Download Writing Chemical Equations KClO3 O2 (g) + KCl (s) Balancing

Chemistry
with Mr. Torre
Writing Chemical Equations
A + B
Reactants
Ingredients (Before) A chemical equation will look something like this:
AB
Products
Cake (After)
The following symbols are used in equation to describe substances and how they react.
Used to separate two reactants or two products
+
“Yields,” separates reactants from products
(s)
(l)
(g)
(aq)
,
Used in place of a
for reversible reactions.
Indicates a solid reactant or product.
Indicates a liquid reactant or product.
Indicates a gaseous reactant or product.
Indicates an aqueous reactant or product; a substance dissolved in water.
Indicates a gaseous product; alternative to (g)
Indicates a solid product; alternative to (s)
Triangle or “heat” above or below the yield symbol indicates that heat is supplied to the
reaction.
A formula written above or below the yield symbol indicates that a catalyst is used. In this
example Platinum is the catalyst.
Example: NaHCO3 (s) + HCl (aq) NaCl (aq) + H2O (l) + CO2 Would read: Solid sodium hydrogen carbonate reacts with aqueous hydrochloric acid to produce aqueous sodium
chloride, liquid water and gaseous carbon dioxide.
Example2: Oxygen gas can be made by heating potassium chlorate in the presence of the catalyst manganese(IV)
oxide. Potassium chloride is left as a solid residue.
The equation would look like:
KClO3
O2 (g) + KCl (s)
Note: Oxygen is a diatomic element so it exists as O2 in its pure form. Other diatomic elements are
iodine (I2), bromine (Br2), chlorine (Cl2), fluorine (F2), nitrogen (N2), and hydrogen (H2).
Balancing Equations
Consider the Law of Conservation of Matter: “Matter can be neither created nor destroyed.”
The same number of atoms of each element must exist on the reactant side (“before” side) as on the product side (“after”
side).
H 2O H 2 + O 2
[unbalanced equation]
In this example we started with 2 atoms of hydrogen and we ended with 2 atoms of hydrogen. But we started with only
one atom of oxygen and ended with 2 atoms of oxygen. We cannot change the numbers at the bottom of the symbols
because that is how the formulas must be written. To balance the equation we put numbers in front of the formulas to
multiply the number of atoms in each formula.
2H2O 2H2 + O2
This gives us 4 atoms (2x2) of hydrogen before and 4 atoms of hydrogen after; 2 atoms (2x1) of oxygen before and 2
atoms of oxygen after.
Example 2 is more difficult:
Al + O2 Al2O3 (unbalanced)
Try listing the elements beneath the yield symbol and keep track of the numbers of atoms of each element there.
Al + O2 Al2O3
1 Al 2
2 O 3
4Al + 3O2 2Al2O3 (balanced)
4 Al 4
6 O 6