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Chapter 6: Chemical Reactions
Notes
What is a chemical reaction?
Examples:
Key Terms:
Reactant:
Product:
Example:
Word Equations
A word equation represents a chemical reaction.
All the _________________ are written on the ____________ of the yield arrow, separated by
a _________________ (if needed).
All the _________________ are written on the ________________ of the yield arrow,
separated by a ________ sign (if needed).
Reactant 1 + Reactant 2 -> Product 1 + Product 2
Try This:
Example: Rust
iron + oxygen -> iron (III) oxide
What are the reactants?
What are the products?
# 2. propane +oxygen -> carbon dioxide + water
a) List all the reactants in the reaction
b) List all the products in the reaction
c) What is the purpose of the arrow?
#3 Write word equations for the following reactions:
a) CaCl2 and Na2SO4 react to form CaSO4 and NaCl
b) BaCO3 reacts when heated to produce BaO and CO2
c) AgNO3 reacts with KCl to produce AgCl and KNO3
4. Write word equations to represent the following chemical reactions:
a)carbon dioxide and water are produced in a human cell during respiration. The reactants are
sugar and oxygen.
b) Stalactites form in caves when calcium bicarbonate reacts to form calcium carbonate, water
and carbon dioxide gas.
Can you figure out what is missing in the following chemical reactions?
1. Aluminum resists corrosion (rust) because it reacts with a gas in the air to form a protective
coating of aluminum oxide.
Aluminum + ____________-> aluminum oxide
2. Zinc Metal, used as a coating in galvanized iron, also reacts with air to form a coating that
resists further corrosion.
zinc+ oxygen->___________________
3. When aluminum foil is placed in a solution of copper (II) chloride, copper metal and another
solution are formed:
aluminum + copper (II) chloride ->
copper + ___________
4. When sodium sulfate and calcium chloride solutions are mixed, a precipitate of calcium
sulfate and another substance is formed.
sodium sulfate +calcium chloride ->
calcium sulfate +_________
Skeleton Equations:
 a representation of a chemical reaction in which the formulas of the reactants and products
are used instead of the names of the compounds.
Reactants are still separated from each other by a + and reactants and products are separated
by an arrow
Example: CH4 +O2 -> CO2 +H2O
Try these: Change the word equations into skeleton equations.
1. Iron reacts with Hydrogen sulfate to form Iron (III) Sulfate and Hydrogen Gas
2. Potassium hydroxide reacts with hydrogen phosphate to produce potassium phosphate and
hydrogen gas.
3. Ammonia and oxygen gas react to form Nitrogen monoxide and water.
Challenge:
4. Boron trifluoride and Lithium sulfite produce Diboron trisulfite and lithium fluoride.
But wait...
There's a problem with our skeleton equations....
Can you spot it?
Example: CH4 + O2 -> CO2 + H2O
Problem:______________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
The Law of Conservation of Mass
The law of conservation of mass states that:
-experiments show that atoms in a chemical reaction are not changed themselves, and the
number of atoms has to stay the same from before the reaction to after.
Refresher on Counting atoms:
How many atoms of each element are there in each molecule of:
a) H2SO4
b) Al2(SO4)3
c) CH3COOH
Try These:
1. When a log burns in your fire place, why are is the mass of the ashes less than the mass of
the log?
2. Count the number of atoms of each type of reactant in the reaction below and record them
in the table below. Count the number of atoms of each type of product and record them below.
b) What do your results say about conservation of mass.
Number of atoms Reactants Products
Carbon
Oxygen
Hydrogen
3. A solid has a mass of 35g. When it is mixed with a solution, a chemical reaction happens. If
the total mass of the products is 85g, what was the mass of the solution?
4. Solution A gas a mass of 60g. Solution B has a mass of 40g. When they are mixed, a
chemical reaction occurs in which a gas is produced. If the mass of the final mixture is 85g,
what mass of gas was produced?
Balancing Chemical Equations:
What's wrong with this reaction?
Al +Br2 -> AlBr3
______________________________________________
How do we fix that? __________________________________________________
Remember:
3 Na2SO4
Remember this rule above all else: YOU CANNOT CHANGE SUBSCRIPTS, only coefficients.
How to Balance:
Iron reacts with oxygen to form magnetic iron oxide (Fe3O4).
Step 1: ________________________________________________________________
Step 2: _______________________________________________________________
Step 3: ______________________________________________________________
Fe + O2-> Fe3O4
Reactants:
Products:
Fe: _____
Fe: _____
O:______
O:______
Step 4:
___________________________________
Try another:
Magnesium metal reacts with nitric acid (HNO3) to form hydrogen gas and magnesium nitrate.
Step 1: Write the word equation for the reaction
Step 2: Write the skeleton equation by replacing the formulas for the name.
Step 3: Count the number of atoms of each type in reactants and products.
****(in this case we can count the NO3- as one atom because it stays together)****
Mg+ HNO3 -> H2 + Mg(NO3)2
Reactants:
Mg:___
H: ____
NO3-: ________
Products:
Mg: ___
H: ___
NO3-: _____
You Try:
You try:
1. a) Why is the following equation not balanced?
N2 + H2 -> NH3
b) What is wrong with the way the above equation was balanced here?
N2 + H3 -> N2H3
2. Balance:
a) Na + Cl2 -> NaCl
b) K + O2 -> K2O
c) H2 + O2 -> H2O
d) H2 + Cl2 -> HCl
e) N2 + H2 -> NH3
f) CO + O2 -> CO2
g) Al + Br2 -> AlBr3
h) N2H4 + O2 -> H2O + N2
i) CH4 + O2 -> CO2 + H2O
3.For each of the following, write the correct skeleton equation, and then balance it to form a
chemical equation.
a) copper (II) oxide+hydrogen-> copper + water
b) lead (II) nitrate + potassium iodide ->lead (II) iodide + potassium nitrate
c) calcium+water ->calcium hydroxide+hydrogen
d) lead (II) sulfide +oxygen -> lead+sulfur dioxide
e) hydrogen sulfide -> hydrogen +sulfur