Chemical Reactions Important points 2023 - 24

A chemical reaction is a process in which one or more substances (reactants) are transformed into different substances (products), exhibiting changes in their chemical composition and properties. 

Chemical Reactions (J K Online Classes)

Definition: A chemical reaction is a process where substances combine to form new substances with different properties.

Few important points:

- During a chemical reaction, bonds between atoms are broken and new bonds are formed, resulting in the creation of entirely different molecules. 

- The total mass of the reactants is always equal to the total mass of the products, as dictated by the law of conservation of mass.

Key Points:

1. Reactants: These are the substances that react with each other to form new substances. For example:

   - Example: In the reaction between hydrogen gas (H₂) and oxygen gas (O₂) to form water (H₂O), hydrogen and oxygen are the reactants.

2. Products: The new substances formed as a result of the reaction are called products.

   - Example: In the same reaction, water (H₂O) is the product.

3. Chemical Equations: These represent chemical reactions using symbols and formulas.

   - Example: The equation for the formation of water from hydrogen and oxygen is: 2H₂ + O₂ → 2H₂O

4. Types of Reactions:

   - Synthesis or Combination: When two or more substances combine to form a single compound.

     - Example: \(2H₂ + O₂ → 2H₂O\) (formation of water)

   - Decomposition: When a compound breaks down into simpler substances.

     - Example: \(2H₂O → 2H₂ + O₂\) (breakdown of water into hydrogen and oxygen)

   - Single Replacement: When an element reacts with a compound, displacing another element from it.

     - Example: \(Zn + 2HCl → ZnCl₂ + H₂\) (zinc displacing hydrogen in hydrochloric acid)

   - Double Replacement: When parts of two compounds switch places to form two new compounds.

     - Example: \(AgNO₃ + NaCl → AgCl + NaNO₃\) (silver nitrate and sodium chloride exchange ions)

   - Combustion: When a substance reacts with oxygen, often producing heat and light.

     - Example: \(CH₄ + 2O₂ → CO₂ + 2H₂O\) (methane burning in oxygen)

5. Factors Affecting Reactions:

   - Temperature: Higher temperatures often increase the rate of reactions.

   - Concentration: Higher concentrations of reactants can speed up reactions.

   - Catalysts: These are substances that speed up reactions without being consumed.

   - Surface Area: Finely powdered substances react faster due to increased surface area.

6. Conservation of Mass: In a chemical reaction, the total mass of the products is equal to the total mass of the reactants.

   - Example: In any balanced chemical equation, the number of atoms of each element on both sides of the equation remains the same.

7. Chemical Reactions in Nature

Nature is full of chemical reactions that occur constantly, influencing everything from the growth of plants to the functioning of our bodies. Here are some examples of chemical reactions in nature:

a) Photosynthesis: This vital process occurs in plants where they use sunlight, water, and carbon dioxide to produce glucose (a type of sugar) and oxygen.

   - Chemical Equation: \(6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂\)

b) Respiration: Both plants and animals undergo respiration, where they use oxygen to break down glucose and release energy, carbon dioxide, and water.

   - Chemical Equation: \(C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy\)

c) Rusting: The oxidation of iron in the presence of moisture and oxygen leads to the formation of iron oxide (rust).

   - Chemical Equation: \(4Fe + 3O₂ + 6H₂O → 4Fe(OH)₃\)

d) Digestion: In the human body, food undergoes various chemical reactions in the digestive system to break down complex molecules into simpler ones for absorption.

   - Chemical Reaction: Various reactions involving enzymes breaking down carbohydrates, proteins, and fats into simpler compounds.

e) Fermentation: Yeast and some bacteria carry out fermentation, converting sugars into alcohol and carbon dioxide in the absence of oxygen.

   - Chemical Equation for Alcohol Fermentation: \(C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂\)

f) Acid-Base Reactions: Natural occurrences like the neutralization of acids and bases in soil to maintain a pH suitable for plant growth involve chemical reactions.

   - Chemical Equation for Neutralization: \(HCl + NaOH → NaCl + H₂O\)

g) Weathering: Chemical reactions occur in rocks due to exposure to elements like water and carbon dioxide, leading to their breakdown over time.

   - Chemical Reaction: Various reactions like carbonation, hydration, and hydrolysis contribute to the breakdown of rocks.

These examples illustrate how chemical reactions are fundamental to numerous natural processes, sustaining life and shaping the world around us.

Understanding chemical reactions is crucial as they explain how substances change and combine, influencing everything from cooking to industrial processes.

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