chapter 8: describing chemical reactions chemical...
TRANSCRIPT
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Chapter 8.1
Chapter 8:
Describing Chemical Reactions
Chemical Equation – uses symbols and formulas to represent the identity and
relative amounts of reactants and products in a chemical reaction.
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Chapter 8.1
Indications of a Chemical Reaction
Evolution of heat and light
Production of a gas
Formation of a precipitate
Color change
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Word equation – an equation in which the reactants and
products in a chemical reaction are represented by
words.
hydrogen + oxygen water
Magnesium + oxygen
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Chapter 8.1
formula equation – represents the reactants and products in a chemical reaction by
their symbols or formulas.
H2 + O2 H2O
A formula equation is not necessarily balanced.
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Chapter 8.1
For an equation to be balanced, the same number of each type of atom must be
represented on both sides of the equation.
2 H2 + O2 2 H2O
H=2x2=4 H=2x2=4
O=2x1=2 O=2x1=2
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Balance the following chemical Equation:
HCl + Mg MgCl2 + H2
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Balancing Chemical Equations
1. Identify the names of reactants and products and write the word equation.
2. Write a formula equation for the reaction by substituting the correct formulas for the reactants and products.
Chapter 8.2
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3. Balance the formula equation according to the Law of Conservation of Mass.
4. Count Atoms to be sure that the equation is balanced.
Chapter 8.2
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Guidelines for Balancing Equations
Balance the different types of atoms one at a time.
First balance the atoms of elements that are combined and that appear only once on each side of the equation.
Chapter 8.2
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Balance polyatomic ions that appear on both sides of the equation as single units.
Balance hydrogen and oxygen atoms after atoms of all other elements have been balanced.
Chapter 8.2
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Common Mistakes
Writing incorrect formulas for reactants or products.
Trying to balance the equation by changing the subscripts.
Chapter 8.2
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Types of Chemical Reactions:
There are trillions of possible combinations for mixing reactants together to get products.
However, each of those trillions of possible combinations fall into 5 categories or types of chemical reactions:
1. Synthesis
2. Decomposition
3. Single Replacement
4. Double Replacement
5. Combustion
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Types of Chemical Reactions
Synthesis Reactions
Also known as a composition reaction
Two or more substances combine to form a new compound.
A + X AX
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Types of Reactions Examples:
The combination of an element with oxygen to produce the oxide of the element.
Magnesium + oxygen Magnesium Oxide
Calcium + oxygen Calcium Oxide
Potassium + oxygen
Most metals react with the halogens to form either ionic or covalent compounds.
Berylium + Chlorine Berylium Chloride
Aluminum + Bromine Aluminum Bromide
Strontium + Fluorine
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Decomposition Reactions
A single compound undergoes a reaction that produces two or more simpler
compounds.
AX A + X
A and X can be elements or compounds.
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Types of Reactions Examples:
Decomposition of Binary Compounds.
Simplest kind of decomposition reaction2 H2O 2H2 + O2
Electrolysis – The decomposition of a substance by electric current
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Types of Reactions
Decomposition of Metal Carbonates
CaCO3 CaO + CO2
Decomposition of Metal Hydroxides
Ca(OH)2 CaO + H2O
** Water and Carbon Dioxide are very stable, form them when you can!!!**
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Decomposition of Metal Chlorates
2KClO3 2KCl + 3O2
Decomposition of Acids
H2CO3 (aq) CO2 (g) + H2O (l)
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Single Replacement Reactions
One element replaces a similar element in a compound. (aka displacement)
A + BX AX+ B
Y + BX BY+ X
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Replacement of a metal in a compound by another metal
2Al(s) +3Pb(NO3)2(aq) 3Pb(s) + 2Al(NO3)3(aq)
Types of Reactions Continued
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Replacement of hydrogen in water by a metal
Active metals:
2Na (s) + 2H2O(l) 2NaOH(aq) + H2(g)
Less active metals:
3Fe(s) + 4H2O(g) Fe3O4(s) + 4H2(g)
Types of Reactions Continued
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Replacement of Halogens
Br2(g) + 2KI(aq) 2KBr(aq) + I2(l)
Types of Reactions Continued
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Double Replacement Reactions
The ions of two compounds exchange places in aqueous solution to form two
new compounds.
AX + BY AY + BX
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Formation of a precipitate
2KI(aq) + Pb(NO3)2(aq)PbI2(s) + 2KNO3(aq)
Formation of a gas
FeS(s) + 2HCl(aq) H2S (g) + FeCl2(aq)
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Formation of water Acid and Base Reaction
HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)
Types of Reactions Continued
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Combustion Reactions
A substance combines with oxygen, releasing a large amount of energy in the
form of heat and light
2C2H6(g) + 7 O2(g) 4CO2(g) +6H2O(g)
Types of Reactions Continued