The chemical transformation of one substance to another is called a chemical reaction and is written using chemical formulas in what we call a chemical equation.

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http://www.youtube.com/watch?v=uCwHzTsx5yY

Chemical reactions

Al + Br2 AlBr3Chemical equation:

reactants product

Chemical reaction: Aluminum reacts with bromine to produce aluminum bromide.

5. Change in pH (blue red)(red blue)

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Chemical reactions can be observed and /or sensed:

Chemical Equations are Balanced

To balance an equation, numbers called coefficients are used in front of formulas.

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Law of mass conservation: mR = mP

the number atoms in the reactants the number of atoms in the products:

H2 + O2 H2O

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Na3PO4(aq) + MgCl2(aq) NaCl(aq) + Mg3(PO4)2(s)

Balance Polyatomic Ions as a unit

PO4 2 PO4

2Na3PO4(aq) + MgCl2(aq) NaCl(aq) + Mg3(PO4)2(s)

6 Na Na

2Na3PO4(aq) + MgCl2(aq) 6NaCl(aq) + Mg3(PO4)2(s)

Mg 3Mg

2Na3PO4(aq) + 3MgCl2(aq) 6NaCl(aq) + Mg3(PO4)2(s)

6 Cl 6 Cl

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composition decomposition

Double replacement

Single replacement

e + e cmpdAl + Cl2 AlCl3

cmpd e + eH2O H2 + O2

e + cmpd cmpd + eZn + HCL ZnCl2 + H2

cmpd + cmpd cmpd + cmpdHCl + NaOH NaCl + H2O

cmpd cmpd + eKClO3 KCl + O2

cmpd cmpd + cmpdCaCO3 CaO + CO2

Types of reactions

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In a combination reaction, two or more elements (or simple compounds) combine to form one product

2Mg(s) + O2(g) 2MgO(s)

2Na(s) + Cl2(g) 2NaCl(s)

SO3(g) + H2O(l) H2SO4(aq)

A B A B+

In a decomposition reaction, one substance splits into two or more simpler substances.

2HgO(s) 2Hg(l) + O2(g)

2KClO3(s) 2KCl(s) + 3O2(g)

Potassium + oxygen ? (names & formulas & balance)

Water ? Formula(s) , name(s) & balanced equation

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In a single replacement reaction, one element takes the place of a different element in a reacting compound.

Zn(s) + 2HCl(aq) ZnCl2(aq) + H2(g) Fe(s) + CuSO4(aq) FeSO4(aq) + Cu(s)

Mg(s) + H2O (l) ? Formulas , names, & balance

In a double replacement, two elements in the reactants exchange places.

+ - + -

AgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq)

ZnS (s) + 2 HCl(aq) ZnCl2(aq) + H2S(g)

Sodium hydroxide + HCl ? Formula(s) , name(s) & balanced equation

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Oxidation-reduction reactions

An oxidation–reduction reaction transfers electrons from one reactant to another

(OIL)

Reduction: gain e-

(RIG)reduction

oxidation

0

+1

+2

-1-2

Charg

e

incr

ease

s

Charg

e

decre

ase

s

Zn (s) + CuSO4 (aq) Cu (s) + ZnSO4 (aq)

oxidationZn (s) Zn2+(aq) + 2e-

reductionCu2+(aq) + 2e- Cu(s)

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Charges: 0 +2 0 +2

Zn (s) + Cu SO4 (aq) Cu (s) + Zn SO4 (aq)

Sulfate does not change, therefore to simplify:

Who is going up ? Zn oxidation or reduction? oxidation

Who is going down ? Cu oxidation or reduction? reduction

Example

http://youtu.be/OxGjbHzxQSI

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A reduces BA is the Reducing agent

B oxidizes AB is the Oxidizing agent

What is A doing to B?

What is B doing to A?

Mg + HCl MgCl2 + H2

Reducing agent Mg or HClOxidizing agent Mg or HCl

Mg itself is oxidizedH in HCl itself is reduced

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The Mole

When particles get very small, counting them is more difficult and requires that we bundle them. Such is the case with eggs.

