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NSC / Matric Rate and Extent of Reaction — practice questions

Explore 5 free Rate and Extent of Reaction questions in NSC / Matric Chemistry. Open each question or exercise to read its content, reference answers and available explanation.

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Rate and Extent of Reaction questions and exercises with answers

Showing questions 1–5 of 5.

What does the average rate of a chemical reaction describe?Read the answer and worked solution →The same mass of marble reacts with acid faster as a powder than as large chips. Why?Read the answer and worked solution →How does a catalyst make a reaction go faster?Read the answer and worked solution →A reaction that gives off a gas is followed by weighing the flask over time. Why must the flask stay open?Read the answer and worked solution →Magnesium reacts with hydrochloric acid and 0.30 mol of hydrogen gas is collected in 2.5 minutes. What is the average rate of formation of hydrogen?Read the answer and worked solution →

Worked practice questions

What does the average rate of a chemical reaction describe?

  1. How much product can ever form
  2. How much heat the reaction gives
  3. How stable the products will be
  4. How fast reactants are used up
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Correct answer: D. How fast reactants are used up

1. A car rusts over years while a match burns in seconds, so reactions run at very different speeds. 2. The average rate measures how quickly the reactants are used, or how quickly the products form. 3. It is worked out as the number of moles used or formed divided by the total time in seconds. 4. How much product could form in total is the yield, which is a different question. _Source: Siyavula Physical Sciences Grade 12 (Everything Science, CC BY 4.0), Rate and Extent of Reaction_

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The same mass of marble reacts with acid faster as a powder than as large chips. Why?

  1. Powder has a larger total mass
  2. Powder has a larger surface area
  3. Powder has a higher concentration
  4. Powder has a higher temperature
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Correct answer: B. Powder has a larger surface area

1. Only the particles at the surface of a solid can meet the acid. 2. A large lump keeps most of its particles buried inside where the acid cannot reach them. 3. Grinding the same mass into powder exposes far more particles at the surface. 4. More exposed particles means more successful collisions each second, so the rate goes up. 5. The mass is stated to be the same in both cases, so the second option cannot be the reason. _Source: Siyavula Physical Sciences Grade 12 (Everything Science, CC BY 4.0), Rate and Extent of Reaction_

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How does a catalyst make a reaction go faster?

  1. It raises the activation energy
  2. It heats the reacting particles
  3. It lowers the activation energy
  4. It adds energy to each collision
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Correct answer: C. It lowers the activation energy

1. Activation energy is the minimum energy a collision needs before a reaction can proceed. 2. At any temperature only a fraction of the particles carry that much energy. 3. A catalyst offers an alternative pathway that needs less activation energy. 4. A larger fraction of the particles now clears the lower barrier, so the rate rises. 5. The average kinetic energy of the particles is unchanged, so heating the particles is not what a catalyst does. _Source: Siyavula Physical Sciences Grade 12 (Everything Science, CC BY 4.0), Rate and Extent of Reaction_

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More Chemistry topics

Organic MoleculesElectrochemical ReactionsAcids and BasesChemical EquilibriumThe Chemical Industry