4 marksHigher
A catalyst changes the highest point of a reaction profile from 170 kJ to 115 kJ. Reactants remain at 40 kJ and products at 15 kJ.
.1Calculate the catalysed activation energy.
[2 marks] .2Evaluate the statement: "The catalyst releases an extra 55 kJ, so the reaction becomes more exothermic."
[2 marks] 4 marksFoundation and Higher
A polymer model contains 150 chains. Each chain contains 400 repeat units.
.1Calculate the total number of repeat units represented.
[2 marks] .2Explain why this model represents a polymer rather than a giant covalent lattice.
[2 marks] 4 marksHigher
A pupil estimates the energy change for
CH4+Cl2→CH3Cl+HCl. Bond energies are C-H 413, Cl-Cl 243, C-Cl 338 and H-Cl 431 kJ/mol.
.1Calculate the energy change using only bonds that change.
[3 marks] .2Evaluate the claim that breaking the C-H bond supplies the energy released.
[1 mark] 6 marksHigher
Two separate samples each have mass 8.0 g. One is oxygen gas,
O2, and the other is sulfur dioxide,
SO2. Ar: O = 16, S = 32.
.1Calculate the amount of oxygen molecules in the oxygen sample.
[2 marks] .2Calculate the amount of sulfur dioxide molecules in its sample.
[2 marks] .3Explain which sample contains more molecules and by what factor.
[2 marks] 5 marksFoundation and Higher
A filter designer chooses a single graphene sheet rather than a thick graphite block. Graphene consists of one layer of carbon atoms.
.1Compare the structures and explain two resulting properties of graphene.
[3 marks] .2Explain why evidence for strength alone cannot establish that graphene is a suitable filter.
[2 marks] 