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Physical science
2016
Review: the 5 signs of a chemical
reaction
1.
Production of an odor
 Examples: egg rotting, cooking
2. Change in temperature
 Some reactions release energy (exothermic)

Exo – means out or to leave
 Some reactions absorb energy (endothermic)

Endo – means into or to come in
3. Change in color
4. Formation of gas (bubbles)
5. Formation of a solid (precipitate)
What is a precipitate?
 Soluble: able to dissolve in water
 Example: salt and sugar
 Insoluble: unable to dissolve in water
 https://www.youtube.com/watch?v=w5ZHrV60dto
 A precipitate is a solid, insoluble compound in
solution.
 http://phet.colorado.edu/en/simulation/soluble-salts
Chemical Reactions Review
 Reactants: on the left of the arrow
 The stuff you start with
 Products: on the right of the arrow
 The stuff you make (new composition/formula)
 Law of Conservation of Mass: Matter cannot be
created nor destroyed during a chemical reaction
Types of Reactions
 There are 5 types of reactions:
1. Synthesis (bringing things together)
2. Decomposition (breaking something apart)
3. Single replacement (element and compound react)
4. Double replacement (two ionic compounds react)
5. Combustion (you guessed it…burning…of a
hydrocarbon)
What’s a hydrocarbon?
 Organic compound containing hydrogen, carbon, and
sometimes oxygen.
#1) Synthesis Reaction
#2) Decomposition reaction
Single replacement reaction
#4)Double Replacement
Reaction
#5) Combustion reaction:
Always add oxygen gas to hydrocarbon
Always makes water and carbon dioxide
hydrocarbon
Something New: Coefficients
 You know that matter cannot be created nor
destroyed in a chemical reaction.
 But did you know that when we write chemical
reactions, we must balance the atoms on both sides of
that arrow?
 EXAMPLE:
 H2 + O2 H2O
 Is this reaction balanced? You have 2 oxygen atoms
and 2 hydrogen atoms on the reactant side. You have 2
hydrogen atoms and only ONE oxygen atoms in the
products! WHAT TO DO????!!!!!
Balancing reactions
 In order to balance chemical reactions, we can use
large numbers placed in the front of any chemical
formula in a chemical reaction. Coefficients will
multiply the overall number of atoms in the chemical
formula.
 Example:
2H O
= 2 (2 hydrogen atoms and 1 oxygen
atom) =
 4 hydrogen atoms and 2 oxygen atoms.
 This gives us TWO water molecules:
2
Balance it!
 O2 + H2  H2O
 So how would you balance that equation?
 ____ H2 + ___ O2 +  ____ H2O
Coefficients are tricky:
How many of each atom?
2 Mg(NO3)2
3 K2SO4
4 Ca(C2H3O2)2
2 Mg, 4 N, 12 O
6 K, 3 S, 12 O
4 Ca, 16C, 24 H, 16 O
Balancing takes practice…use an
atom inventory!
 ___ Al + ___ Br2  ___ AlBr3
Al: 1
Br: 2
Al: 1
Br: 3
 Aluminum is balanced but bromine is not. 2 on the
left, 3 on the right. What’s the common multiple?
Keep going.
 ___ Al + ___ Br2  ___ AlBr3
Al: 1
Br: 6
Al: 2
Br: 6
 Now Bromine is balanced. But what happened to
Aluminum? Can you balance it?
Finally
 ___ Al + ___ Br2  ___ AlBr3
Al: 2
Br: 6
Al: 2
Br: 6
 Everything checks out. YAY!
Solubility rules
 On the back of the periodic table is another list: the
solubility rules.
 Not all ionic compounds placed in water will dissolve.
Some substances have such a strong ionic bond that
not even water can break them up.
 Give it a try: find these on the list and determine if
they are able to dissolve in water:
1. Ca(NO3)2
2. Ca(OH)2
3. Na2CO3
4. FeCO3
Examples:
Ca(NO3)2 = calcium nitrate. All nitrates are soluble.
No exceptions. This is soluble = aq
2. Ca(OH)2 = calcium hydroxide. All hydroxides are
insoluble EXCEPT those of alkali metals and Ca, Sr,
and Ba. This is soluble = aq
3. Na2CO3 = sodium carbonate. All carbonate, sulfites,
phosphates, and chromates are insoluble except
those of alkali metals and ammonium. Sodium is an
alkali metal. This is soluble = aq
4. FeCO3 = iron (II) carbonate. Same rule as above, but
iron is NOT an alkali metal. This is insoluble = s
1.