Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Changes can be classified based on their speed into fast and slow changes. Slow changes take a long duration (days, months, or years) to complete.
A Physical Change is a change in the physical properties such as shape, size, or state, where no new substance is formed. Most are reversible. For example, the melting of glaciers over time.
A Chemical Change is a change in which one or more new substances with different properties are formed. These are usually irreversible. For example, the rusting of iron.
Rusting of Iron: A slow natural chemical change that occurs when iron is exposed to oxygen () and moisture () for a long time. The resulting substance is called rust ().
Weathering of Rocks: A very slow natural process where rocks break down into smaller particles to form soil due to the action of wind, water, and temperature changes.
Formation of Fossil Fuels: A slow chemical change occurring deep under the earth's crust over millions of years where dead organic matter is converted into coal or petroleum under high pressure and temperature.
Ripening of Fruits: A slow natural chemical change where the color, taste, and texture of the fruit change due to internal chemical reactions.
📐Formulae
💡Examples
Problem 1:
Identify the type of change: 'The growth of a seedling into a giant banyan tree.'
Solution:
It is a slow, natural, and irreversible chemical change.
Explanation:
Growth involves the formation of new cells and complex organic compounds through biological processes like photosynthesis, which cannot be reversed to get the seed back.
Problem 2:
Why is the rusting of an iron gate in coastal areas faster than in a desert?
Solution:
The presence of high humidity (moisture) and salt in coastal air accelerates the chemical reaction.
Explanation:
For rusting to occur, both oxygen () and water () are required. In coastal areas, the moisture content is significantly higher than in deserts, leading to a faster rate of rust formation.
Problem 3:
Calculate the total mass of the product if of Iron reacts with of Oxygen to form Iron Oxide (ignoring water mass).
Solution:
Explanation:
According to the Law of Conservation of Mass, the mass of reactants must equal the mass of the products: