In-Depth Notes on Chemical Changes

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)

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.

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.

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.

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.

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.

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.

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.

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