Balancing Equations

What is a chemical equation? 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. ( YIELD)

Types of reactions SYNTHESIS – 2 or more substances react to form a single product X + Y  Z DECOMPOSITION- a single reactant breaks down into 2 or more products. A  B + C

Types of reactions SINGLE REPLACEMENT – one element replaces another in a compound such that an element combines with a compound to produce and element and a compound. X +YZ  XZ + Y DOUBLE REPLACEMENT – 2 compounds react to make 2 different compounds AB + CD  AD +CB

Types of reactions COMBUSTION- one reactant (a fuel) combines with oxygen to produce an oxide and water (H 2 O) Fuel + O 2  CO 2 + H 2 O

Aluminum + Oxygen --> Aluminum Oxide Al + O 2  Al 2 O 3 You can see by looking at it that there is something wrong with this equation. Al = 1Al = 2 O = 2O = 3  If you count the number of atoms of each type on each side, you will see that there is only one aluminum atom on the left side whereas there are two on the right.  There are two oxygen atoms on the left side, as compared to three on the right side.  This clearly doesn't match.

Al + O 2  Al 2 O 3 Remember the lowered numbers are subscripts. You can’t change those. The number in front is called a Coefficient. It multiplies everything behind it by that number. This is what you change to make the number of elements equal on both sides of arrow

Al + O 2  Al 2 O 3 Pick an element that is not balanced. Oxygen for example. Al + O 2  Al 2 O 3 Count how many on each side: 2O  3O Multiply either or both sides to make them equal Al + 3O 2  2Al 2 O 3 3 x 2 = 62 x 3 = 6 6 O You put the coefficients in the front of the complete formulas. This will change the number of the other elements in the formula also.

Al + 3O 2  2Al 2 O 3 Now do aluminum Count the Aluminums on each side: 1 aluminum  4 Al 4 x 1  4 Al 4Al + 3O 2  2Al 2 O 3 4Al 4 Al6O Balanced

Law of Conservation of matter In a chemical reaction, Atoms can not be created nor destroyed. The atoms are only rearranged. All the atoms that are present in the reactants must also be present in the products. This means there must be the same number of each type of atoms on the reactants side and the products side of a chemical reaction.