The bundle has 12 eggs and it is called a dozen

For very very small particles, such as atoms and molecules, the bundle gets larger.

12 = dozen

Abbreviated mol whether singular or plural.

The number 6.02 x 1023 is called Avogadro’s number

A mole is the amount of substance containing 6.02 x 1023 particles

The Latin word for “bundle”, “heap”, “pile” is mole.

The bundle has 6.02 x 1023 particles and it is called a mole.

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If the substance is an element the particles are atoms1 mole of Na = 6.02 x 1023 Na atoms

If the substance is an covalent compound the particles are molecules

1 mole of H2O = 6.02 x 1023 H2O molecules

If the substance is an ionic compound the particles are formula units

1 mole of NaCl = 6.02 x 1023 NaCl formula units

Equality: 1 mole = 6.02 x 1023 particles

Conversion Factors: 6.02 x 1023 particles and 1 mole 1 mole 6.02 x 1023 particles

Avogadro’s number is used as a conversion factor:

How many moles of CO2 are in 2.50 x 1024 molecules of CO2?

2.50 x 1024 molecules CO2 x 1 mole CO2 = 4.15 moles of CO2

6.02 x 1023 molecules CO2

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Molar Mass

It is easier to weight particles than to count them.

Therefore, we need a conversion factor between moles and grams.

Molar Mass = the mass of one mole of a substance

gramsmolesparticles Avogadro’s

Counting of particles is not practical

? grams1 mole

= the atomic mass of an element expressed in grams

C 12.0 gmole

= the sum of the molar masses of the elements in the formula.

H2O 1.0+1.0+16.0 = 18.0 18.0 g mole

6C

12.01

We use molar masses to the nearest 0.1 g

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Example: Aluminum is often used for the structure of lightweight bicycle frames. How many grams of Al in 3.00 moles of Al?

3.00 moles Al x 27.0 g Al = 81.0 g of Al1 mole Al

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Molar Mass is used as a conversion factor: 1 mole of CH4 = 16.0 g of CH4

16.0 g CH4 and 1 mole CH4

1 mole CH4 16.0 g CH4

Summary

Molar Massgrams moles particlesAvogadro’s

The mole is a scientific concept that allows for the counting of atoms by weighing them.

A mole is equal to the number of atoms in exactly 12 grams of pure C-12

12 g C = 1 mol C atoms = 6.02 x 1023 C atoms

Relating coefficients to moles

3 H2 + 1 N2 2 NH3

3 (molecules of H2 ) 1 (molecule of N2 ) 2 (molecules of NH3)

Impossible to work with such small quantities.

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Mole Relationships in Chemical Equations

:. Use a larger quantity, such as Avogadro's number 3(6.02 x 1023 molecules) 1(6.02 x 1023 molecules) 2(6.02 x 1023 molecules)

Since 6.02 x 1023 = 1 mole

3 moles 1 mole 2 moles

Therefore: coefficients = moles

The coefficients can be placed in the form of mole ratios, which serve as conversion factors.

the mole ratio of H2 to N2 is 3:1 3 mol H2

1 mol N2

the mole ratio of H2 to NH3 is 3:2 3 mol H2

2 mol NH3

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Example: How many moles of NH3 can be produced from 6.0 moles H2?

6.0 mole H2 x 2 mole NH3 = 4.0 moles NH3

3 mole H2

The “map” A pictorial view of the steps and conversion factors needed to find the answer.

moles

grams

MM

Mole Ratio

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Mass Calculations for Reactions

N2(g) + 3H2(g) 2NH3(g)

= 85.0 g NH3

Example: Suppose we want to determine the mass (g) of NH3 that can form from 2.50 moles N2.

N2(g) + 3H2(g) 2NH3(g)

moles

grams?

2.50

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2.50 mole N2

given

x 2 moles NH3

1 mole N2

mole ratio

x 17.0 g NH3

1 mole NH3

molar mass