GCSE Combined Science (AQA)

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Calculating Rate from Graphs

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The rate and extent of chemical change Rate of reaction

Calculating Rate from Graphs

7:05 Calculating Reaction Rates using Graphs
Spec 4.6.1.1
Previous Rate Changes & Graphs Next Collision Theory & Reaction Rate
  • The rate of a reaction changes as the reaction progresses.
  • Rate measures how quickly reactants are used up or products are made.
  • A rate of reaction graph can measure the rate at a specific time.
  • Example: Gas product collected in a syringe, timed with a stopwatch, and volume measured at regular intervals.
  • Plot a graph with volume on the y-axis and time on the x-axis, resulting in a curve.
  • Most gas is produced early, with the reaction slowing down towards the end.
  • The rate of reaction at a given time is the gradient of the curve at that point.
  • Calculate the gradient of a graph to determine its steepness.
  • For curved reaction graphs, calculate the gradient of the tangent to the curve.
  • A tangent is a line that just touches the curve and has the same gradient at that point.
  • The steeper the line, the bigger the gradient, indicating a faster reaction.
  • Use gradients to calculate rates of reaction from graphs in exams.
  • Steps to calculate gradient:
  • 1. Identify a point in time and mark it on the graph.
  • 2. Draw a tangent line using a ruler, ensuring it just touches the curve.
  • 3. Choose distant points on the tangent line that are easy to read on both axes.
  • 4. Calculate the change in the y-axis and x-axis between the points.
  • 5. Use these changes to calculate the gradient.
  • Gradient formula: Gradient = Change in Y / Change in X.
  • Example calculation: Change in Y = 20, Change in X = 105, Gradient = 0.19.
  • Rate of reaction is equal to the gradient.
  • Determine units for the rate of reaction by dividing units of the y-axis by the x-axis.
  • Example units: Centimeters cubed per second (cm��/s).

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