2.1 Science and Technology in Society2.2 Changes in Matter2.3 Balancing Chemical Reactions2.4 Chemical Amount2.5 Classifying Chemical Reactions2.6 Chemical Reactions in Solution

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2.2 Changes in Matter

Chemical Reactions

Types of Changes in Matter

Physical Changes· Change in State· No new substance

Types of Changes in Matter

Nuclear Changes· Changes within the nucleus· Fusion and Fission (applets)

Types of Changes in Matter

Chemical Changes· A change in chemical bonds

· Hoffman Demo

Signs of a Chemical Change Production of heat and light Formation of a gas Formation of a precipitate Colour change

Why Do Reactions Occur? The kinetic molecular theory

states that matter is made up of tiny particles in continuous random motion.

The average kinetic energy (the energy of motion) of the particles depends on the temperature of the particles.

Solid           Liquid         

Gas                                                                                     

 

Types of Particle Motion

Translational motion: the motion of a particle in a straight line

Rotational movement: a spinning or turning of a molecule.

Motion Continued:

Vibrational movement: the back and forth motion within a molecule

These types of particle movement can be discussed with the three states of matter

KMT Continued:

The particles this theory refers to may be atoms (Na), ions (Na+) or molecules (CO2).

As the particles move, they collide with each other and objects in their path.

Collision Theory

Reaction rate depends on the collisions between reacting particles.

Successful collisions occur if the particles...· collide with each other· have the correct orientation · have enough kinetic energy to

break bonds

Collision Theory

Activation Energy (Ea)· minimum energy required for a

reaction to occur

ActivationEnergy

Collision Theory

Activation Energy· depends on reactants· low Ea = fast rxn rate

Ea

Factors Affecting Rxn Rate

Surface Area· high SA = fast rxn rate· more opportunities for collisions· Increase surface area by…

-using smaller particles-dissolving in water

Factors Affecting Rxn Rate

Concentration· high conc = fast rxn rate· more opportunities for collisions

Factors Affecting Rxn Rate

Temperature· high temp = fast rxn rate· high KE

- fast-moving particles-more likely to reach activation energy

Factors Affecting Rxn Rate

TemperatureAnalogy: 2-car collision

5 mph “fender bender”

50 mph “high-speed crash”

Factors Affecting Rxn Rate

Catalyst· substance that increases rxn rate

without being consumed in the rxn· lowers the activation energy· Burn a sugar cube with a catalyst

Exothermic Reaction

reaction thatreleases energy

products have lower energy than reactants

2H2(l) + O2(l) 2H2O(g) + energy

energyreleased

Endothermic Reaction

reaction that absorbs energy

reactants have lower energy than products

2Al2O3 + energy 4Al + 3O2

energyabsorbed

Law of Conservation of Mass mass is neither created nor destroyed

in a chemical reaction

4 H

2 O

4 H

2 O4 g 32 g

36 g

total mass stays the same atoms can only rearrange

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2.3 Balancing Chemical Reaction Equations

Chemical Reactions

Chemical Equations

Chemical reactions are represented by chemical equations

A chemical equation lists all of the compounds that participate in the reaction.

Chemical Equations

A+B C+DREACTANTS PRODUCTS

Chemical Equations

Writing Equations

Identify the substances involved. Use symbols to show:

2H2(g) + O2(g) 2H2O(g)

· How many? - coefficient· Of what? - chemical formula· In what state? - physical state

Writing Equations

Two atoms of aluminum react with three units of aqueous copper(II) chloride to produce three atoms of copper and two units of aqueous aluminum chloride.

• How many?• Of what?• In what state?

Al 2 (s) + 3CuCl2(aq) 3 Cu(s) + 2AlCl3(aq)

Describing Equations

to produce

• How many?• Of what?• In what state?

Zn(s) + 2HCl(aq) ZnCl2(aq) + H2(g)

One mole of solid zinc reacts withtwo moles of aqueous hydrochloric acid one moleof aqueous zinc chloride and onemole of hydrogen gas.

Balancing Steps

1. Write the unbalanced equation.

2. Count atoms on each side.

3. Add coefficients to make #s equal.

Coefficient subscript = # of atoms

4. Reduce coefficients to lowest possible ratio, if necessary.

5. Double check atom balance!!!

Helpful Tips

Balance one element at a time. Update ALL atom counts after adding

a coefficient. If an element appears more than

once per side, balance it last. Balance polyatomic ions as single

units.· “1 SO4” instead of “1 S” and “4 O”

Al + CuCl2 Cu + AlCl3

Al

Cu

Cl

1 1

1 1

2 3

2

3

6

3

33 2

Balancing ExampleAluminum and copper(II) chloride react to form copper and aluminum chloride.

2

2

6

The Mole

2.4 Chemical Amount

What is the Mole?A counting number (like a dozen)

Avogadro’s number (NA)

1 mol = 6.02 1023 items

A large amount!!!!

A mole of a compound is an observable quantity. It can be weighed and used in experiments.

LEFT: Proceeding clockwise from the top, samples containing one mole each of copper, aluminum, iron, sulfur, iodine, and (in the center) mercury.

1 mole of hockey pucks would equal the mass of the moon!

