Measuring rates of a reaction from a graph

• What can graphs measure in a reaction?

  Mean rate and rate at specific time
• How is the rate of reaction calculated?

  By dividing reactants used or products formed by time
• What is the rate of reaction if 1200 cm³ of hydrogen is produced in 4 minutes?

  5 cm³ per second
• Why does the reaction rate slow down over time?

  Reactants are used up during the reaction
• What does a steep curve on a graph indicate?

  A high rate of reaction
• What happens to the graph once all magnesium is used up?

  The graph plateaus
• How do you calculate the mean rate of reaction over a period using a graph?

  • Find the time on the x-axis
  • Draw a dashed line to intersect the curve
  • Find the corresponding volume on the y-axis
  • Divide the volume by the time period
• How do you find the rate of reaction at a specific time?

  Calculate the gradient of the tangent
• What is a tangent in relation to a curve?

  A straight line that touches the curve
• How is the gradient of the tangent calculated?

  Change in y divided by change in x
• If the change in volume of hydrogen is 600 and change in time is 170 seconds, what is the rate?

  3.53 cm³ per second
• What is the significance of the tangent's length when calculating the rate?

  Longer tangents provide more accurate values
• How would you find the rate of reaction using a magnesium graph?

  • Start with initial grams of magnesium
  • Find the time point on the curve
  • Draw a tangent at that point
  • Calculate change in y and change in x
  • Divide change in y by change in x
• If the change in magnesium is 0.72 grams and change in time is 100 seconds, what is the rate?

  0.0072 grams per second
• What should you do if your tangent is not perfect?

  Examiners allow small range of values
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