Zadanie 2a

(i) Change of state: sublimation ✔

Type of force: London / dispersion forces ✔

(ii) the change from I₂(s) to I₂(g) is endothermic «absorbs energy» ✔

the equilibrium shifts to the right / more vapour is formed «so the colour is deeper» ✔

(iii) Any two of:

more gas molecules / moles of gas in the flask OR the concentration of the gas increases ✔

the molecules have greater «average» kinetic energy OR the molecules move faster ✔

the molecules collide with the walls of the flask with greater force ✔

the molecules collide with the walls more frequently ✔

(iv) V = 2.50 × 10⁻⁴ m³ AND T = 308 K ✔

«$n = \dfrac{m}{M} = \dfrac{3.05 \times 10^{-3}}{2 \times 126.90} =$» 1.20 × 10⁻⁵ «mol» ✔

«$P = \dfrac{nRT}{V} = \dfrac{1.20 \times 10^{-5} \times 8.31 \times 308}{2.50 \times 10^{-4}} =$» 123 «Pa» / 0.123 «kPa» ✔

(i) [2] M1 sublimation; M2 London / dispersion forces; do not accept van der Waals forces or intermolecular forces for M2. (ii) [2] M1 endothermic change; M2 equilibrium shifts to the vapour side. (iii) [2 max] one mark for each of two different reasons from the key. (iv) [3] M1 volume in m³ AND temperature in K; M2 amount of iodine, using the molar mass of I₂; M3 pressure. Award [3] for a correct final answer; ECF from M1 and M2.