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CSEE (Form 4) Physical and Chemical Change — practice questions

Explore 4 free Physical and Chemical Change questions in CSEE (Form 4) Chemistry. Open each question or exercise to read its content, reference answers and available explanation.

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Physical and Chemical Change questions and exercises with answers

Showing questions 1–4 of 4.

Water is boiled and turns into steam. Why is this counted as a physical change?Read the answer and worked solution →What does the law of conservation of mass state about a chemical reaction?Read the answer and worked solution →During a chemical reaction, which of these quantities is not always conserved?Read the answer and worked solution →What does the law of constant composition say about different samples of the same compound?Read the answer and worked solution →

Worked practice questions

Water is boiled and turns into steam. Why is this counted as a physical change?

  1. Its mass falls by a little
  2. Its identity does not change
  3. New bonds form inside it
  4. It cannot ever be reversed
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Correct answer: B. Its identity does not change

1. In a physical change the particles themselves are not broken up. 2. Boiling moves the water molecules further apart but leaves each molecule whole. 3. During a physical change the form of matter may change but not its identity. 4. All changes of state are physical changes for this reason. _Source: Siyavula Physical Sciences Grade 10 (Everything Science, CC BY 4.0), Chapter 13: Physical and chemical change_

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What does the law of conservation of mass state about a chemical reaction?

  1. The total mass always rises
  2. The total mass always falls
  3. The total mass stays the same
  4. The number of molecules is fixed
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Correct answer: C. The total mass stays the same

1. Atoms are neither created nor destroyed when a reaction takes place, they are rearranged. 2. The law of conservation of mass says the total mass of the substances taking part is conserved during the reaction. 3. So the mass of the reactants equals the mass of the products. 4. The number of molecules is a different matter and can change, so that option is the trap here. _Source: Siyavula Physical Sciences Grade 10 (Everything Science, CC BY 4.0), Chapter 13: Physical and chemical change_

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During a chemical reaction, which of these quantities is not always conserved?

  1. The number of atoms
  2. The number of molecules
  3. The total mass present
  4. The kinds of atoms present
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Correct answer: B. The number of molecules

1. A reaction rearranges atoms into new groupings, it does not create or destroy them. 2. So the number of atoms of each kind is the same before and after. 3. Because the atoms are the same, the total mass is also the same. 4. The groupings themselves can change in number. 5. Two hydrogen peroxide molecules break down into two water molecules and one oxygen molecule. 6. That is two molecules turning into three, so the number of molecules is not conserved. 7. Assuming molecules must balance like atoms is the trap this item sets. _Source: Siyavula Physical Sciences Grade 10 (Everything Science, CC BY 4.0), Chapter 13: Physical and chemical change_

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