Rates of reaction

• Quantity of reactants or products in a chemical reaction

  Plotted on a graph against time
• Slope of the line on the graph

  Gives the rate of reaction
• Steep slope initially


  Reaction is fast
• Slope becomes less steep over time

  Reaction is slowing down
• Flat slope at the end


  Reaction has stopped
• Quantity of product


  Measured in grams or cm^3 (if a gas)
• Mean rate of reaction


  Quantity of product formed / time taken
• Calculating mean rate of reaction

  1. Quantity of product formed / time taken

  2. Quantity of reactant used / time taken
• Tangent


  A straight line that just touches the curve at a specific point
• Tangent


  • The slope of the tangent gives an idea of the rate of reaction at that point
  • The slope of the tangent is constantly changing, indicating the rate of reaction is also constantly changing
• Measuring rate of reaction using a tangent


  1. Draw a tangent at the point of interest

  2. Construct a triangle using the tangent

  3. Measure the vertical (Y) and horizontal (X) sides of the triangle

  4. Calculate the rate of reaction by dividing Y by X
• The slope of the tangent at the start of the reaction is steeper than the slope of the tangent later in the reaction, indicating the reaction is faster at the start
• Calculating the rate of reaction using a tangent: Y = 14 grams, X = 25 seconds, Rate = 14/25 = 0.56 grams per second