(i) measure the change in pressure per unit time at constant volume «2 mol of gas become 3 mol»

OR

measure the change in volume per unit time at constant pressure ✔

(ii) the molecules may collide with an unsuitable orientation ✔

the collision energy may be less than the activation energy ✔

(iii) second curve starting at the origin with a lower maximum displaced to higher energy, staying above the axis at high energy «area under both curves the same» ✔

(iv) $E_\mathrm{a}$ marked as a vertical line on the energy axis ✔

at the higher temperature a greater proportion of molecules have energy equal to or greater than $E_\mathrm{a}$ «larger area under the curve to the right of $E_\mathrm{a}$», so a greater fraction of collisions are successful ✔

(v) the solid is chemically unchanged / its mass is unchanged at the end of the reaction ✔

the rate of reaction is greater in its presence «under otherwise identical conditions» ✔

(i) [1] a physical change that follows the increase in the amount of gas; do not accept pH measurement or titration. (ii) [2] M1 orientation; M2 energy below Ea. (iii) [1] no mark if the curve does not start at the origin, crosses the axis or has a larger area. (iv) [2] M1 Ea indicated; M2 greater proportion of molecules with E ≥ Ea. (v) [2] M1 unchanged at the end; M2 rate increased. Answers that only quote the definition of a catalyst without an observation do not score.