The rate of reaction is the change in the amount of a reactant used up, or a product formed, per unit of time.
The rate of reaction is the change in the amount of a reactant used up, or a product formed, per unit of time. Malay: kadar tindak balas · Chinese: 反应速率.
The rate tells you how fast a chemical change happens. Because a reactant is consumed while a product builds up, you can follow the rate by measuring any quantity that changes during the reaction and dividing that change by the time taken. In SPM the quantity is usually a volume of gas collected, a loss in mass as gas escapes, or a change in the concentration or clarity of a solution. The unit therefore depends on what you measure: for example cm3 s−1 for a gas volume, or g s−1 for a change in mass.
Example. When marble chips react with dilute hydrochloric acid, carbon dioxide is released. If a gas syringe collects 48 cm3 of gas in 24 seconds, the average rate over that interval is 48 divided by 24, which is 2 cm3 s−1. A steeper climb on the volume-time graph means a faster rate at that moment.
Confusion to avoid. Do not mix up the rate with the total amount of product. Two reactions can give exactly the same final volume of gas yet have very different rates; the faster one simply reaches that volume sooner. The rate is about speed over time, not the size of the final yield, so an answer that quotes only the total volume has not described the rate at all.
Rate of reaction is the central idea of this whole chapter. Every factor you study, the collision theory and the action of a catalyst all explain why this rate speeds up or slows down, so getting the definition word-perfect matters throughout SPM Chemistry.
Want a teacher to make this click?
We teach SPM Chemistry one to one, so your child understands it and scores it.
from RM50/hr · One-hour paid trial · Same-day reply