AGYEMAN
Assistant professor of chemistry
Department of natural sciences
Clayton state university
CHAPTER 5
CHEMICAL REACTIONS
STOICHIOMETRY
- The area of study involved with calculation of the quantities of
substances consumed or produced in a chemical reaction
- Chemical reactions are represented by chemical equations
- Reactants are substances that are consumed
- Products are substances that are formed
CHEMICAL EQUATIONS
- Reactants are written on the left side of a chemical
equation and products on the right side
- An arrow pointing towards the products, is used to
separate the reactants from the products
- The plus sign (+) is used to separate different reactants
or different products
CHEMICAL EQUATIONS
- Chemical equations must be consistent with
experimental facts
(reactants and products in a reaction that actually takes place)
- Chemical equations must be balanced
(equal numbers of atoms of each kind on both sides)
(Daltons atomic theory)
CHEMICAL EQUATIONS
States of reactants and products
Physical states of reactants and products are represented by:
(g): gas
(l): liquid
(s): solid
(aq): aqueous or water solution
C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(g)
BALANCING CHEMICAL EQUATIONS
- Whole numbers are placed on the left side of the formula (called
coefficients) to balance the equation (subscripts remain unchanged)
- The coefficients in a chemical equation are the smallest set
of whole numbers that balance the equation
C2H5OH(l) + O2(g)
2 C atoms
→ 2CO2(g) + H2O(g)
2 C atoms
Place the coefficient 2 in front of CO2 to balance C atoms
BALANCING CHEMICAL EQUATIONS
- Whole numbers are placed on the left side of the formula (called
coefficients) to balance the equation (subscripts remain unchanged)
- The coefficients in a chemical equation are the smallest set
of whole numbers that balance the equation
C2H5OH(l) + O2(g) → 2CO2(g) + 3H2O(g)
3(1x2)=6 H atoms
(5+1)=6 H atoms
Place 3 in front of H2O to balance H atoms
BALANCING CHEMICAL EQUATIONS
- Whole numbers are placed on the left side of the formula (called
coefficients) to balance the equation (subscripts remain unchanged)
- The coefficients in a chemical equation are the smallest set
of whole numbers that balance the equation
C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(g)
1+(3x2)=7 O atoms
(2x2)+3=7 O atoms
Place 3 in front of O2 to balance O atoms
BALANCING CHEMICAL EQUATIONS
- Whole numbers are placed on the left side of the formula (called
coefficients) to balance the equation (subscripts remain unchanged)
- The coefficients in a chemical equation are the smallest set
of whole numbers that balance the equation
C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(g)
2 C atoms
2 C atoms
(5+1)=6 H atoms
(3x2)=6 H atoms
1+(3x2)=7 O atoms
(2x2)+3=7 O atoms
- Check to make sure equation is balanced
- When the coefficient is 1, it is not written
BALANCING CHEMICAL EQUATIONS
Balance the following chemical equations
Fe(s) + O2(g) → Fe2O3(s)
C12H22O11(s) + O2(g) → CO2(g) + H2O(g)
(NH4)2Cr2O7(s) → Cr2O3(s) + N2(g) + H2O(g)
TYPES OF CHEMICAL REACTIONS
Five Types of Chemical Reactions
- Combination reaction
- Decomposition reaction
- Single-replacement reaction
- Double-replacement reaction
- Combustion reaction
COMBINATION REACTION
- Addition or synthesis reaction
- Two or more reactants produce a single product
X + Y → XY
N2(g) + 3H2(g) → 2NH3(g)
2Mg(s) + O2(g) → 2MgO(s)
SO3(g) + H2O(l) → H2SO4(aq)
DECOMPOSITION REACTION
- Two or more products are formed from a single reactant
XY → X + Y
2H2O(l) → 2H2(g) + O2(g)
2NaN3(s) → 2Na(s) + 3N2(g)
BaCO3(s) → BaO(s) + CO2(g)
SINGLE-REPLACEMENT REACTION
- Substitution or Displacement reaction
- An atom or molecule replaces another atom or molecule
A + BY → B + AY
Fe(s) + CuSO4(aq)
→ Cu(s) + FeSO4(aq)
Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g)
Cl2(g) + 2NaBr(aq) → 2NaCl(aq) + Br2(g)
- Metal replaces metal and nonmetal replaces nonmetal
- Cation replaces cation and anion replaces anion
DOUPLE-REPLACEMENT REACTION
- Exchange or metathesis (transpose) reaction
- Parts of two compounds switch places to form two new compounds
