QUESTION 25 (5 marks)
This graph depicts the changes in concentration over time for a nitrogen dioxide / dinitrogen tetroxide gaseous equilibrium in a closed system at constant temperature.
ibrium in a closed system at constant temperature
n a it ro ge n d iox ide / din itr oge changes
a) Determine the balanced chemical equation for the reaction in this system.
[1 mark]
b) Identify the time at which equilibrium is reached.
[1 mark]
c) If temperature is held constant, predict the effect that doubling the volume at 100 seconds would have on the closed system by sketching the change that would occur and the approximate position of the new equilibrium on the graph.
[3 marks]
Note: If you make a mistake, draw a line through this graph and use the additional graph provided on page 13 of this question and response book.
QCAA guide · typeset solution
QCAA sample response and mark allocation
25 | a) | N2O4(g) ⇌ 2NO2(g) | • provides N2O4(g) ⇌ 2NO2(g) [1 mark] | |
b) | 80 seconds | • identifies time as 80 [1 mark] | Accept values between 70 and 90 inclusive. |
c) | • indicates that at 100 s concentration of N2O4 and NO2 would halve [1 mark] • indicates that after 100 s concentration of N2O4 would decrease to a new equilibrium at a lower concentration [1 mark] • indicates that after 100 s concentration of NO2 would increase to a new equilibrium at a higher concentration [1 mark] |
QCAA sample response and marking criteria reproduced from the official guide.
Compare your working with the guide above.