In-Depth Notes on Chemical Changes

Chapter 11: Chemical Changes

11.1 How Do We Identify A Chemical Change?

• Definition: A chemical change results in the formation of new substances.

• Identification: Changes can be observed through:

  • Color change

  • Gas production (bubbles or fumes)

  • Formation of a solid precipitate

  • Temperature changes (release or absorption of energy)

11.2 What Are The Different Types of Chemical Changes?

• Combustion: A substance combines with oxygen, producing heat and light.

  • Example: Burning of petrol in a car engine; produces carbon dioxide and water vapor.

• Decomposition: A substance breaks down into simpler substances.

  • Example: Heating sugar until it caramelizes produces carbon and water vapor.

• Oxidation: A substance reacts with oxygen.

  • Example: Iron rusting when exposed to moisture and air.

• Neutralization: An acid reacts with a base to form salt and water.

  • Example: Mixing hydrochloric acid with sodium hydroxide.

11.3 How Do Chemical Changes Occur?

• Interaction of Atoms: Atoms rearrange during chemical changes, forming new products.

  • Conservation of Mass: The mass of reactants equals the mass of products.

  • Example: In the reaction of hydrogen and nitrogen to form ammonia, the total mass remains the same.

• Heat Energy: Chemical reactions often involve energy changes; heat can be absorbed or released.

• Indicators: Use indicators like litmus paper to determine acidity or alkalinity and observe changes.

11.4 How Does The Knowledge Of Chemical Reactions Help Us In Our Daily Lives?

• Use of Acids and Bases: Knowledge of chemical reactions helps in practical applications:

  • Cleaning: Use of baking soda (an alkali) for removing stains.

  • Cooking: Understanding the role of baking powder (acid + carbonate) in bread-making.

  • Medicine: Antacids neutralize stomach acid to relieve discomfort.

• Environmental Impact: Awareness of chemical reactions informs us about acid rain, pollution, and its effects on health and the environment.

18.1 Chemical Changes as a Result of Interactions

• Physical vs. Chemical Change: A physical change does not form new substances (e.g., melting ice). A chemical change does form new substances (e.g., rusting iron).

• Word Equations: Represent chemical reactions using word equations, showing reactants and products.

  • Example: Sodium + Chlorine → Sodium Chloride

• Examples: Forming plastics from crude oil; combustion of charcoal produces heat and light.

18.2 Types of Chemical Changes

• Combustion: The burning of fuels.

  • Releases energy, producing various gases.

• Thermal Decomposition: Heat breaks down substances into simpler products.

  • Example: Heating limestone to produce calcium oxide and carbon dioxide.

• Oxidation: Interaction with oxygen.

  • Rusting: Oxidation of iron.

• Cellular Respiration: A type of oxidation occurring in living organisms to release energy.

18.3 Test Your Understanding

• Is "ice melting" a physical or chemical change?

  • Answer: Physical change; no new substance is formed.

• Reaction of acids with metals leads to the production of hydrogen gas and salt.

• The interpretation of pH indicators and their application in testing substances.

Applications of Chemical Changes

• Combatting Acid Rain: Understanding chemical reactions leads us to solutions for mitigating acid rain's impact on environments and structures.

• Preventing Rusting: Strategies include coating metals with paint, oil, or galvanizing to protect against oxidation.

• Everyday Products: Insight into chemical changes informs product use, from cleaning supplies to food science.

• Environmental Awareness: Knowledge of harmful chemical reactions helps mitigate their effects, promoting sustainability.

Reactions of Acids:

• Acid + Akali —> salt water

• Acid + Metal —> salt + hydrogen

• Acid + Carbonates —> salt + water + carbon dioxide
  

Types of chemical reaction

• Neutralication (Acid + ALkali)

• Acid + Metals

• Acid + Carbonates

• Combusiton eg: Carbon+Oxygen—Heat—> Carbon Dioxide

• Thermal Decomposition eg: Sugar —-Heat—> carbon + water vapour

• Oxidation eg: sugar + oxygen —> carbon dioxide + water vapour / eg: iron + oxygen —-> rust