Catalysis

    OCR
    GCSE

    Catalysts increase the rate of chemical reactions without undergoing permanent chemical change. They function by providing an alternative reaction pathway characterized by a lower activation energy than the uncatalyzed route. This mechanism increases the proportion of particles possessing sufficient energy to react upon collision. Mastery requires interpreting reaction profiles to compare catalyzed and uncatalyzed pathways and evaluating the economic and environmental benefits of catalysts in industrial processes.

    0
    Objectives
    4
    Exam Tips
    4
    Pitfalls
    4
    Key Terms
    5
    Mark Points

    What You Need to Demonstrate

    Key skills and knowledge for this topic

    • Award 1 mark for stating a catalyst increases the rate of reaction while remaining chemically unchanged at the end
    • Credit responses that explicitly state the catalyst provides an 'alternative reaction pathway'
    • Award 1 mark for linking the alternative pathway to a 'lower activation energy'
    • In reaction profiles, award marks for drawing the catalysed curve starting and ending at the exact same energy levels as the uncatalysed reaction
    • For enzymes, credit references to the 'lock and key' mechanism or the active site specificity

    Example Examiner Feedback

    Real feedback patterns examiners use when marking

    • "You correctly defined the catalyst, but you must also mention the 'alternative pathway' to secure the second mark"
    • "Your reaction profile is good, but check your activation energy arrow—it must start from the reactant line, not the bottom axis"
    • "Be careful not to confuse rate with yield; the catalyst speeds up the process but does not produce more product"
    • "Excellent use of the term 'activation energy'—now try to apply this to why transition metals are often used as catalysts"

    Marking Points

    Key points examiners look for in your answers

    • Award 1 mark for stating a catalyst increases the rate of reaction while remaining chemically unchanged at the end
    • Credit responses that explicitly state the catalyst provides an 'alternative reaction pathway'
    • Award 1 mark for linking the alternative pathway to a 'lower activation energy'
    • In reaction profiles, award marks for drawing the catalysed curve starting and ending at the exact same energy levels as the uncatalysed reaction
    • For enzymes, credit references to the 'lock and key' mechanism or the active site specificity

    Examiner Tips

    Expert advice for maximising your marks

    • 💡Memorize the phrase 'alternative reaction pathway with lower activation energy'—it is a standard 2-mark requirement on Higher Tier papers
    • 💡When drawing energy profiles, ensure the 'hump' for the catalysed reaction is lower than the uncatalysed one, but the overall energy change (Delta H) remains identical
    • 💡If asked to evaluate a catalyst in an industrial context, consider economic factors (cost of catalyst vs. energy savings) and environmental impact
    • 💡Distinguish between 'mass unchanged' and 'chemically unchanged'—both are true, but the latter is the standard chemical definition required

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Stating that catalysts 'do not take part' in the reaction; examiners expect the understanding that they participate but are regenerated
    • Drawing the activation energy arrow starting from the x-axis (zero energy) instead of the reactant energy level line
    • Suggesting catalysts increase the yield of a reaction; they only reduce the time taken to reach equilibrium
    • Confusing the effect of temperature on enzymes (denaturation) with the effect on inorganic catalysts

    Key Terminology

    Essential terms to know

    Activation energy reduction
    Alternative reaction pathways
    Reaction profiles and energy diagrams
    Industrial and environmental sustainability

    Likely Command Words

    How questions on this topic are typically asked

    Define
    Explain
    Draw
    Compare
    Evaluate
    Describe

    Practical Links

    Related required practicals

    • •{"code":"PAG C5","title":"Investigation of the rate of reaction","relevance":"Decomposition of hydrogen peroxide using manganese(IV) oxide, liver, or potato as catalysts"}

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