Learning focus
Explain chemical changes using particles, collisions, equilibrium and electron transfer; interpret graphs and industrial conditions; and apply the ideas to unfamiliar reactions.
Biological catalysts
Enzymes are biological catalysts, generally proteins, that accelerate reactions in living systems and industrial biotechnology. Each enzyme has an active site suited to particular reactants, giving specificity.
Temperature and activity
Increasing temperature raises rate until an optimum is reached. Above the optimum, the enzyme structure changes and the active site loses its effective shape. The enzyme becomes denatured and activity falls sharply.
pH and specificity
Each enzyme has an optimum pH range. Extreme pH can alter protein structure and reduce activity. An enzyme does not shift chemical equilibrium; it increases the rates of both directions where both are catalysed.
Comparison with inorganic catalysts
Both enzymes and inorganic catalysts lower activation energy and remain chemically unchanged overall. Enzymes often work under mild conditions and are highly specific, but they can be more sensitive to temperature and pH.
Practical or data skill
Analyse enzyme-rate graphs against temperature or pH and identify the optimum, controlled variables and evidence of denaturation.
Examination tip
When enzymes are mentioned in a rate question, still use collision theory and activation energy where appropriate.
Review questions and suggested answers
Question 1
Why are enzymes specific?
Suggested answer
Their active sites are complementary to particular reactant molecules.
Question 2
What is denaturation?
Suggested answer
A change in enzyme structure that alters the active site and reduces activity.
Question 3
What feature is shared with inorganic catalysts?
Suggested answer
They lower activation energy and are unchanged overall.
