• For linear graphs (i.e. graphs with a straight-line), the gradient is the same throughout
  • This makes it easy to calculate the rate of change (rate of change = change ÷ time)

   

• However, many?enzyme rate experiments?produce non-linear graphs (i.e. graphs with a?curved line), meaning they have an?ever-changing gradient
  • They are shaped this way because the?reaction rate?is?changing over time

   

• In these cases, a?tangent?can be used to find the?reaction rate?at any?one point?on the graph:
  • A tangent is a?straight line?that is drawn so it just?touches?the curve at a?single point
  • The?slope?of this tangent?matches?the slope of the?curve?at just that point
  • You then simply find the?gradient?of the straight line (tangent) you have drawn

   

• The?initial?rate of reaction is the rate of reaction at the?start?of the reaction (i.e. where?time = 0)

Step 1: Estimate the extrapolated curve of the graph

Step 2: Find the tangent to the curve at 0 seconds (the start of the reaction)

The tangent drawn in the graph above shows that?72 cm3?of product was produced in the first??20 seconds.Step 3: Calculate the gradient of the tangent?(this will give you the?initial rate of reaction):

Gradient = change in y-axis ÷ change in x-axis

Initial rate of reaction = 72 cm3?÷ 20 s

Initial rate of reaction =?3.6 cm3?s-1