Oxford Revise AQA GCSE Chemistry | Chapter C13 answers

C13: Equilibrium

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AO / Specification reference

01.1

92 kJ

allow ‘–92 kJ’

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AO2

4.6.2.2

01.2

if a system is an equilibrium and a change is made to any of the conditions, the system responds to counteract the change

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AO1

4.6.2.4

01.3

it shifts to the right

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AO2

4.6.2.7

02.1

one O atom should have 6 dots and 2 crosses and other should have 6 crosses and 2 dots.

the O atoms should be sharing 2 dots and 2 crosses

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AO2

4.2.1.4

02.2

a reaction that transfers energy to the surroundings

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AO1

4.5.1.1

02.3

more SO3 is added – shifts to the left

pressure is increased – shifts to the right

temperature is increased – shifts to the left

more O2 is added – shifts to the right

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AO2

4.6.2.5

4.6.2.6

4.6.2.7

03.1

methanol gas is the product

in unsealed container, product would escape (into surroundings)

therefore, forward reaction would continue (to produce methanol) or continue to completion

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AO1

4.6.2.3

03.2

Level 3: Three conditions identified with matching description of how the change will affect the position of the equilibrium. Full explanation of why change occurs provided.

5-6

AO1

4.6.2.4

4.6.2.5

4.6.2.6

4.6.2.7

Level 2: At least two conditions identified with a matching description of how the change will affect the position of the equilibrium. Attempt at explanations given, with some accurate points given.

3-4

Level 1: At least one condition identified, thought description of how the change will affect position not given, incorrect, or incomplete. No attempt at explanation provided.

1-2

No relevant content

0

Indicative content

increasing total pressure:

  • shifts the equilibrium to the right/results in a greater relative amount of product
  • because there is a smaller number of molecules on this side of the equation

decreasing temperature:

  • shifts the equilibrium to the right/results in a greater relative amount of product
  • because the reaction is exothermic in the reaction shown

increasing the amount/concentration of the reactant:

  • shifts equilibrium to the right/results in a greater relative amount of product until equilibrium is established again
  • because there is a smaller number of molecules shown in the equation on the left and the concentrations of all substances will change until equilibrium is reached again

03.3

mass of one mole of CO = 12 + 16 = 28g

\(
10{\rm{\ g\ of\ CO\ is\ }}\frac{{10}}{{28}} = 0.3571{\rm{\ mol}}
\)

from the equation, 0.3571 moles of CO makes 0.3571 moles of methanol

mass of one mole of methanol = 12 + 16 + (4 × 1) = 32 g

mass of 0.3571 mol of methanol = 0.3571 × 32 = 11.4272

= 11.4 g to three significant figures

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AO2

4.3.2.1

4.3.2.2

04.1

reversible

accept ‘equilibrium’

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AO1

4.6.2.1

04.2

H2 and I2 react together to make HI at the same rate that HI reacts to form H2 and I2

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AO2

4.6.2.3

04.3

when H2 and I2 react to form HI

energy is transferred from the surroundings/the system takes in energy from the surroundings

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AO1

4.5.1.1

4.6.2.1

05.1

reactants and products can escape from the apparatus

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AO2

4.6.2.3

05.2

Bunsen burner

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AO1

05.3

steam/water/water vapour

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AO2

4.6.2.2

05.4

attach bung to test tube

attach delivery tube to test tube

feed delivery tube into beaker in ice water

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AO3

06.1

place it in a bigger water bath/ensure that the level of the solution is below the level of the water or stir it

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AO3

06.2

heating the mixture shifts the equilibrium towards the blue cobalt ion solution or right hand side or product side

so the reaction is endothermic in the forward direction (from left to right)

