Table of contents |
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Chemical Equation and Rule for Writing Chemical Equations |
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Enhancing Chemical Equations |
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Rules for Writing a Word Equation |
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Steps to Balance Chemical Equations |
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Solved Examples |
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Balancing a chemical equation involves adjusting the number of molecules or atoms of each substance so that the number of atoms of each element is equal on both sides of the equation.
This isn’t just a rule—it's a reflection of two fundamental scientific laws: the Law of Conservation of Mass (matter can’t be created or destroyed) and the Law of Constant Proportions (elements combine in fixed ratios). By adding the correct numbers, or coefficients, we ensure that the equation tells the true story of what’s happening in the reaction.
A chemical equation is a symbolic representation of a chemical reaction in which the reactants and products are denoted by their respective chemical formulae.
Example of a Chemical Equation
2H2 + O2 → 2H2O
This equation describes the reaction between hydrogen and oxygen to form water.
Key Components of Chemical Equation
To make a chemical equation more informative, include:
1. Physical States: Indicate the state of each substance using standard symbols:
(g): Gaseous state
(l): Liquid state
(s): Solid state
(aq): Aqueous solution
2. Reaction Conditions: Specify conditions like temperature, pressure, or catalysts, typically written above or below the arrow.
Example: N2 + 3H2 2NH3 + 22400 calorie heat
3. Special Symbols:
(↑): Indicates a gas evolved (e.g., H₂ (↑)).
Example: 2Na(s) + 2H2O(l) → 2 NaOH(aq) + H2(g) or H2 (↑). This shows sodium reacting with water to produce sodium hydroxide and hydrogen gas.
(↓) : Indicates a precipitate formed (e.g., AgCl (↓)).
Example: NaCl + AgNO3 → NaNO3 + AgCl (↓)
(→): Represents an irreversible reaction.
Example: 2H2 + O2 → 2H2O
(⇌): Represents a reversible reaction.
In the above reaction, P4O10 & water are reactants and Phosphoric acid is the product.
Rules for Writing Informative Chemical Equations
Write the correct chemical formulas for reactants and products.
Place reactants on the left and products on the right, separated by an arrow (→ or ⇌).
Include physical states using (s), (l), (g), or (aq).
Indicate special outcomes like gas evolution (↑) or precipitate (↓).
Specify reaction conditions (e.g., temperature, pressure, catalyst) above or below the arrow.
Balance the chemical equation correctly.
A word equation is a way to describe a chemical reaction using the names of the substances involved instead of their chemical formulas.
Here are the key rules for writing a word equation:
Example: Methane + Oxygen → Carbon Dioxide + Water
A balanced chemical equation has the same number of atoms of each element on both sides. The process to achieve this is known as the "hit-and-trial method," where we try various coefficients to balance the equation using the smallest whole numbers.
Here are the steps for balancing simple equations:
Step 1. Count the no. of atoms of various elements on both sides of the equation
Example: Fe + H2O → Fe3O4 + H2
Step 2. Start balancing with the compound which contains maximum number of atoms. It may be a reactant or product. In that compound select the element which has maximum number of atoms.
According to this rule Fe3O4 has maximum number of atoms & oxygen has 4 atoms so it is selected.
So the partly balanced equation is
Fe + 4H2O → Fe3O4 + H2
Step 3. Fe and H are not balanced in the above reaction so the above reaction repeat the above process for both i.e.
Now the equation becomes as
Fe + 4H2O → Fe3O4 + 4H2
Step 4. Balance the Iron atoms similarly.
Now the equation is
3Fe + 4H2O → Fe3O4 + 4H2
Step 5. Finally check the correctness of the balanced equation by counting the number of atoms on both sides of the equation.
Step 6. To make chemical equation more informative physical states of the reactants and products are mentioned as for solid (s), liquid (l), gas (g) and for aqueous solution of reactant or product (aq) is written.
Now the equation becomes as
3Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g)
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1. What is a chemical equation? | ![]() |
2. What are the rules for writing a word equation? | ![]() |
3. What are the steps to balance chemical equations? | ![]() |
4. Why is it important to include the symbols of physical states of substances in a chemical equation? | ![]() |
5. Can you provide a solved example of writing and balancing a chemical equation? | ![]() |