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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-