Chemical Reaction

Chemical Change

A chemical change is a process in which substances combine or break apart to form new substances with different properties. These changes usually cannot be reversed by simple physical means.

Examples of Chemical Change 

1. Burning wood - Wood turns into ash, carbon dioxide, and water vapor. 

2. Rusting of iron - Iron reacts with oxygen and moisture to form rust (iron oxide). 

3. Cooking food - Ingredients undergo chemical changes to form new flavors and textures. 

4. Souring of milk - Milk turns sour due to the formation of lactic acid from lactose. 

5. Fireworks explosion - Chemical reactions produce light, sound, and gases. 

Chemical Reaction

The exchanges, combination, or decomposition that occurs in the molecules of substances during a chemical change is called chemical Reaction. The chemical change transforms one substance into another completely new. The chemical changes are represented by chemical reactions.

Reactants and Products

The substances that take part in a chemical reaction are called Reactants. The reactants are written on the left side of the chemical reaction.

The substances produced after the chemical change are called Products. The products are written on the right side of the chemical reaction.

Example:

Hydrogen gas(\(H_2\)) + Oxygen gas(\(O_2\)) \(\rightarrow\) Water (\(H_2O\))

Reactants : Hydrogen gas(\(H_2\)) + Oxygen gas(\(O_2\)) 

Products : Water (\(H_2O\))

Balanced Chemical Reactions

The chemical equation written by balancing the total number of atoms of each element in the reactant and product is called the balanced chemical reaction. A balanced chemical reaction has the same number of each type of atom on both sides of the equation. This ensures that the law of conservation of mass is satisfied, meaning no atoms are created or destroyed in the reaction.

Steps to Balance a Chemical Reaction

1. Write the Unbalanced Equation 

   Write down the chemical formulas of reactants and products. 

   Example: 

   \(\text{H}_2 + \text{O}_2 \rightarrow \text{H}_2\text{O}\)

2. List the Number of Atoms for Each Element 

   Count the atoms of each element on both sides of the equation. 

   Example: 

   - Reactants: H = 2, O = 2 

   - Products: H = 2, O = 1 

3. Balance the Atoms of One Element at a Time 

   Use coefficients to balance the number of atoms for one element. Start with elements that appear in only one reactant and one product. 

   Example: Add a coefficient of 2 to \(\text{H}_2\text{O}\):  

   \(\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O}\) 

4. Adjust Coefficients as Needed 

   If an element appears in multiple compounds, adjust coefficients to ensure the total number of atoms matches on both sides. 

   Example: Balance oxygen by adding a coefficient of 2 to \(\text{H}_2\): 

   \(2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O}\) 

5. Verify the Balance 

   Check that all elements have the same number of atoms on both sides. 

   - Reactants: H = 4, O = 2 

   - Products: H = 4, O = 2 

6. Simplify Coefficients if Necessary 

   Ensure the coefficients are in their simplest whole-number ratio.

Information Obtained from a Balanced Chemical Reaction 

1. Conservation of Mass: The total mass of reactants equals the total mass of products. 

2. Stoichiometric Ratios: The coefficients indicate the ratio in which reactants combine and products form. 

3. Nature of Reactants and Products: Shows the specific substances involved in the reaction. 

4. Energy Changes: Provides clues about whether the reaction is exothermic (releases energy) or endothermic (absorbs energy). 

5. State of Substances: Includes the physical states of reactants and products (solid, liquid, gas, aqueous). 

6. Quantitative Predictions: Allows calculation of quantities of reactants or products required or produced. 

Exothermic and Endothermic Reactions

1. Exothermic Reactions

Chemical reactions that produce heat are called exothermic reactions. Some examples are the digestion of food, Burning wood, and the reaction between water and Calcium oxide.

2. Endothermic Reactions

The chemical reactions that absorb heat are called exothermic reactions. Some examples are photosynthesis, evaporation of water, cooking food, and melting ice.