Rate calculations for enzyme activitySpec 1.11
The rate of reaction tells you how fast a reaction is happening. It is a compound measure, because it combines an amount with a time.
The units depend on what you measure, for example cm³/s for a volume of gas, or g/min for a mass. If an experiment measures the time taken for a reaction to finish, such as the time for starch to disappear, the rate can be found as 1 ÷ time, with units of s⁻¹.
Calculating a rate
An enzyme produces 12 cm³ of gas in 40 seconds. Calculate the rate of reaction in cm³/s.
- rate = amount of product ÷ time
- 12 ÷ 40 = 0.3
Answer: 0.3 cm³/s
Quick check
What is the name of the part of an enzyme that the substrate fits into?
Show answer
The active site.
Why does an enzyme stop working at a high temperature?
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The shape of the active site changes, so the substrate no longer fits. The enzyme is denatured.
Why does the rate level off as substrate concentration increases?
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All the active sites are occupied.
In the pH core practical, what colour shows that starch is still present with iodine solution?
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Blue-black.
Calculate the rate when 30 cm³ of gas is collected in 60 s.
Show answer
0.5 cm³/s.