AX + BY → AY + BX
AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq)
BaCl2(aq) + Na2SO4(aq) → BaSO4(s) + 2NaCl(aq)
CaCl2(aq) + Na2CO3(aq) → CaCO3(s) + 2NaCl(aq)
COMBUSTION REACTION
- Reaction between a substance and oxygen (air) accompanied
by the production of heat and light
- A common synonym for combustion is burn
CH4(g) + 2O2(g) → CO2(g) + 2H2O(g) + heat
2CH3OH + 3O2(g) → 2CO2(g) + 4H2O(g) + heat
2Mg(s) + O2(g) → 2MgO(s) + heat
Hydrocarbons are the most common type of compounds that undergo
combustion producing CO2 and H2O
OXIDATION-REDUCTION REACTIONS
- Also called redox reactions
- Involve transfer of electrons
Oxidation - loss of electrons
Reduction - gain of electrons
Ionic solid sodium chloride (Na+ and Cl- ions) formed from solid
sodium and chlorine gas
2Na(s) + Cl2(g) → 2NaCl(s)
The oxidation (rusting) of iron by reaction with moist air
4Fe(s) + 3O2(g) → 2Fe2O3(s)
NONREDOX REACTIONS
- There is no transfer of electrons from one reactant
to another reactant
BaCO3(s) → BaO(s) + CO2(g)
- Double replacement reactions
- Most reactions we have already come across
OXIDATION NUMBER (STATE)
The concept of oxidation number
- provides a way to keep track of electrons in redox reactions
- not necessarily ionic charges
Conventionally
- actual charges on ions are written as n+ or n- oxidation numbers are written as +n or -n
Oxidation - increase in oxidation number (loss of electrons)
Reduction - decrease in oxidation number (gain of electrons)
OXIDATION NUMBERS
1. Oxidation number of uncombined elements = 0
Na(s), O2(g), H2(g), Hg(l)
2. Oxidation number of a monatomic ion = charge
Na+ = +1, Cl- = -1, Ca2+ = +2, Al3+ = +3
3. Oxygen is usually assigned -2
H2O, CO2, SO2, SO3
Exceptions: H2O2 (oxygen = -1)
OF2 (oxygen = +2)
OXIDATION NUMBERS
4. Hydrogen is usually assigned +1 (-1 when bonded to metals)
+1: HCl, NH3, H2O
-1: CaH2, NaH
5. Halogens are usually assigned -1 (F, Cl, Br, I)
Exceptions: when Cl, Br, and I are bonded to oxygen
Cl2O: Cl
+1
O
-2
Cl
+1
6. The sum of oxidation numbers for
- neutral compound = 0
- polyatomic ion = charge
H2O = 0, CO32- = -2, NH4+ = +1
OXIDATION NUMBERS
CO2
The oxidation state of oxygen is -2
CO2 has no charge
The sum of oxidation states of carbon and oxygen = 0
1 carbon atom and 2 oxygen atoms
1(x) + 2(-2) = 0
x = +4
CO2
x
-2 for each oxygen
OXIDATION NUMBERS
CH4
x
+1
1(x) + 4(+1) = 0
x = -4
OXIDATION NUMBERS
NO3x
-2
1(x) + 3(-2) = -1
x = +5
OXIDATION NUMBERS
CH4(g) + 2O2(g)
-4
+1
→
0
CO2(g) + 2H2O(g)
+4
-2
+1
-2
8e- gain
0
CH4(g) + 2O2(g)
-4
→
-2
-2
CO2(g) + 2H2O(g)
+4
8e- loss
+1
+1
OXIDATION NUMBERS
Redox reactions are characterized by transfer of electrons
Oxidation
Reduction
Loss of electrons
Increase in oxidation number
Gain of electrons
Decrease in oxidation number
Reducing Agent (electron donor) Oxidizing Agent (electron acceptor)
Mnemonic
OIL RIG
Oxidation Involves Loss; Reduction Involves Gain
COLLISION THEORY
- Conditions necessary for a chemical reaction to occur
Molecular Collisions
- Reactant particles must collide (interact) with one another
Activation Energy
- The colliding particles must possess a certain minimum amount
of total energy, known as the activation energy
Collision Orientation
- The particles must collide in a proper orientation
(exceptions: single atoms, small and symmetrical molecules)
IONIC EQUATIONS
- When all soluble strong electrolytes are shown as ions
- Chemical equation is balanced
- Soluble compounds (aq) are separated into ions
(only strong electrolytes)
- Insoluble compounds (s), liquids (l), and gases (g)
are NOT separated into ions
IONIC EQUATIONS
Complete ionic equation
- When all ions in both reactants and products are shown
AgNO3(aq) + KCl(aq) → AgCl(s) + KNO3(aq)
Ag+(aq) + NO3-(aq) + K+(aq) + Cl-(aq)
→
AgCl(s) + K+(aq) + NO3-(aq)
IONIC EQUATIONS
Net Ionic Equation
- When spectator ions are cancelled from the complete ionic equation
- Net charge on reactant side must equal net charge on product side
Ag+(aq) + NO3-(aq) + K+(aq) + Cl-(aq)
→
AgCl(s) + K+(aq) + NO3-(aq)
Ag+(aq) + Cl-(aq) → AgCl(s)
- Some ions appear on both reactant and product sides
