Download - Chapter 8
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Chapter 8
Describing Chemical Reactions
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Making Chili
1 lb browned hamburger16 oz can tomato sauce2 – 16 oz cans of red kidney beans1 lb chopped onion3 chopped green peppers3 cloves fresh garlic½ cup chili powder2 tbsp olive oil
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Chemical Reactions
A chemical reaction is the process by which one or more substances change into one or more new substances.
Reactants are the original substances in a chemical reaction.
Products are the substances that are created in a chemical reaction.
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Chemical Reactions
How to make chili
Ingredients + heat chili
How to make water
2 H2 + O2 2 H20
Reactants Products
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Evidence of a chemical change
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Evidence of a chemical change
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Evidence of a chemical change
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Chemical v. Physical
chemical change – new substance forms with properties that differ from original substance– density– boiling point– melting point
physical change - changes of state – evaporation– condensation– melting– freezing
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Constructing a Chemical Rxn
A chemical equation shows the chemical formulas and relative amounts of all reactants and products.
A word equation contains the names of the reactants and products.
Equations must be balanced.
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Constructing a Chemical Rxn
Word Equation
methane + oxygen carbon dioxide + water
Formula Equation
CH4 + O2 CO2 + H2O
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Constructing a Chemical RxnOther symbols
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Chapter 8
The Great Balancing Act
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Think…
Law of Conservation of Mass states that mass cannot be created or destroyed by a chemical or physical change
Therefore, ALL chemical equations must be balanced. That is, having the same number of atoms on both sides of the arrow
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Balancing Equations
The number of atoms for each element must be the same on the reactants’ side and on the products’ side.
A coefficient multiplies the number of atoms of each element in the formula that follows.
H2O: 2 hydrogen atoms, 1 oxygen atom
2H2O: 4 hydrogen atoms, 2 oxygen atoms
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Sample Problem
• Balance the equation for the reaction of iron (III) oxide with hydrogen to form iron and water.
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Sample Problem
• Aluminum reacts with arsenic acid, HAsO3, to form H2 and aluminum arsenate. Write a balanced equation for this reaction.
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Summarize the steps
1. NEVER CHANGE CHEMICAL FORMULAS!
2. Draw a table that shows the number of atoms before and after the arrow
3. Change the equation so that the number of each element are the same before and after the equation. Do this by adding COEFFICIENTS
4. Redo the table to match change, and repeat as needed.
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Chapter 8
Reaction Types
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The 5 Reaction Types
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Synthesis Reactions
In a synthesis reaction a single compound forms from two or more reactants.
Two elements form a binary compound
C + O2 CO2
2C + O2 2CO
Two compounds form a ternary compoundCaO(s) + H2O(l) Ca(OH)2(s)
CO2(g) + H2O(l) H2CO3(aq)
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Decomposition Reactions
In a decomposition reaction a single compound breaks down, often with the input of energy, into two or more elements or simpler compounds.
Decomposition of waterelectricity
heatCaCO3(s) CaO(s) + CO2(g)
A metal carbonate decomposes to form a metal oxide and carbon dioxide.
2H2O(l) O2(g) + 2H2(g)
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Sample Problem
Predict the product(s) and write a balanced equation for the reaction of potassium with chlorine.
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Double-Displacement Reactions
• In a double-displacement reaction two compounds in aqueous solution appear to exchange ions and form two new compounds.
• One of the products must be a solid precipitate, a gas, or a molecular compound, such as water.
HCl(aq) + NaOH(aq) HOH(l) + NaCl(aq)
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Displacement Reactions
In a displacement reaction a single element reacts with a compound and displaces another element from the
compound.
2Al(s) + 3CuCl2(aq) 2AlCl3(aq) + 3Cu(s)
Aluminum displaces copper.
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Sample Problem
• Determining Products by Using the Activity Series Magnesium is added to a solution of lead(II) nitrate. Will a reaction happen? If so, write the equation and balance it.
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Combustion Reactions
A combustion reaction is a reaction of a carbon based compound with oxygen.
Combustion of propaneC3H8 + 5O2 3CO2 + 4H2O
Combustion of ethanolCH3CH2OH + 3O2 2CO2 + 3H2O
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