chapter 4 chemical reactions
DESCRIPTION
Chemistry B11. Chapter 4 Chemical Reactions. Chemical Reactions. Chemical change = Chemical reaction. Substance(s) is used up (disappear). New substance(s) is formed. Different physical and chemical properties. Chemical Reactions. Chemical Reactions. A + B C + D. Reactants. Products. - PowerPoint PPT PresentationTRANSCRIPT
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Chapter 4
Chemical Reactions
Chemistry B11
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Chemical Reactions
Chemical change = Chemical reaction
Substance(s) is used up (disappear)
New substance(s) is formed.
Different physical and chemical properties.
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Chemical Reactions
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A + B C + D
Reactants Products
Chemical Reactions
Chemical Equation
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Chemical Reactions
A + B AB1. Synthesis reaction (combination)
2H2 + O2 2H2O
AB A + B2. Decomposition (analysis)
2NaCl 2Na + Cl2
A + BC AC + B3. Single replacement reaction
Fe + CuSO4 FeSO4 + Cu
AB + CD AD + CB4. Double replacement reaction
NaCl + AgNO3 NaNO3 + AgCl
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5. Combustion
C3H8 + 5O2 3CO2 + 4H2O
Chemical Reactions
Solid (s)Liquid (l)Gas (g)
Aqueous (aq)
Ca(OH)2(s) + 2HCl(g) CaCl2(s) + H2O(l)
AB + xO2 yCO2 + zH2O
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Why balancing?
Balance a chemical equation
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Balance a chemical equation
Law of conservation of mass
Atoms are neither destroyed nor created.
They shift from one substance to another.
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Balance a chemical equation
1. Begin with atoms that appear in only one compound on the left and right.
2. If an atom occurs as a free element, balance it last.
3. Change only coefficients (not formulas).
C3H8(g) + O2(g) CO2(g) + H2O(g)
last
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Formula and Molecule
Ionic & covalent compounds Formula formula of NaCl
Covalent compounds Molecule molecule of H2O
Formula Weight of NaCl:
23 amu Na + 35.5 amu Cl = 58.5 amu NaCl
Molecular Weight of H2O:
2 (1 amu H) + 16 amu O = 18 amu H2O
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Mole
Mole (mol): formula weight of a substance (in gram).
12g of C = 1 mol C 23g of Na = 1 mol Na
58.5 g of NaCl = 1 mol NaCl
18 g of H2O = 1 mol of H2O
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Avogadro’s number (6.02×1023): number of formula units in one mole.
1 mole of apples = 6.02×1023 apples
1 mole of A atoms = 6.02×1023 atoms of A
1 mole of A molecules = 6.02×1023 molecules of A
1 mole of A ions = 6.02×1023 ions of A
Molar mass (g/mol): mass of 1 mole of substance (in gram)(Formula weight)
molar mass of Na = 23 g/molmolar mass of H2O = 18 g/mol
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Relationships between amounts of substances in a chemical reaction.
Look at the Coefficients!
Stoichiometry
2H2O(l) 2H2(g) + O2(g)
2 moles 2 moles 1 mole
2 2 1
2 liters 2 liters 1 liter
2 particles 2 particles 1 particle
2 grams 2 grams 1 gram
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Amole
Bmolemass
volume volume
Particle(atom)
(molecule)(ion)
Particle(atom)
(molecule)(ion)
mass
CH4 + 2O2 CO2 + 2H2O
1 step: use coefficient in the balanced equation.
