Rate of Reaction & Chemical Equilibrium is one of 10 topics in the Grade 12 Physical Sciences CAPS syllabus, covered across 4 lessons on Study Vault. Below are real practice questions from this topic with full worked answers.
Sample practice questions
Easy
1. Reaction rate is defined as:
The change in concentration of a reactant or product per unit time
The total amount of product formed
The time taken for a reaction to start
The temperature at which a reaction occurs
Answer: The change in concentration of a reactant or product per unit time — Rate=ΔtΔ[concentration], typically in mol⋅dm−3⋅s−1.
Medium
2. In an experiment, the concentration of a reactant drops from 0.80 mol⋅dm−3 to 0.50 mol⋅dm−3 over 60 seconds. Calculate the average rate in mol⋅dm−3⋅s−1 (give your answer to 3 decimal places).
3. In the reaction between Na2S2O3 and HCl, a cross drawn under the flask becomes invisible due to a sulfur precipitate forming. A faster reaction is indicated by:
A shorter time for the cross to disappear
A longer time for the cross to disappear
No change in the time observed
A colour change instead of a precipitate
Answer: A shorter time for the cross to disappear — A shorter time to reach the same amount of product (enough precipitate to obscure the cross) means the reaction proceeded faster.
