Date | November 2019 | Marks available | 2 | Reference code | 19N.3.sl.TZ0.3 |
Level | SL | Paper | 3 | Time zone | TZ0 |
Command term | Explain | Question number | 3 | Adapted from | N/A |
Question
Catalysts are commonly used in industry.
Describe how a heterogeneous catalyst provides an alternative pathway for a reaction.
Distinguish between heterogeneous and homogeneous catalysts, giving one difference.
Nanotubes are used to support the active material in nanocatalysts.
Explain why oxygen cannot be used for the chemical vapour deposition (CVD) preparation of carbon nanotubes.
Markscheme
reactant(s) adsorb onto active sites/surface ✔
NOTE: Do not accept “absorb” for “adsorb” for M1.
Accept “bonds to” for “adsorb” for M1.
«reactant» bonds weakens «and products are desorbed» ✔
NOTE: Accept “bonds break/stretch «and products are desorbed»” for M2.
Award [1 max] for “lowers activation energy”.
Any one of the following:
NOTE: Accept “heterogeneous adsorb reactants and homogeneous” but do not accept “absorb” for “adsorb”.
Accept “heterogeneous have active sites and homogeneous do not”.
high temperature used ✔
oxygen/O2 reacts with carbon/C
OR
carbon dioxide/CO2 can form ✔