Changes Around Us: Physical and Chemical – Very Short Answer Type Questions

Class 7 Science — Chapter 5 Very Short Answer Questions

50 Very Short Answer Questions & Answers

Q1: What is a physical change?
A: A change in which the form or state of a substance changes but its chemical identity remains the same.
Q2: What is a chemical change?
A: A change in which new substances with different properties are formed.
Q3: Give one example of a physical change.
A: Melting of ice into water.
Q4: Give one example of a chemical change.
A: Rusting of iron.
Q5: What does reversible change mean?
A: A change that can be undone by simple physical processes (e.g., water freezing and melting).
Q6: What is meant by irreversible change?
A: A change that cannot be easily reversed (e.g., burning paper).
Q7: Is boiling of water physical or chemical?
A: Physical change.
Q8: Is digestion of food a physical or chemical change?
A: Chemical change.
Q9: Name one sign that a chemical change has occurred.
A: Evolution of a gas (bubbles).
Q10: Can dissolving sugar in water be reversed?
A: Yes — by evaporation; it is typically a physical change.

Q11: What change in temperature may indicate a chemical reaction?
A: A temperature change — either heat released (exothermic) or absorbed (endothermic).
Q12: Does colour change always mean a chemical change?
A: Not always; it is a sign but should be confirmed with other observations.
Q13: What does formation of a precipitate indicate?
A: Formation of an insoluble solid when two solutions react — a chemical change.
Q14: What is effervescence?
A: Rapid bubbling or fizzing due to gas evolution during a chemical reaction.
Q15: Is emission of light a sign of chemical change?
A: Yes — e.g., burning magnesium emits bright light.
Q16: What simple test indicates hydrogen gas?
A: The 'pop' test with a burning splint.
Q17: Does formation of bubbles always mean chemical change?
A: Usually yes in reactions, but boiling (physical) also forms bubbles; context matters.
Q18: What sign is seen when iron rusts?
A: Colour change to reddish-brown and flaky oxide formation.
Q19: What does smell or odour change indicate?
A: Possible chemical change (new substances with different smells formed).
Q20: Name a reaction where gas evolution is obvious.
A: Vinegar (acetic acid) reacting with baking soda (sodium bicarbonate) produces carbon dioxide.

Q21: Is cutting a paper physical or chemical?
A: Physical change (shape altered; same substance).
Q22: Is melting of butter reversible?
A: Yes — solidifies on cooling; physical change.
Q23: Is burning of wood reversible?
A: No — chemical change; cannot get original wood back.
Q24: Is formation of curd from milk physical or chemical?
A: Chemical change (new substance and properties formed).
Q25: Is evaporation of alcohol physical or chemical?
A: Physical change (change of state).
Q26: Is ripening of fruit a physical or chemical change?
A: Chemical change (enzymatic reactions produce new substances).
Q27: Is dissolving salt in water reversible?
A: Yes — by evaporating water; physical change.
Q28: Is cooking an egg physical or chemical change?
A: Chemical change (proteins denature and new substance forms).
Q29: Is stretching a rubber band physical or chemical?
A: Physical change (shape change; elastic return when released).
Q30: Is dissolving gas in a soda a physical or chemical process?
A: Physical process (gas dissolved; released on opening).

Q31: Give one example of chemical change in household.
A: Cooking food (e.g., making chapati).
Q32: Give one example of physical change in household.
A: Ice melting in the refrigerator.
Q33: Why is rusting harmful?
A: It weakens iron objects, causing damage and economic loss.
Q34: How can rusting be prevented?
A: Painting, oiling, galvanisation, or alloying (e.g., stainless steel).
Q35: Is formation of soap from oil chemical or physical?
A: Chemical change (saponification produces new substances).
Q36: Is shredding vegetables physical or chemical?
A: Physical change (only size/shape altered).
Q37: What happens chemically when food is digested?
A: Large molecules break down into simpler substances via enzymatic chemical reactions.
Q38: Is burning of fossil fuels a physical or chemical change?
A: Chemical change (combustion produces CO₂, H₂O and releases energy).

Q39: What is observed when magnesium ribbon burns?
A: Bright white flame and white ash (magnesium oxide) — chemical change.
Q40: What is observed when dilute acid reacts with zinc?
A: Bubbling due to hydrogen gas and zinc dissolving — chemical change.
Q41: What does mixing barium chloride and sodium sulfate show?
A: White precipitate of barium sulfate forms — chemical change (precipitation).
Q42: What indicates an exothermic reaction?
A: The temperature of the surroundings increases (heat released).
Q43: What indicates an endothermic reaction?
A: The surroundings become colder (heat absorbed).
Q44: Why does mixing vinegar and baking soda fizz?
A: They react to produce CO₂ gas causing effervescence — chemical change.

Q45: State one difference between physical and chemical change.
A: Physical change does not form new substances; chemical change does.
Q46: Can physical changes involve energy changes?
A: Yes — e.g., melting absorbs heat; but composition remains same.
Q47: Is bleaching a chemical or physical change?
A: Chemical change (changes the colour by chemical reaction).
Q48: Why should multiple signs be used to identify chemical change?
A: Because a single sign (like bubbling) may also occur in physical processes; multiple signs increase confidence.
Q49: Is freezing water an indication of chemical change?
A: No — freezing is a physical change (state change).
Q50: Give one tip to write short answers about changes in exams.
A: State the change type, mention 1–2 observations (signs), and conclude with a reason (example: "This is a chemical change because...").