- These ions play no direct role in the reaction
- These ions are called spectator ions
IONIC EQUATIONS
Neutralization Reaction
HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)
Complete Ionic Equation
H+(aq) + Cl-(aq) + Na+(aq) + OH-(aq)
→
Na+(aq) + Cl-(aq) + H2O(l)
Net Ionic Equation
H+(aq) + OH-(aq) → H2O(l)
EXOTHERMIC REACTION
- Reaction in which heat energy is released (exo- means ‘out of’)
- Heat energy is one of the products of the reaction
- Energy required to break bonds in reactants is less than energy
released by bond formation in products
- Combustion of gasoline
CH4(g) + 2O2(g) → CO2(g) + 2H2O(l) + heat
ENDOTHERMIC REACTION
- Reaction in which heat energy is absorbed (endo- means ‘into’)
- Heat energy is one of the reactants of the reaction
- Energy required to break bonds in reactants is more than energy
released by bond formation in products
- Melting of ice (reason why it feels cold)
- Photosynthesis in plants
N2(g) + O2(g) + heat → 2NO(g)
CHEMICAL EQUATIONS
(STOICHIOMETRIC CALCULATIONS)
Given:
C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(g)
- 1 molecule of C3H8 reacts with 5 molecules of O2 to produce
3 molecules of CO2 and 4 molecules of H2O
- 1 mole of C3H8 reacts with 5 moles of O2 to produce
3 moles of CO2 and 4 moles of H2O
CHEMICAL EQUATIONS
(STOICHIOMETRIC CALCULATIONS)
Given:
C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(g)
What mass of oxygen will react with 96.1 g of propane?
- make sure the equation is balanced
- calculate moles of propane from given mass and molar mass
- determine moles of oxygen from mole ratio (stoichiometry)
- calculate mass of oxygen
1 mol C 3 H 8
5 mol O 2
32.00 g O 2
96.1 g C 3 H 8 x
x
x
44.11 g C 3 H 8 1 mol C 3 H 8
1 mol O 2
= 349 g O2
CHEMICAL EQUATIONS
(STOICHIOMETRIC CALCULATIONS)
Given:
C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(g)
What mass of CO2 will be produced from 96.1 g of propane?
- make sure the equation is balanced
- calculate moles of propane from given mass and molar mass
- determine moles of CO2 from mole ratio (stoichiometry)
- calculate mass of CO2
1 mol C 3 H 8
3 mol CO2 44.01 g CO2
96.1 g C 3 H 8 x
x
x
44.11 g C 3 H 8 1 mol C 3 H 8 1 mol CO2
= 288 g CO2
LIMITING REACTANT
- Also called limiting reagent
- The reactant that is completely consumed in a reaction
- The reactant(s) with leftovers is (are) known as the excess
reactant(s) or excess reagent(s)
To determine the limiting reactant:
- Write and balance the equation for the reaction
- Use given amount of each reactant to determine amount of desired product
- The reactant that gives the smallest amount of product is the limiting
LIMITING REACTANT
Consider the following reaction for producing nitrogen gas
from gaseous ammonia and solid copper(II) oxide:
2NH3(g) + 3CuO(s) → N2(g) + 3Cu(s) + 3H2O(g)
If a sample containing 18.1 g of NH3 is reacted with 90.4 g of
CuO, which is the limiting reactant?
LIMITING REACTANT
2NH3(g) + 3CuO(s) → N2(g) + 3Cu(s) + 3H2O(g)
- Make sure the equation is balanced
- Calculate moles of desired product from each reactant
1 mol NH3
1 mol N 2
18.1 g NH3 x
x
 0.530 mol N 2
17.03 g NH3 2 mol NH3
90.4 g CuO x
1 mol CuO
1 mol N 2
x
 0.380 mol N 2
79.55 g CuO 3 mol CuO
CuO is limiting since it produces smaller amount of N2
PERCENT YIELD
actual yield
Percent yield 
x 100 %
theoretica l yield
Theoretical Yield
The calculated quantity of product formed,
assuming all of the limiting reactant is used up
Actual Yield
The amount of product actually obtained in a
reaction (always less than the theoretical yield)
PERCENT YIELD
Given actual yield:
- Determine the limiting reactant
- Calculate the theoretical yield from the limiting reactant
- Calculate percent yield
PERCENT YIELD
Calculate the percent yield of N2 from the previous example
if 9.04 g of N2 is actually produced
2NH3(g) + 3CuO(s) → N2(g) + 3Cu(s) + 3H2O(g)
- CuO is the limiting reactant
- Calculate the theoretical yield
90.4 g CuO x
1 mol CuO
1 mol N 2
28.02 g N 2
x
x
 10.6 g N 2
79.55 g CuO 3 mol CuO
1 mol N 2
Percent yield 
actual yield
9.04 g N 2
x 100 % 
x 100 %  85.3 %
theoretica l yield
10.6 g N 2