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Chapter Analysis
Beginner8 pages • EnglishQuick Summary
This chapter on Physical and Chemical Changes explores the differences between physical changes, which do not result in new substances and are generally reversible, and chemical changes, which result in the formation of new substances. Examples of physical changes include changes in state or shape, like ice melting or paper being cut. Chemical changes, in contrast, include processes like rusting and burning, often involving heat or color changes. The chapter also covers methods such as crystallization and galvanization to prevent corrosion and obtain pure substances.
Key Topics
- •Physical changes
- •Chemical changes
- •Rusting
- •Crystallization
- •Galvanization
- •Reversibility of changes
- •Formation of new substances
- •Environmental impact of changes
Learning Objectives
- ✓Differentiate between physical and chemical changes.
- ✓Understand the process of crystallization and its applications.
- ✓Identify everyday examples of physical and chemical changes.
- ✓Explain the factors affecting rusting and methods to prevent it.
- ✓Recognize the signs of chemical changes.
- ✓Explore applications of chemical changes in daily life.
Questions in Chapter
Classify the changes involved in the following processes as physical or chemical changes: (a) Photosynthesis (b) Dissolving sugar in water (c) Burning of coal (d) Melting of wax (e) Beating aluminium to make aluminium foil (f) Digestion of food
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State whether the following statements are true or false: (a) Cutting a log of wood into pieces is a chemical change. (b) Formation of manure from leaves is a physical change. (c) Iron pipes coated with zinc do not get rusted easily. (d) Iron and rust are the same substances. (e) Condensation of steam is not a chemical change.
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Fill in the blanks in the following statements: (a) When carbon dioxide is passed through lime water, it turns milky due to the formation of _________. (b) The chemical name of baking soda is _________. (c) Two methods by which rusting of iron can be prevented are _________ and _________. (d) Changes in which only _________ properties of a substance change are called physical changes. (e) Changes in which new substances are formed are called _________ changes.
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When baking soda is mixed with lemon juice, bubbles are formed with the evolution of a gas. What type of change is it? Explain.
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When a candle burns, both physical and chemical changes take place. Identify these changes. Give another example of a familiar process in which both the chemical and physical changes take place.
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How would you show that setting of curd is a chemical change?
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Explain why burning of wood and cutting it into small pieces are considered as two different types of changes.
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Describe how crystals of copper sulphate are prepared.
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Explain how painting of an iron gate prevents it from rusting.
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Explain why rusting of iron objects is faster in coastal areas than in deserts.
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Additional Practice Questions
What is a chemical change?
easyAnswer: A chemical change involves a transformation that results in the formation of new substances. Examples include rusting, burning, and fermentation.
How can rusting be prevented?
mediumAnswer: Rusting can be prevented by applying paint or grease to iron surfaces, galvanization, or using stainless steel which contains chromium and is resistant to rust.
Describe the process of crystallization.
mediumAnswer: Crystallization is a process used to obtain pure substances. It involves dissolving a substance in water, filtering it, allowing the solution to cool, and then letting it form crystals.
Is the melting of ice a chemical or physical change? Explain.
easyAnswer: Melting of ice is a physical change because it involves a change in state from solid to liquid without forming any new substances.
Why is photosynthesis considered a chemical change?
mediumAnswer: Photosynthesis is a chemical change because it involves the conversion of carbon dioxide and water into glucose and oxygen through a series of chemical reactions.
Provide an example of a chemical change in everyday life.
easyAnswer: Cooking an egg results in a chemical change as the heat causes proteins to denature and form a new substance.
What changes occur when a magnesium ribbon burns?
mediumAnswer: When magnesium ribbon burns, it reacts with oxygen to form magnesium oxide, a new substance, releasing heat and light, indicating a chemical change.
Identify whether dissolving salt in water is a physical or chemical change and justify your answer.
mediumAnswer: Dissolving salt in water is a physical change because it's a reversible process that does not alter the chemical identity of salt.
What happens during the reaction between vinegar and baking soda?
easyAnswer: When vinegar reacts with baking soda, carbon dioxide gas is released, and new substances are formed, indicating a chemical change.
Compare and contrast a physical change with a chemical change.
hardAnswer: A physical change does not form new substances and is often reversible, e.g., melting ice. A chemical change results in new substances, often irreversible, e.g., rusting iron.
NCERT Exemplar
AvailablePractice with NCERT Exemplar problems and solutions for this chapter. Exemplar problems are designed to help you master the concepts with advanced-level questions.
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