Grade 10 · CAPS

Grade 10 Physical and Chemical Change

Physical Sciences practice questions and a worked example

Grade 10 physical and chemical change covers how matter changes and how reactions are written. The questions here ask you to tell physical from chemical changes, identify decomposition and synthesis reactions, write and balance chemical equations with phases, and use the law of constant composition in a calculation. They come from the DBE Grade 10 common Paper 2 for November 2016, 2017 and 2018, each with the answer from the marking guideline.

Worked example

The unbalanced chemical equation (i) and the word equation (ii) for two chemical reactions are shown below. (i) Cℓ₂(g) + H₂(g)→ HCℓ(g) (ii) aluminium carbonate → aluminium oxide + carbon dioxide 6.4 Write a balanced chemical equation for equation (i).

Answer & explanation

Cl₂(g) + H₂(g) → 2HCl(g)
To balance the chemical equation, we need to ensure that the number of each type of atom is the same on both sides of the equation. 1. Start with the given unbalanced equation: Cl₂(g) + H₂(g) → HCl(g). 2. Count the number of chlorine and hydrogen atoms on each side. On the left, there are 2 chlorine atoms and 2 hydrogen atoms. On the right, there is 1 chlorine atom and 1 hydrogen atom in HCl. 3. To balance the chlorine atoms, place a coefficient of 2 in front of HCl: Cl₂(g) + H₂(g) → 2HCl(g). 4. Now, there are 2 chlorine atoms and 2 hydrogen atoms on both sides of the equation. The balanced chemical equation is Cl₂(g) + H₂(g) → 2HCl(g).

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Physical and Chemical Change

Question 1 of 3

1.8 Consider the unbalanced chemical equation below. P₄(s) + H₂(g) → PH₃(g) Which ONE of the sets of coefficients will balance the chemical equation?
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More practice questions

Explore additional Grade 10 Physical and Chemical Change questions.

  • 2
    The unbalanced chemical equation (i) and the word equation (ii) for two chemical reactions are shown below. (i) Cℓ₂(g) + H₂(g)→ HCℓ(g) (ii) aluminium carbonate → aluminium oxide + carbon dioxide 6.2 What does the (g) in reaction (i) represent?
  • 3
    The unbalanced chemical equation (i) and the word equation (ii) for two chemical reactions are shown below. (i) Cℓ₂(g) + H₂(g)→ HCℓ(g) (ii) aluminium carbonate → aluminium oxide + carbon dioxide 6.3 Write down the chemical formulae for the following:
    6.3.1 Aluminium carbonate
  • 4
    The unbalanced chemical equation (i) and the word equation (ii) for two chemical reactions are shown below. (i) Cℓ₂(g) + H₂(g)→ HCℓ(g) (ii) aluminium carbonate → aluminium oxide + carbon dioxide 6.3 Write down the chemical formulae for the following:
    6.3.2 Aluminium oxide
  • 5
    Hydrogen peroxide decomposes at room temperature according to the following balanced chemical equation: 2H₂O₂(aq) → O₂(g) + 2H₂O(ℓ) 5.1 What does the (aq) represent in the equation above?

Common mistakes

  • Calling a phase change a chemical change. Melting, boiling and sublimation are physical changes; no new substance forms.
  • Changing subscripts to balance an equation. Only the coefficients in front of the formulae may change.
  • Leaving out the phases when the question asks for them: (s), (ℓ), (g) or (aq).

More Grade 10 Physical Sciences topics

Aligned to CAPS Grade 10 Physical Sciences — Physical and Chemical Change. Curriculum source: CAPS for the FET Phase, Department of Basic Education.

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