A. What is the Mole?

1 mole of pennies would cover the Earth 1/4 mile deep!

1 mole of basketballs would fill a bag the size of the earth!

One mole = 6.02 x 1023 atoms, molecules, or ions (Avogadro’s number)

When coefficients are used to balance chemical equations, they express a mole-to-mole ratio of the products and reactants.

These numbers do not represent the exact number of moles for the reactants or products, but rather give a ratio

we can use to compare quantities.

Molar MassMass of 1 mole of an element or

compound.

Atomic mass tells the... atomic mass units per atom (amu) grams per mole (g/mol)

Round to 2 decimal places

Molar Mass Examplescarbon

aluminum

zinc

12.01 g/mol

26.98 g/mol

65.39 g/mol

Molar Mass Exampleswater

sodium chloride

· H2O· 2(1.01) + 16.00 = 18.02 g/mol

· NaCl· 22.99 + 35.45 = 58.44 g/mol

Molar Mass Examplessodium bicarbonate

sucrose

· NaHCO3

· 22.99 + 1.01 + 12.01 + 3(16.00) = 84.01 g/mol

· C12H22O11

· 12(12.01) + 22(1.01) + 11(16.00) = 342.34 g/mol

Molar Conversionsmolar mass

(g/mol)

MASSIN

GRAMS

MOLESNUMBER

OFPARTICLES

6.02 1023

(particles/mol)

Molar Conversions

n = number of molesm = mass (g)M = Molar Mass (g/mol)

n = m/M

Molar Conversions

n = number of molesp = particlesNA = Avogadro's number

(6.02 x 1023 particles per mole)

p = n * NA

Molar Conversion ExamplesHow many moles of carbon are in 26 g of carbon?

26 g C 1 mol C12.01 g C

= 2.2 mol C

Molar Conversion ExamplesHow many molecules are in 2.50 moles of C12H22O11?

2.50 mol6.02 1023

molecules1 mol

= 1.51 1024

molecules C12H22O11

Molar Conversion ExamplesFind the mass of 2.1 1024 molecules of NaHCO3.

2.1 1024

molecules 1 mol6.02 1023

molecules

= 290 g NaHCO3

84.01 g1 mol

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Chemical Reactions

2.5 Classifying Chemical Reactions

Combustion

CH4(g) + 2O2(g) CO2(g) + 2H2O(g)

the burning of any substance in O2 to produce heat

A + O2 B

Na(s)+ O2(g)

C3H8(g)+ O2(g) 5 3 4

Combustion

Products:· contain oxygen· hydrocarbons form CO2 + H2O

CO2(g)+ H2O(g)

Na2O(s) 4 2

Synthesis/Formation

the combination of 2 or more substances to form a compound

only one product

A + B AB

Synthesis

H2(g) + Cl2(g) 2 HCl(g)

Al(s)+ Cl2(g) AlCl3(s)2 3 2

Synthesis

Products:· ionic - cancel charges· covalent - hard to tell

Decomposition

a compound breaks down into 2 or more simpler substances

only one reactant

AB A + B

Decomposition

2 H2O(l) 2 H2(g) + O2(g)

KBr(l) K(s) + Br2(l) 2 2

Decomposition

Products:· Binary ionic - break into elements· others - hard to tell

Single Replacement

one element replaces another in a compound· metal replaces metal (+)· nonmetal replaces nonmetal (-)

A + BC B + AC

Single Replacement

Cu(s) + 2AgNO3(aq) Cu(NO3)2(aq) + 2Ag(s)

AB + CD AD + CB

Double Replacement

ions in two compounds “change partners”

cation of one compound combines with anion of the other

Double Replacement

Pb(NO3)2(aq) + K2CrO4(aq) PbCrO4(s) + 2KNO3(aq)

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

Double Replacement

Products:· switch negative ions· one product must be insoluble

(check solubility table)

NaNO3(aq)+ KI(aq) N.R.

2 2

Chemical Reactions in

SolutionSection 2.6

Why in Solution? Often reactions are carried out in

solution in order to speed up the rate of reaction.

Dissolving something makes the particles smaller (increase surface area)

We can add heat or stir May be a way to dilute volatile

substances to make the reaction safer.

Solubility Refers to an ionic compound’s ability to

dissolve in water If a compound is soluble (completely

dissolves in water) it is considered to be aqueous.

Aqueous solutions are labeled with the letters (aq) after the chemical formula

Example: NaCl(aq)

If an ionic compound is not soluble in water, it will remain as a solid (it will form a precipitate).

Solids are labeled with a (s) after the compound formula.

Example: Ag2SO4(s)

How to use the Solubility Table

The solubility table will tell us if an ionic compound is soluble in water.

Steps to follow:1) Determine the non-metal of

your compound and find it on the top of the chart.

2) Look beneath the non-metal on the chart. If the metal it is matched with is in the section labeled “high solubility”, the compound is soluble in water.

- the compound is then labeled with a (aq)

3) If the metal is located in the section labeled “low solubility”, your compound is not soluble in water.-the compound is then labeled

with a (s)

SEE PAGE 8 IN YOUR DATA BOOKLET

Examples: Are these ionic compounds soluble in

water?

Ag+ and SO42- Ca2+ and S2-

K+ and NO3- Li+ and OH-