CIE iGCSE Co-Ordinated Science C6.2 Rate of reaction Exam Style Questions Paper 1
▶️ Answer/Explanation
To increase the rate of reaction, we need to increase the frequency of successful collisions between reactant particles. According to collision theory, the rate can be increased by:
- Increasing the concentration of the acid (more HCl particles per unit volume, leading to more frequent collisions with CaCO\(_3\)).
- Increasing temperature (particles have more kinetic energy, leading to more frequent and more energetic collisions).
- Decreasing particle size of solid reactants (increases surface area).
- Adding a catalyst.
Looking at each option:
- A. Decreasing temperature decreases the rate (less kinetic energy).
- B. Increasing particle size of calcium carbonate decreases the surface area, which decreases the rate.
- C. Increasing the concentration of the acid increases the rate because there are more acid particles in the same volume, leading to more frequent collisions.
- D. Increasing the volume of the acid does not increase the rate unless the concentration is also increased. The rate depends on concentration, not on total volume.
Therefore, the correct option is C.
✅ Answer: (C)
▶️ Answer/Explanation
Increasing concentration increases the number of particles per unit volume, leading to more frequent collisions.
Increasing temperature gives particles more kinetic energy, leading to more effective collisions.
Increasing volume (with same concentration) does not change rate, and larger pieces decrease surface area, reducing rate.
✅ Answer: (A)
Increasing temperature gives particles more kinetic energy, leading to more effective collisions.
Increasing volume (with same concentration) does not change rate, and larger pieces decrease surface area, reducing rate.
✅ Answer: (A)
▶️ Answer/Explanation
Adding a catalyst, increasing concentration, and increasing temperature all increase the rate of reaction. However, decreasing the surface area of zinc reduces the area available for collisions with acid particles, which decreases the rate of reaction. Therefore, option D does not increase the rate.
✅ Answer: (D)
✅ Answer: (D)
▶️ Answer/Explanation
A balance is essential to record the decreasing mass of the flask and its contents as carbon dioxide escapes.
A stop-clock is essential to record the time at which each mass reading is taken.
Pipettes and thermometers are not needed, since volume transfer and temperature are not being measured here.
✅ Answer: (B)
A stop-clock is essential to record the time at which each mass reading is taken.
Pipettes and thermometers are not needed, since volume transfer and temperature are not being measured here.
✅ Answer: (B)
▶️ Answer/Explanation
Diluting the acid with water lowers the acid concentration, which reduces collision frequency and slows the reaction.
Using larger lumps of magnesium carbonate gives a smaller surface area, which also reduces collision frequency and slows the reaction.
The slowest experiment is the one combining both the most dilute acid and the largest (least reactive) particle size.
✅ Answer: (C)
Using larger lumps of magnesium carbonate gives a smaller surface area, which also reduces collision frequency and slows the reaction.
The slowest experiment is the one combining both the most dilute acid and the largest (least reactive) particle size.
✅ Answer: (C)