unit 12: classification of chemical reactions 1. chemical reactions a process that involves changes...
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UNIT 12: CLASSIFICATION OF CHEMICAL REACTIONS
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Chemical Reactions• a process that involves changes in the structure and energy content of atoms, molecules, or ions but not their nuclei.
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Most reactions occur in the aqueous phase (in water) because the particles can move about and interact with each other.
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Remember This?
• Dissolving- a solvent
surrounds a solute.
Watch This
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Formation of Solutions -Dissolving• A solute dissolving in a solvent requires energy.
• It can be an endothermic or exothermic process.
Is it a chemical reaction?
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Formation of Solutions- DissolvingCovalent molecules … • DO NOT break apart when dissolved.
•Ionic Compounds… • DO break apart when dissolved
• (this is considered a chemical change)
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Molarity• A unit of concentration The number of moles of solute
dissolved in 1.00 L of solution.
Molarity (M) = Moles of solute• Liter of solution
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Practice Problem• What is the molarity if 2.0 moles of glucose are added to
5.0 L of solution?
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Practice Problem
• Molarity (M) = Moles of solute Liter of solution
2.0 moles =.40 M
5.0 L
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How to prepare a solution
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Grams = Molarity X Liter X Molar Mass of Solutesolute
Watch This
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How to prepare a solution
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To make a concentrated solution more dilute use this formula M1V1 = M2V2
M1 = concentrated solutionV1 = amount of concentrated solution need to make dilute solutionM2= dilute solutionV2 – amount of diluted solution wanted.
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Law of Conservation of Matter• matter cannot be created or destroyed, it can only change forms.
• Therefore, in a chemical reaction the number of
atoms, the mass and the charge must be conserved.
Watch Thisreactants
products
Activated complex
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EQUATIONS
Balancing Equations –
In order to be balanced, the type and number of atoms must match on the reactant and product side
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Balancing Equations-Taking inventory
(l)22(g)2(g) OH2O H2 Reactants
• 4 hydrogen
•2 oxygen
Products
•4 hydrogen
•2 oxygen
In order to be balanced, the type and number of atoms must match on the reactant and product side
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Tutorial and Practice
• Tutorial• Watch This
• Practice
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• __H2S(g) + __SO2(g) __S(s) + __H2O(g)
Reactants Products
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__Fe2O3(s) + __H2(g) __Fe(s) + __H2O(g)
Reactants Products
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Types of Reactions• Combination/Synthesis/Composition A + B AB
• Decomposition AB A + B
• Single Replacement C+ AB AC + B
• Double Replacement AB + CD AD + CB
• Combustion CxHy + O2 CO2+ H2O
• Redox – any of the above where the oxidation number of two species changes
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Watch This
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Double ReplacementClue: Do-See-DohAB + CD AD + CB
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Combination 1• Also known as composition or synthesis; one product
http://genchem.chem.wisc.edu/demonstrations/Gen_Chem_Pages/04chemrxnpage/chemicalreactions.htm
___K (s) +___Br2 (l) ___KBr (s)
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Combination 2
____Zn (s) + ___I2 (l)____ ZnI2 (s)
http://genchem.chem.wisc.edu/demonstrations/Gen_Chem_Pages/04chemrxnpage/chemicalreactions.htm
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Decomposition
• Single reactant breaks down into two or more simpler substances
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Single Replacement• A single element replaces another element in a compound.• Must use activity series to determine if reaction will take place.
More active will replace less active.
___Cu (s)+ __AgNO3 (aq) __Cu(NO3 )2 (aq)+ ___Ag (s)
Remember:
Metal can only replace
metal (or hydrogen)
Nonmetal can only replace
nonmetal
SR animation
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Using the activity series: Watch This
.For a single replacement to occur, the solo metal must be more reactive than the metal it replaces.
The higher up on the list, the more reactive it is.
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Single Replacement• For a single replacement to occur, the solo nonmetal must be more reactive than the nonmetal it replaces.
• The higher up on the list, the more reactive it is.
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Double Replacement• Two reacting compounds, with metals trading places.
• A precipitate (insoluble solid) is formed.
___AgNO3 (aq)+ ____NaCl (s) ____NaNO3 (aq)+ ____AgCl (s)
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Determining solubility of products
• Use the solubility rules on the back of the periodic table.• The solubility rules are organized by the anion in the
compound.• Find the anion. * this is the negative ion *• Determine if, based on the cation, the compound is
soluble (aq) or insoluble (s) in water.• Write the (aq) or (s) after the compound• Practice:• AgCl
• K(NO3)
• PbS
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• Solubility Shortcuts – here’s all you need to remember:
• All group 1 metals
• All nitrates (NO3- )
• All acetates (C2H3O2- )
• All ammonium (NH4+ )
ARE ALWAYS SOLUBLE (aq)
Remember HAPStands for Mercury (Hg), Silver (Ag) and Lead (Pb)
Compounds with these elements are usually
INSOLUBLE (s)
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Try these:NaC2H3O2
Hg(OH)2
MgBr2
(NH4)2SO4
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Combustion
• _C3H8 + _O2 _ CO2 + _H2O + energy
• A combustion reaction is when oxygen combines with another compound to form water and carbon dioxide.
• It is highly exothermic
.
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OXIDATION-REDUCTION REACTIONS• a reaction where electrons are transferred between
reactants and products
• Watch This
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OXIDATION-REDUCTION REACTIONS a. Loss of Electrons is OXIDATION
i. oxidation number increases across the arrow.
b.Gain of Electrons is REDUCTION
i. oxidation number decreases across the arrow.
*LEO the Lion Says GER- These must occur together. Can’t have one without the other.
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OXIDATION-REDUCTION REACTIONS Oxidation Number (Oxidation State) – a method of
keeping track of electrons gained (reduced) and lost (oxidized).
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OXIDATION-REDUCTION REACTIONS
Rules for assigning oxidation numbersa. Atoms in their elemental form have an oxidation number of
zero. Cu = 0b. Monatomic ions have an oxidation number equal to their
charge. K+1= +1.c. Nonmetals have negative oxidation numbers.
i. Oxygen is -2 in all compounds with the exceptions of peroxides in which it is -1
ii. Hydrogen is usually +1 with nonmetals Hydrogen is usually -1 with metals
d. The sum of the oxidation number in an neutral compound is zero.
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OXIDATION-REDUCTION REACTIONSHow to identify a redox reaction.
a. Determine the oxidation number of each element in each compound.
b. Compare the reactants and products.
c.If there is a change in the oxidation number of any species, then it is redox.
d.Number increases across arrow = oxidation LEO
e.Number decreases across arrow = reduction GER
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OXIDATION-REDUCTION REACTIONSPractice- are the following redox reactions?
______ a. NaCl + AgNO3 --> NaNO3 +AgCl
______ b. FeCl2 + Cl2 FeCl3
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