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AO3

4.6.2.6

06.3

pink to blue

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AO3

4.6.2.5

06.4

concentration of chloride ions is increased

so a change occurs to counteract the change

and the equilibrium shifts to the right/relative amount of product increases

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AO2

4.6.2.5

07.1

increases the pressure

so more of the colourless N2O4 is formed

because the system is responding to counteract the change

by shifting the position of the equilibrium to the side with the smaller number of molecules

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AO3

4.6.2.4

4.6.2.7

07.2

the temperature of the mixture is decreased

so the relative amount of product at equilibrium decreases or position of equilibrium moves to the left

so the colour change gets lighter/colourless/clear

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AO2

4.6.2.6

07.3

no effect

because there are the same number of molecules shown in the equation in both the products and reactants

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AO2

4.6.2.7

08.1

three (minutes)

the amounts of both X and Y are constant from this time onwards

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AO3

08.2

they are the same

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AO1

4.6.2.3

08.3

forward

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AO3

4.6.2.2

09.1

ICl(l) + Cl2(g) ⇌ ICl3(s)

or

ICl3(s) ⇌ Cl2 (g) + ICl(l)

one mark for identifying ICl and Cl2 as the reactants

one mark for state symbols

one mark for reversible arrow

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AO3

4.6.2.1

09.2

exothermic

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AO2

4.6.2.2

09.3

ice bath reduces the temperature of the system

in exothermic reaction, energy is transferred to the surroundings

so increasing the temperature/minimising the change

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AO3

4.6.2.6

10.1

ammonium chloride

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AO3

4.6.2.1

10.2

reaction is reversible

therefore, as ammonia and hydrogen chloride gases cool

they react to form ammonium chloride

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AO2

4.6.2.1

10.3

crystals turn blue

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AO3

4.6.2.1

10.4

test tube would warm up

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AO3

4.6.2.2

11.1

three

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AO2

4.3.2.1

11.2

14 + (3 × 1)

= 17

award two marks for correct answer with no working

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AO2

4.3.1.2

11.3

\(
\begin{array}{l}
\frac{{{\rm{68}}}}{{{\rm{17}}}}\\
= 4
\end{array}
\)

award two marks for correct answer with no working

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AO2

4.3.2.1

11.4

4 × 6.02 × 1023

= 2.408 × 1024

= 2.41 × 1024

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AO2

4.3.2.1

12.1

two from:

  • moves around on surface of water
  • fizzing
  • lilac/mauve/purple flame
  • if universal indicator has been added to the water, these is a colour change from green to purple/blue

one for each correct observation

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AO1

4.1.2.5

12.2

lithium hydroxide

hydrogen

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AO1

4.1.2.5

4.4.1.2

12.3

no change

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AO1

4.4.1.2

13.1

use a pipette to transfer the sodium hydroxide

because its resolution is higher/it measures more accurately

add a few drops of indicator only

so it is easier to detect the colour change/to avoid wasting indicator

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AO3

4.4.2.3

13.2

repeat without indicator

so that the crystals are not contaminated with indicator

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AO3

4.4.2.3

13.3

0.025 mol of sodium hydroxide makes 0.025 mol of sodium chloride

molar mass of sodium chloride is 23 + 35.5 = 58.5

mass of 0.025 mol = 0.025 × 58.5 = 1.4625

= 1.5 (g) to two significant figures

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AO2

4.3.2.1

4.3.2.2

14.1

2SO2

g

two

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AO2

14.2

forward reaction

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AO2

4.6.2.2

14.3

more energy transferred to break reactant bonds than is transferred to surroundings on formation of product bonds

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AO3

4.5.1.3

14.4

decrease yield

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AO2

4.6.2.6

14.5

high/increase yield

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AO1

4.6.1.2

14.6

provides an alternative reaction pathway

with a lower activation energy

so more frequent collisions with enough energy to react

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AO1

4.6.1.4

14.7

increase pressure

fewer molecules in the products

so equilibrium position will shift right to minimise change

accept answer that matches with student’s balanced equation

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AO1

4.6.2.7

14.8

expensive/dangerous

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AO3

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