Comment: Look for the indicative marking points first, then consider the mark for the structure of the answer and sustained line of reasoning.
Indicative content
3 or 4 indicative points would get 1 mark for reasoning, and 0, 1 or 2 indicative points would score zero marks for reasoning.
If there is any incorrect chemistry, deduct mark(s) from the reasoning. If no reasoning mark(s) awarded do not deduct mark(s). e.g. iron catalysing formation of ammonia from nitrogen and hydrogen but naming it the Contact Process / incorrect formula e.g. for persulfate ions
Allow correct formulae for names
Do not award examples that are not transition metals, ions or compounds
- IP1 Comparison - Activation energy
both catalysts increase the rate of reaction by providing an alternative route / mechanism with a lower activation energy
- IP2 Phase
a heterogeneous catalyst is in a different phase from the reactants and a homogeneous catalyst is in the same phase as the reactants / all solutions / gases
- IP3 Example of heterogeneous
example of a heterogeneous catalyst and reaction it catalyses e.g. iron and Haber Process, nickel and hydrogenation of alkenes, platinum in a catalytic converter / with CO and NO
- IP4 Example of homogeneous example of a homogeneous catalyst and reaction it catalyses e.g. iron(II) / iron(III) ions and reaction between iodide ions and persulfate ions
- IP5 Mechanism of heterogeneous reactant molecules are adsorbed onto the catalyst surface, the bonds are weakened, reaction takes place then the product molecules are desorbed
Allow this shown on a Maxwell-Boltzmann distribution / reaction profile diagram
Allow (physical) state for phase Allow heterogeneous catalysts are easy to separate from the reaction mixture / reactants / products and homogeneous catalysts are difficult to separate from the reaction mixture / reactants / products
