Sign In Request Beta Access
← Back to Chemistry

GCSE Chemistry 05 — The Rate and Extent of Chemical Change

Public

Topics include Collision Theory Fundamentals, Methods for Measuring Rates of Reaction, Calculating Rates from Graphs, Effect of Surface Area on Rate, Effect of Concentration and Pressure, Effect of Temperature on Rate, Catalysts and Energy Profiles, and Reversible Reactions and Dynamic Equilibrium.

Chemistry EN
186 cards
Study this deck on Deckloop

Preview Cards

A sample of cards from this deck.

Example explainer

A sample of the AI explainer you can generate for cards in this deck.

Calculating Rates from Graphs

Interpreting reaction graphs and calculating gradients to determine rate at specific points.

Key points

  • Gradient = Rate: On a quantity vs. time graph, the gradient (slope) represents the rate.
  • Initial Rate: Draw a tangent at t=0t=0. This is usually the steepest part of the curve.
  • Instantaneous Rate: Draw a tangent at a specific time tt and calculate change in ychange in x\frac{\text{change in } y}{\text{change in } x}.
  • Curve Shape: Steepest at start (fastest), becomes less steep (slowing down), becomes horizontal (reaction stopped/equilibrium).
  • Anomalies: Points significantly off the line of best fit.

Worked example

Question

Calculate the rate at 20s from a graph where the tangent at 20s passes through points (10, 30) and (30, 70).

Solution

1. Identify coordinates on the tangent: (x1,y1)=(10,30)(x_1, y_1) = (10, 30) and (x2,y2)=(30,70)(x_2, y_2) = (30, 70).
2. Apply gradient formula: Gradient=70−3030−10=4020\text{Gradient} = \frac{70 - 30}{30 - 10} = \frac{40}{20}
3. Calculate result: 2.0 units/s2.0 \text{ units/s}

Common pitfalls

  • Calculating the average rate (total volume / total time) when asked for the rate at a specific time.
  • Drawing tangents that do not touch the curve at the correct point.
  • Thinking a horizontal line means the reaction is reversing (it means it has stopped or reached equilibrium).

Prerequisites

  • Plotting graphs
  • Calculating gradients (maths)
Further resources