Lithium reacts with nitrogen at room temperature to form solid $$$\mathrm{Li}_{3} \mathrm{~N}$$$. Three vessels of equal volume are connected by taps 1 and 2 as shown. At the start, taps 1 and 2 are closed, the left-hand vessel is evacuated, the middle vessel has the indicated reaction at equilibrium and the right-hand vessel contains lithium only. Which action would allow the equilibrium mixture to contain the most ammonia?

Keep both taps 1 and 2 closed.

Open both taps 1 and 2.

Open tap 1 only.

Open tap 2 only.

Chemistry

IGCSE&ALevel

CAIE

Exam No：9701_w24_qp_11 Year：2024 Question No：12

Answer:

Knowledge points:

7.1.1.1 understand what is meant by a reversible reaction

7.1.1.2 understand what is meant by dynamic equilibrium in terms of the rate of forward and reverse reactions being equal and the concentration of reactants and products remaining constant

7.1.1.3 understand the need for a closed system in order to establish dynamic equilibrium

7.1.10 describe and explain the conditions used in the Haber process and the Contact process, as examples of the importance of an understanding of dynamic equilibrium in the chemical industry and the application of Le Chatelier’s principle

7.1.2 define Le Chatelier’s principle as: if a change is made to a system at dynamic equilibrium, the position of equilibrium moves to minimise this change

7.1.3 use Le Chatelier’s principle to deduce qualitatively (from appropriate information) the effects of changes in temperature, concentration, pressure or presence of a catalyst on a system at equilibrium

7.1.4 deduce expressions for equilibrium constants in terms of concentrations,

7.1.5 use the terms mole fraction and partial pressure

7.1.6 deduce expressions for equilibrium constants in terms of partial pressures,

7.1.7 use the expressions to carry out calculations (such calculations will not require the solving of quadratic equations)

7.1.8 calculate the quantities present at equilibrium, given appropriate data

7.1.9 state whether changes in temperature, concentration or pressure or the presence of a catalyst affect the value of the equilibrium constant for a reaction

8.1.1 explain and use the term rate of reaction, frequency of collisions, effective collisions and non-effective collisions

8.1.2 explain qualitatively, in terms of frequency of effective collisions, the effect of concentration and pressure changes on the rate of a reaction

Answer:

Knowledge points:

Solution:

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