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CH4 + 2O2 CO2 + 2H2O
10 cc O2 = ? cc CO2 10 cc O2 (1 cc CO2
2 cc O2
) = 5 cc CO2
23 mole CH4 = ? moles H2O 23 mole CH4 (2 moles H2O
1 mole CH4
) = 46 moles H2O
40 g CH4 = ? L CH4 40 g CH4 (1 mole CH4
16 g CH4
) = 56 L CH4
22.4 L CH4
1 mole CH4
)(
STP: 1 mole of substance (gas) = 22.4 L = 22400 cc (cm3 or mL)
32 g CH4 = ? moles CO2 32 g CH4 (1 mole CH4
16 g CH4
) = 2 mole CO2
1 mole CO2
1 mole CH4
)(
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Limiting Reagents
N2(g) + O2(g) 2NO(g)
1 mole 1 mole 2 moles
1 mole 4 moles
0 mole 3 moles 2 moles
Before reaction:
After reaction:
Stoichiometry:
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Limiting Reagents
N2(g) + O2(g) 2NO(g)
1 mole 1 mole 2 moles
1 mole 4 moles
0 mole 3 moles 2 moles
Before reaction:
After reaction:
Stoichiometry:
Used up first Left over
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Limiting Reagents
N2(g) + O2(g) 2NO(g)
1 mole 1 mole 2 moles
1 mole 4 moles
Limiting reagent
0 mole 3 moles 2 moles
Before reaction:
After reaction:
Stoichiometry:
Used up first Left over
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Limiting Reagents
Limiting reagents can control a reaction:
N2(g) + O2(g) 2NO(g)
Limiting reagent: is the reactant that is used up first.
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Limiting Reagents
Example:
C(s) + O2(g) CO2(g) 12g of C64g of O2
? Limiting reagent? g of CO2 will be formed
Make sure that the chemical equation is balanced.
12g C (1 mole C
12g C) = 1 mole C
64g O2 (1 mole O2
32g O2
) = 2 mole O2
C is the limiting reagent.
C(s) + O2(g) CO2(g)
1 mol 1 mol 1 mol
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Limiting Reagents
We should use the mass of the limiting reagent.(because it controls our reaction).
12g C (1 mole C
12g C)(
1 mole CO2
1 mole C)(
44g CO2
1 mole CO2
) = 44g CO2
? g of CO2 will be formed: C(s) + O2(g) CO2(g)A B
12g 64g ? g
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Percent Yield
Percent yield = actual yield
theoretical yield× 100
actual yield: mass of product formed (experimental)
theoretical yield: mass of product that should form (according to stoichiometry)
N2(g) + O2(g) 2NO(g)
theoretical yield = 40g NOactual yield = 37g NO Percent yield =
37g NO
40g NO× 100 = 92.5%
7.5% error or lost
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Aqueous Solution (ionic compounds)
NaCl(s) Na+(aq) + Cl-(aq) Dissociation (Ionization)
aqueous solution: solvent is water
H2O
AgNO3(s) Ag+(aq) + NO3-(aq)
H2O
NaCl AgNO3
NaCl(aq) + AgNO3(aq) AgCl(s) + NaNO3(aq)
H2O
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Molecular equation:
2As3+(aq) + 3s2-(aq) As2S3(s)
total charge on left side = total charge on right side
NaCl(aq) + AgNO3(aq) AgCl(s) + NaNO3(aq)
Na+(aq) + Ag+(aq) + Cl-(aq) + NO3-(aq) AgCl(s) + Na+(aq) + NO3
-(aq)Ionic equation:
Net ionic equation:
Na+(aq) + Ag+(aq) + Cl-(aq) + NO3-(aq) AgCl(s) + Na+(aq) + NO3
-(aq)
Spectator ions
Ag+(aq) + Cl-(aq) AgCl(s)
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Oxidation and Reduction reactions (redox)
Zn(s) Zn2+(aq) + 2e- Zn is oxidized (reducing agent)
Cu2+(aq) + 2e- Cu(s) Cu2+ is reduced (oxidizing agent)
oxidation: is the loss of electrons.
reduction: is the gain of electrons.
Zn(s) + Cu2+(aq) Zn2+(aq) + Cu(s) redox reaction
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Oxidation and Reduction reactions (redox)
oxidation: is the gain of oxygen / loss of hydrogen.
reduction: is the loss of oxygen / gain of hydrogen.
CH4(s) + 2O2(g) CO2(g) + 2H2O(g) redox reaction
C gains O and loses His oxidized
(reducing agent)
O gains HIs reduced
(oxidizing agent)
single replacement reactions and combustion reactions redox reactions
double replacement reactions non redox
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Heat of reaction
C3H8(s) + 5O2(g) 3CO2 + 4H2O + heat (energy)
2HgO(s) + heat (energy) 2Hg(l) + O2(g)
Endothermic reaction
Exothermic reaction
All combustion reactions are exothermic.