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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