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Olympiad (Class 7) Physical and chemical changes — practice questions

Explore 46 free Physical and chemical changes questions in Olympiad (Class 7) Science. Open each question or exercise to read its content, reference answers and available explanation.

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Physical and chemical changes questions and exercises with answers

Showing questions 1–30 of 46.

A physical change differs from a chemical change as in it theRead the answer and worked solution →Salt is dissolved in water and the water is then allowed to evaporate. What is left behind?Read the answer and worked solution →Iodine changes directly from a solid to a gas on warming. This process is calledRead the answer and worked solution →An iron nail rubbed with a magnet becomes a magnet itself. This is aRead the answer and worked solution →A mixture of sand and water can be separated byRead the answer and worked solution →Two volatile liquids such as alcohols are mixed. They can be separated byRead the answer and worked solution →Diamond and graphite are both forms of carbon. Their different appearance comes from differentRead the answer and worked solution →A steel blank is repeatedly heated and hammered to form a knife blade. This changes the steel'sRead the answer and worked solution →Which of these is a sign that a chemical change may have happened?Read the answer and worked solution →In a chemical reaction, the starting substances are calledRead the answer and worked solution →Compared with the reactants, the products of a chemical reaction usually haveRead the answer and worked solution →A reaction that gives out heat to the surroundings is calledRead the answer and worked solution →A reaction that needs heat to be supplied in order to occur is calledRead the answer and worked solution →Which sign tells that a solid has formed inside a liquid during a reaction?Read the answer and worked solution →A reaction goes faster on heating becauseRead the answer and worked solution →In a synthesis reaction, simple substances combine to giveRead the answer and worked solution →Water is split by electricity into hydrogen and oxygen. This is aRead the answer and worked solution →An iron nail dipped in copper sulphate solution turns brown as iron replaces copper. This isRead the answer and worked solution →In a double displacement reaction, the two compoundsRead the answer and worked solution →Burning a fuel in oxygen with release of heat and light is calledRead the answer and worked solution →A candle burns: wax melts, then the wick burns. Which is true?Read the answer and worked solution →Precipitation in chemistry means the formation ofRead the answer and worked solution →During photosynthesis, plants use sunlight to turn carbon dioxide and water into glucose andRead the answer and worked solution →A catalyst takes part in a reaction but at the end it isRead the answer and worked solution →Two solids react very slowly. Which step speeds the reaction up?Read the answer and worked solution →Rust is mainly a reddish-brown compound of iron withRead the answer and worked solution →Rusting of an iron nail needs both oxygen andRead the answer and worked solution →An iron nail is kept in dry air with no water at all. It willRead the answer and worked solution →Iron gates near the sea rust faster than those far inland because seawater hasRead the answer and worked solution →Rusting is called a chemical change becauseRead the answer and worked solution →

Worked practice questions

A physical change differs from a chemical change as in it the

  1. mass of matter rises
  2. substance turns into gas
  3. composition stays the same
  4. colour always stays put
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Correct answer: C. composition stays the same

A physical change alters form or state only, so the same substance remains with the same composition.

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Salt is dissolved in water and the water is then allowed to evaporate. What is left behind?

  1. A new gas
  2. Sugar crystals
  3. A new acid
  4. Solid salt
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Correct answer: D. Solid salt

Dissolving is a physical change, so evaporating the water leaves the original salt behind.

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Iodine changes directly from a solid to a gas on warming. This process is called

  1. condensation
  2. freezing
  3. fusion
  4. sublimation
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Correct answer: D. sublimation

A solid turning straight into a gas without becoming liquid is sublimation, a physical change.

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