Measuring the rate of reaction

• How is the rate of reaction calculated?

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

  5 cm³ per second
• Why does the average rate of reaction not reflect the actual rate throughout the reaction?

  Because the reaction rate changes over time
• What does a steep curve on a reaction graph indicate?

  A high rate of reaction
• What happens to the rate of reaction as magnesium is used up?

  The rate of hydrogen production slows down
• What are the axes labeled on the reaction graph?

  X-axis: time, Y-axis: volume of hydrogen
• How do you calculate the mean rate of reaction over three minutes?

  Divide hydrogen produced by time in seconds
• How do you find the rate of reaction at a specific time?

  Calculate the gradient of the tangent at that point
• What is a tangent in the context of a reaction graph?

  A straight line that touches the curve
• How do you find the gradient of the tangent line?

  Change in volume divided by change in time
• What is the change in volume of hydrogen at two minutes?

  Approximately 600 cm³
• If the change in time is 2 minutes 50 seconds, what is it in seconds?

  170 seconds
• What is the rate of reaction at two minutes?

  3.53 cm³ per second
• What should you do if your tangent is not perfect?

  Examiners allow a small range of values
• What does the graph of magnesium remaining against time show?

  It starts with the initial grams used
• How do you find the rate of reaction at one minute using the magnesium graph?

  Draw a tangent and calculate the gradient
• What is the change in magnesium at one minute?

  Approximately 0.72 grams
• If the change in time is 1 minute 40 seconds, what is it in seconds?

  100 seconds
• What is the rate of reaction calculated from the magnesium graph?

  0.0072 grams per second
• What happens if you use different y and x values for your tangent?

  You will still get the same answer
• What are the steps to calculate the mean rate of reaction from a graph?

  1. Identify the time interval on the x-axis.
  2. Draw a dashed line to intersect the curve.
  3. Find the corresponding volume on the y-axis.
  4. Divide the volume by the time in seconds.
• What are the steps to calculate the actual rate of reaction at a specific time?

  1. Identify the specific time on the x-axis.
  2. Draw a tangent line at that point.
  3. Calculate the gradient of the tangent.
  4. Use the formula: gradient = change in y / change in x.
• What are the characteristics of the reaction graph for magnesium and hydrochloric acid?

  • Starts steep due to high reactant availability.
  • Gradually flattens as reactants are consumed.
  • Indicates changing rates of reaction over time.