What is a chemical equation?
Name
_______________
When a chemical reaction occurs, it can be described by an equation. This shows
the chemicals that react (called the reactants) on the left-hand side, and the
chemicals that they produce (called the products) on the right-hand side. The
chemicals can be represented by their names or by their chemical symbols.
Unlike mathematical equations, the two sides are separated by an arrow, that
indicates that the reactants form the products and not the other way round.
Take a look at this chemical word equation:
Aluminium + Oxygen
Aluminium Oxide
This is the equation for the burning of aluminium in oxygen. If we convert each of
the chemical names into the appropriate symbols, we get the following:
2Al + O2
Al2O3
Practice
Count the atoms and tell whether the chemical equation is balanced. Place a circle
around the reactants and a rectangle around the products.
1. Zn + 2HCl ---> ZnCl2 + H2
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2. S8 + F2 ---> SF6
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3. 2C2H6 + 7O2 ---> 4CO2 + 6H2O
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4. C3H8 + 5O2 ---> 4H2O + 3CO2
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5. C5H12 + 8O2 ---> 5CO2 + 6H2O
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Counting Atoms
Name _____________________
The formula for a compound indicates the elements that make up the compound and
the number of atoms of each element present in the compound. These numbers of
atoms are indicated by the use of small numbers called subscripts. When a
subscript appears outside the parentheses, it indicates that all the elements inside
the parentheses should be multiplied by that subscript. For example, the formula
Fe(OH)3 indicates the combination of one atom of iron, Fe. three atoms of oxygen,
O, and three atoms of hydrogen, H.
In the following examples, list each element in the compound and the number of
atoms of each element present. The first example has been done for you. You may
already be familiar with some of the compounds.
Name
Use
Formula
Calcium carbonate
limestone
CaCO3
Aspirin
pain reliever
C9H8O4
Acetic Acid
found in vinegar
C2H402
Pyrite
Fool’s Gold
FeS2
Trinitrotoluene
(TNT)
explosive
C7H5(NO2)3
Paradichlorobenzene
moth balls
C6H4Cl2
Atoms in Formula
Ca = calcium – 1
C = carbon – 1
O = oxygen - 3