How to calculate the rate of reaction

• What can graphs be used to 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
• If 1200 cm³ of hydrogen is produced in 4 minutes, what is the rate?

  240 cm³ per second
• What does the average rate of reaction represent?

  Rate during the entire time period measured
• Why does the reaction rate slow down over time?

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

  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 three minutes?

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

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

  A line that touches the curve at one point
• 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 cm³ and time is 170 seconds, what is the rate?

  3.53 cm³ per second
• What is the significance of the examiners' allowance for tangent estimation?

  They accept answers within a small range
• How would you find the rate of reaction using magnesium remaining against time?

  Draw a tangent and calculate the gradient
• If the change in magnesium is 0.72 grams over 100 seconds, what is the rate?

  0.0072 grams per second
• What happens if you adjust the length of your tangent line?

  It still gives the same answer if steep
• What are the steps to calculate the mean rate of reaction from a graph?

  1. Identify the time period 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 rate of reaction at a specific time using a tangent?

  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 change in y over change in x for the rate.
• What does a graph of magnesium remaining against time look like?

  • Starts with initial mass (e.g., 1.2 grams)
  • Declines rapidly at first
  • Slows down as reaction progresses