O-LevelChemistryRates of Reaction5070/21 · Oct/Nov 2022 · Q610 Marks

This question is about compounds of nitrogen.

(a)(i)The equation represents the equilibrium between N2O4 and NO2 at a high temperature in a closed container. N2O4(g) ⇌ 2NO2(g) Predict what happens to the position of equilibrium when the pressure is decreased. Explain your answer. prediction explanation[2]
(a)(ii)The table shows the concentration of NO2 in the closed container at three different temperatures. temperature in °C | concentration of NO2 in mol/dm³ ---|--- 100 | 0.04 150 | 0.40 200 | 4.00 State what this information shows about the enthalpy change of the forward reaction. Explain your answer. enthalpy change explanation[2]
(b)(i)Nitrogen dioxide, NO2, is made by heating lead(II) nitrate, Pb(NO3)2. The other products are lead(II) oxide and a gas which relights a glowing splint. Construct the equation for this reaction.[2]
(b)(ii)Nitrogen dioxide contributes to acid rain. State one effect of acid rain on organisms.[1]
(c)(i)Nitric acid, HNO3, is a strong acid. State the meaning of the term strong in strong acid.[1]
(c)(ii)Suggest a pH value for a concentrated solution of a strong acid.[1]
(c)(iii)Complete the ionic equation for the reaction of an acid with an alkali. H+ + ........ → H2O[1]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2022). The mark or mark type is shown in brackets.

[2] position of equilibrium moves to the right (1)
[2] fewer moles of gas on left of the equation / lower volume of gas on left of the equation (1)
[2] the reaction is endothermic (1)
[2] because there is a higher concentration of (NO2) at higher temperatures / there is a lower concentration of N2O4 at lower temperatures (1)
[2] 2Pb(NO3)2 → 2PbO + 4NO2 + O2 (2)
[2] correct formulae (1)
[2] correct balance (1)
[1] damage to tree leaves (in conifers) / kills organisms in lakes
[1] dissociates completely (in solution) / ionises completely (in solution)
[1] any value from 0 to 2 (inclusive of these values)
[1] OH-

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