Writing and Balancing Chemical Equation

In writing chemical equation, you must have knowledge in writing chemical formulas.  Chemical formulas, symbols, arrow, + sign are part of chemical equation.  Chemical equation is a shortcut way of writing chemical reaction.  It gives you the reactants and the products.  Reactants are the substances that undergo reaction and the products are the result of the reaction.  Reactants are written in the left side of the equation and the products are written in the right side of the equation separated by an arrow.

  

Chemical equation also shows the phases of the reactants and products.

          s or arrow downward stands for solid

          l stands for liquid

          g or arrow upward stands for gas

          aq stands for salts or substance dissolved in water

But I want to emphasize how to write and balance chemical equation and so sample equations will not show the phases of the reactants and products.

HOW TO WRITE CHEMICAL EQUATION

When you write chemical equation make sure that it tells the truth, meaning correct symbols and formulas must be written.  You must be familiar with the different diatomic molecules, they are useful in writing chemical equations.

Example:  

1.  Carbon reacts with oxygen gas to form carbon dioxide.

Answer:

            

Carbon will be written in elemental form while oxygen as diatomic molecule. Carbon dioxide will have 1 atom of carbon and 2 atoms of oxygen.  It is understood that the oxidation of carbon used is 4 and oxygen is two.

2.  Sodium and oxygen react to form sodium oxide.

Answer:  

Sodium also will be in elemental form and oxygen will have a subscript of two since a diatomic molecule.  The formula of sodium oxide is, sodium having 2 subscript from the oxidation of oxygen and oxygen has subscript of 1 from the oxidation of sodium.  

As you can see the equation gives the correct formulas and symbols needed in the equation.  But if you will check the equation is not yet balanced.  Equation must be balanced to conform with the Law of Conservation of Mass.  According to the law the total mass of the reactants must be equal to the total mass of the products.  This can only be true if the equation is balanced.  

HOW TO BALANCE CHEMICAL EQUATION

In balancing chemical equation, you just need to follow several steps.  Below is the simplified way of balancing chemical equation.  

1.  First, write correctly the symbols and formulas of reactants and products.  And then count the number of atoms of the elements in the reactants side and in the products side. 

Example :  

1.  Write the balanced equation of the reaction between sodium  and oxygen  forming sodium oxide.

Reactant side                    Product side

Na  =  1                             Na  =  2

O    =  2                             O    =  1

Notice the number of atoms, sodium in the reactant side is only one but in the product side is 2 and oxygen in the reactant side is two while in the product side is only one.  This only indicates that the equation is not balanced.

2.  Balance the equation by writing coefficient written before the formula.  Coefficient must be a whole number and must be in a smallest ratio.   Subscript must not be change, if you do so, your changing the symbols and formulas of the elements and compounds in the equation.  This is a big NO NO in balancing equation.

From the above equation, we can balance it by writing coefficient 2 before sodium oxide to balance the oxygen and write 4 before the Na to balance the sodium atom.  

And to check if balance

       Na  =  4                                             Na  =   4

       O    =  2                                             O    =  2

Therefore the equation is already balanced.

Other examples:

1.  Write the balanced equation of the reaction between phosphorous and oxygen to form                           diphosphorous pentaoxide.

2.  Write the balanced equation between the reaction of Iron and chlorine to form Iron (III) chloride.

Solution:

1.  The equation looks like this:

     To balance, simply write 5 before oxygen and 2 before diphosphorous pentaoxide to balance the          oxygen, and to balance phosphorous write 4 before phosphorous.

2.  Equation in number 2 is:

     Balance by writing 3 before chlorine gas and 2 before Iron (III) chloride to balance the chlorine          and to balance Iron write 2 before Iron.

     That makes the Iron 6 and Iron 2, therefore the equation is balanced.