SURVEY OF CHEMISTRY I

CHEM 1151

CHAPTER 5

DR. AUGUSTINE OFORI AGYEMANAssistant professor of chemistryDepartment 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 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

C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(g)

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

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) + H2O(g)

2 C atoms 2 C atoms

Place the coefficient 2 in front of CO2 to balance C atoms

BALANCING CHEMICAL EQUATIONS

C2H5OH(l) + O2(g) → 2CO2(g) + 3H2O(g)

(5+1)=6 H atoms 3(1x2)=6 H atoms

Place 3 in front of H2O to balance H atoms

- 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

BALANCING CHEMICAL EQUATIONS

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

- 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

BALANCING CHEMICAL EQUATIONS

C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(g)

2 C atoms(5+1)=6 H atoms

1+(3x2)=7 O atoms

2 C atoms(3x2)=6 H atoms

(2x2)+3=7 O atoms

- Check to make sure equation is balanced- When the coefficient is 1, it is not written

- 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

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)

BALANCING CHEMICAL EQUATIONS

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)

BaCO3(s) → BaO(s) + CO2(g)

2NaN3(s) → 2Na(s) + 3N2(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

- Also called redox reactions- Involve transfer of electrons

Oxidation - loss of electronsReduction - gain of electrons

Ionic solid sodium chloride (Na+ and Cl- ions) formed from solidsodium and chlorine gas

2Na(s) + Cl2(g) → 2NaCl(s)

The oxidation (rusting) of iron by reaction with moist air4Fe(s) + 3O2(g) → 2Fe2O3(s)

OXIDATION-REDUCTION 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

NONREDOX REACTIONS

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 = chargeNa+ = +1, Cl- = -1, Ca2+ = +2, Al3+ = +3

3. Oxygen is usually assigned -2H2O, CO2, SO2, SO3

Exceptions: H2O2 (oxygen = -1) OF2 (oxygen = +2)

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 O Cl

6. The sum of oxidation numbers for - neutral compound = 0- polyatomic ion = chargeH2O = 0, CO3

2- = -2, NH4+ = +1

+1 -2 +1

OXIDATION NUMBERS

CO2

The oxidation state of oxygen is -2 CO2 has no charge

The sum of oxidation states of carbon and oxygen = 01 carbon atom and 2 oxygen atoms

1(x) + 2(-2) = 0x = +4

CO2

x -2 for each oxygen

OXIDATION NUMBERS

CH4

x +1

1(x) + 4(+1) = 0x = -4

OXIDATION NUMBERS

NO3-

x -2

1(x) + 3(-2) = -1x = +5

OXIDATION NUMBERS

CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)

+1-4 +4 +10 -2 -2

CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)

-4

+1 +1

+48e- loss

-2 -20

8e- gain

OXIDATION NUMBERS

Oxidation

Loss of electronsIncrease in oxidation number

Reducing Agent (electron donor)

Reduction

Gain of electronsDecrease in oxidation number

Oxidizing Agent (electron acceptor)

MnemonicOIL RIG

Oxidation Involves Loss; Reduction Involves Gain

Redox reactions are characterized by transfer of electrons

OXIDATION NUMBERS

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)

- 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 EquationH+(aq) + Cl-(aq) + Na+(aq) + OH-(aq)

→ Na+(aq) + Cl-(aq) + H2O(l)

Net Ionic EquationH+(aq) + OH-(aq) → H2O(l)

IONIC EQUATIONS

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

- 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

= 349 g O2

CHEMICAL EQUATIONS(STOICHIOMETRIC CALCULATIONS)

2

2

83

2

83

8383 Omol1

Og32.00x

HCmol1

Omol5x

HCg44.11

HCmol1xHCg96.1

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 CO2 from mole ratio (stoichiometry)

- calculate mass of CO2

= 288 g CO2

CHEMICAL EQUATIONS(STOICHIOMETRIC CALCULATIONS)

2

2

83

2

83

8383 COmol1

COg44.01x

HCmol1

COmol3x

HCg44.11

HCmol1xHCg96.1

Given: C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(g)

What mass of CO2 will be produced from 96.1 g of propane?

- 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:

LIMITING REACTANT

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?

- Make sure the equation is balanced- Calculate moles of desired product from each reactant

LIMITING REACTANT

2NH3(g) + 3CuO(s) → N2(g) + 3Cu(s) + 3H2O(g)

23

2

3

33 Nmol0.530

NHmol2

Nmol1x

NH g 17.03

NHmol1xNHg18.1

22 Nmol0.380

CuOmol3

Nmol1x

CuO g 79.55

CuOmol1xCuOg90.4

CuO is limiting since it produces smaller amount of N2

PERCENT YIELD

%100xyieldltheoretica

yieldactualyieldPercent

Theoretical YieldThe calculated quantity of product formed,

assuming all of the limiting reactant is used up

Actual YieldThe 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

- CuO is the limiting reactant

- Calculate the theoretical yield

2NH3(g) + 3CuO(s) → N2(g) + 3Cu(s) + 3H2O(g)

22

22 Ng10.6Nmol1

Ng28.02x

CuOmol3

Nmol1x

CuO g 79.55

CuOmol1xCuOg90.4

%85.3%100xNg10.6

Ng9.04%100x

yieldltheoretica

yieldactualyieldPercent

2

2