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What is a Chemical Equation?
A chemical equation is the form of representing the chemical reaction with the help of chemical formulas of the substances involved in the reaction. Reactants are the substances that react with each other in a chemical reaction and the products are substances that are obtained after reaction. The reactants are written in the left hand side of the chemical equation and the products are written on the right hand side. The two are separated by an 'arrow' (→). Here is a simple example of a chemical equation:
2H2 + O2 → 2H2O
In this chemical equation four molecules of hydrogen are combining with two molecules of oxygen (reactants) to give two molecules of water (product). If you were to count the number of atoms on either side of the equation, you would see that they are equal.
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Need for Balancing Chemical Equations
When a chemical reaction occurs, the reactants are converted to products. However, the number of atoms, remains the same before and after the reaction as per the law of conservation of mass. When you write a chemical equation, a necessary step is to balance the number of atoms on both sides of the equation.
For example, in the above reaction one molecule of hydrogen (H2) and an atomic form of oxygen (O) are sufficient to produce a molecule of water (H2O). But it is hard to find atomic oxygen. Hence, we represent it as molecule (O2).
H2 + O2 → H2O
As can be seen the amount of reactants is not equivalent to the products. Hence, it is an unbalanced equation, which has to be balanced to give the following balanced equation.
2H2 + O2 → 2 H2O
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Now, you know what a chemical equation is and why it should be balanced. Let us see how to balance these chemistry equations in a series of steps.
- Take the unbalanced equation and make a note of the elements present in each side of the equation.
- Now, count the number of molecules of each element present on both sides of the equation.
- Here comes the task of balancing the chemical equations. You should see that same numbers of molecules of all elements are present on the reactants side as well as the products side. The equation should follow law of conservation of mass i.e. matter is neither created nor destroyed.
- While balancing the equations you should only change the co-efficient of the chemical formula but not the subscripts. Changing the subscripts will change the components.
- Start by balancing one element at a time. Finally check if all the elements are balanced.
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One molecule of water is formed due to combination of two molecules of hydrogen with one molecule of oxygen.
H2 + O2 → H2O
However, this is an unbalanced reaction because there are two oxygen molecules on the reactants side but only one in the products side. Now proceed to balance this equation.
Step 1: Make a note of elements on the reactants side and products side.
Products [H] [O]
Step 2: Count the number of elements on each side.
Reactants: [2 Hydrogen atoms] [2 Oxygen atoms]
Products [2 Hydrogen atoms] [1 Oxygen atom ]
Step 3: Oxygen is unbalanced. Balance it so that there are two oxygen’s on both sides. Now the equation becomes.
H2 + O2 → 2 H2O
Step 4: Oxygen is balanced. Check if other elements are balanced. Hydrogen is unbalanced with two hydrogen atoms in reactants and four hydrogen atoms in the products. Now make it into four hydrogen atoms by multiplying the hydrogen molecule with two. Now the equation will be
2 H2 + O2 → 2H2O
So, there are four hydrogen atoms in both reactants and products and there are two oxygen atoms in both reactants and products. This means that the chemical equation is balanced.
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By using the above approach you can balance any chemistry equations. You can find some chemical equation balancing activities in the following links: