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CBSE · Class 7 · Science

Changes Around Us: Physical and Chemical

Standard difficulty · 20 questions · 40 marks

Name: Date: Score: ____ / 40

Show your working for Sections B and C. Answers are on the last page — try every question first!

Section A — Choose the correct answer8 × 1 = 8 marks
1.
A change in which no new substance is formed is a:
  1. neutralisation
  2. combustion
  3. chemical change
  4. physical change
2.
Which of these is a CHEMICAL change?
  1. souring of milk into curd
  2. grinding wheat
  3. deflating a balloon
  4. breaking glass
3.
Which of these is a PHYSICAL change?
  1. making popcorn
  2. rusting of iron
  3. dissolving sugar in water
  4. burning paper
4.
Which of these changes can be REVERSED?
  1. melting ice
  2. chopping vegetables
  3. making popcorn
  4. setting curd
5.
Which of these will turn lime water milky?
  1. the mixture of lemon juice and vinegar
  2. baking soda in plain water
  3. air we breathe out
  4. vinegar with salt
6.
Pouring water on burning wood puts out the fire by removing:
  1. carbon dioxide
  2. smoke
  3. heat
  4. fuel
7.
A candle under a 250 mL glass went out after 21 seconds. About how long might it burn under a 750 mL glass, which holds 3 times as much air?
  1. 24 s
  2. 21 s
  3. 63 s
  4. 73 s
8.
A pebble of 900 g loses about 2 g each year by weathering and erosion. How much will it lose in 50 years?
  1. 100 g
  2. 10 g
  3. 52 g
  4. 1,000 g
Section B — Short answer8 × 2 = 16 marks
9.
What is the difference between a physical and a chemical change?
10.
Is it a "physical" or "chemical" change? (a) cooking an egg (b) baking soda fizzing with vinegar
11.
Can it be reversed? Write "yes" or "no": (a) folding a cloth (b) burning wood
12.
Will it turn lime water milky? Write "yes" or "no": (a) tap water (b) the mixture of lemon juice and vinegar
13.
Which part of the fire triangle (fuel, oxygen or heat) does each remove? (a) turning off the gas supply to a burning stove (b) wrapping a woollen blanket round burning clothes
14.
Each spoon of baking soda used in a fizz test weighs 6 g. A class does 6 tests with 2 spoons each. How much baking soda is used?
15.
A candle weighed 56 g before burning and 13 g after. How much wax was used up? Is the burning a physical or a chemical change?
16.
Curd took 20 hours to set in winter and 10 hours in summer. How many hours faster in summer? Is setting of curd physical or chemical?
Section C — Word problems4 × 4 = 16 marks
17.
Explain the physical and chemical changes in a burning candle.
18.
Sort into physical and chemical changes, with a reason for one of each: souring of milk into curd, breaking glass, freezing water, rotting of food, cooking an egg, folding paper.
19.
Three set-ups pass these into lime water: (1) baking soda in plain water; (2) vinegar with salt; (3) air we breathe out. Which turn it milky, and what does that show? Name the substance that makes it milky.
20.
A candle burns 25 s under a small glass and 75 s under a glass three times as big. (a) Why does it go out? (b) Why does it last longer under the big glass? (c) Name the three things a fire needs. (d) How does a blanket put out a fire on clothes?
AmbifulWorksheets
Practice that never repeats
CBSE · Class 7 · Science

Answer key

Changes Around Us: Physical and Chemical · AW-7S-CHG-2026-V1 · For parents — fold back or tear off before handing the sheet to your child.

QAnswerWorking
1(d) physical change—
2(a) souring of milk into curd—
3(c) dissolving sugar in water—
4(a) melting ice—
5(c) air we breathe out—
6(c) heat—
7(c) 63 s21 × 3 = 63
8(a) 100 g2 × 50 = 100
9In a physical change no new substance forms; in a chemical change a new substance forms.—
10(a) chemical (b) chemical—
11(a) yes (b) no—
12(a) no (b) no—
13(a) fuel (b) oxygen—
1472 g6 × 2 × 6 = 72
1543 g; chemical (the wax vapour burns to form new substances; melting is physical)56 − 13 = 43
1610 hours; chemical20 − 10 = 10
17Physical: the wax melts, flows down and some evaporates into wax vapour. Chemical: the wax vapour burns with oxygen, giving heat, light, carbon dioxide and water vapour. So a burning candle shows both kinds of change.—
18Physical: breaking glass, freezing water, folding paper. Chemical: souring of milk into curd, rotting of food, cooking an egg. In a chemical change a new substance forms; in a physical change it does not.—
19(1) no change; (2) no change; (3) milky. Milky lime water shows carbon dioxide; the milkiness is calcium carbonate.—
20(a) It uses up the oxygen. (b) The big glass holds more air, so more oxygen. (c) Fuel, oxygen and heat. (d) It cuts off the oxygen.—