Rate graphs, average rate and initial rate
≈ 50 minRate graphs, average rate and initial rate
A rate graph records chemical change against time. For a product-concentration or gas-volume graph, an upward slope shows product forming; for a reactant-concentration graph, a downward slope shows reactant being used. Average rate is total change divided by total time over a stated interval. Initial rate is the gradient at the start, often found from a tangent, and is useful when reactant concentrations are known most clearly. A steep gradient means a large rate magnitude; a flat line means no measurable net change for that graph. Always include units such as mol dm⁻³ s⁻¹ or cm³ s⁻¹.
Work it through
A reactant concentration falls from 0.80 to 0.20 mol dm⁻³ in 30 s. Its average disappearance rate magnitude is (0.80 − 0.20)/30 = 0.020 mol dm⁻³ s⁻¹. The graph slope itself is negative if reactant concentration is plotted, but a reported rate is usually stated as a positive magnitude with clear wording.
Mastery target
Read rate graphs, calculate average or initial rate from the appropriate change and explain why the graph becomes less steep as reactants are depleted.
What does a steeper product-volume versus time graph indicate?
Name the key chemistry term from Rate graphs, average rate and initial rate that best fits the explanation and visual model.
Reactant concentration falls from 0.80 to 0.20 mol dm⁻³ in 30 s. What is the average disappearance rate magnitude in mol dm⁻³ s⁻¹?
Which statement corrects a common misunderstanding in Rate graphs, average rate and initial rate?