How many QCAA Chemistry questions cover Chemical equilibrium systems?

AusGrader has 325 QCAA Chemistry questions on Chemical equilibrium systems, all with instant AI grading and detailed marking feedback.

QCAA (QCE) Chemistry — Chemical equilibrium systems Questions & Answers | AusGrader

Q1

2024

QCAA

Paper 1

1 mark

Q1

1 mark

The question refer sto hydrated copper sulfate and its decomposition when heated.

Hydrated copper sulfate ( $CuSO_4\cdot H_2O$ ) decomposes to form copper sulfate (CuSO $_4$ ) and water when heated.

$\text{heat} + \text{CuSO}_4\cdot\text{H}_2\text{O(s)} \rightleftharpoons \text{CuSO}_4\text{(s)} + \text{H}_2\text{O(g)}$

Which of the following is exchanged with the surrounding environment when CuSO $_4$ xH $_2$ O(s) is heated in a closed system to establish dynamic equilibrium?

A

heat

B

H $_2$ O(g)

C

CuSO $_4$ (s) + H $_2$ O(g)

D

heat + CuSO $_4$ xH $_2$ O(s)

Q1

2021

QCAA

Paper 1

1 mark

Q1

1 mark

Melting is a

A

physical change that is reversible.

B

chemical change that is reversible.

C

physical change that is irreversible.

D

chemical change that is irreversible.

Q21

2024

QCAA

Paper 1

3 marks

Q21

Reactants A and B are placed in a 1.00 L container and react to form product C. The reaction then reaches equilibrium.

$\text{A(g)} + \text{B(g)} \rightleftharpoons \text{C(g)} \quad (K_c = 9.9 \times 10^2)$

Q21a

1 mark

Explain why a reversible arrow ( $\rightleftharpoons$ ) is used to symbolise this reaction.

The reversible arrow indicates that the reaction occurs in both directions (forward and reverse) simultaneously.

Marking Criteria

Descriptor	Marks
Explains that forward and reverse reactions occur simultaneously	1

Q21b

2 marks

Deduce whether the equilibrium for the reaction lies towards the reactants or products. Explain your reasoning.

$K_c$ is greater than 1, therefore the equilibrium for the reaction lies towards the products.

Marking Criteria

Descriptor	Marks
Deduces the equilibrium lies towards the products	1
Explains that $K_c$ is greater than 1	1

Q3

2024

QCAA

Paper 2

9 marks

Q3

The concentration, pH and dissociation constant ( $K_a$ ) of aqueous solutions of ethanoic acid and two unknown monoprotic acids, I and II, are shown.

Acid	Concentration (M)	pH	$K_a$
CH $_3$ COOH(aq)	0.2		$1.8 \times 10^{-5}$
I	0.2	1.9	$6.6 \times 10^{-4}$
II	0.1	1.1	$1.3 \times 10^6$

Q3a

3 marks

Compare the relative strength of an aqueous solution of acid I and CH $_3$ COOH(aq).

Similarity: both weak acids

Difference: ethanoic acid ( $CH_3COOH$ ) is weaker than acid I

Significance: Ethanoic acid dissociates less to produce a lower $[H^+]$

Marking Criteria

Descriptor	Marks
Identifies that both acids are weak acids	1
Identifies that ethanoic acid is weaker than acid I	1
Explains that ethanoic acid dissociates less to produce a lower [H⁺]	1

Q3b

3 marks

Determine whether an aqueous solution of acid I or acid II would have a higher electrical conductivity. Explain your reasoning.

Acid II has a $K_a$ greater than 1 and is therefore a strong acid, while acid I is a weak acid due to small $K_a$ . Acid II dissociates to produce more ions in an aqueous solution than acid I.
Therefore, acid II has a higher electrical conductivity than acid I.

Marking Criteria

Descriptor	Marks
Identifies that acid II is stronger than acid I	1
Explains that acid II dissociates to produce more ions in solution	1
Determines that the electrical conductivity of acid II will be greater than acid I	1

Q3c

3 marks

Calculate the pH of 0.2 M CH $_3$ COOH(aq). Show your working.

$[H_3O^+] = [CH_3COO^-] = x$

$[CH_3COOH] = \frac{[H_3O^+][CH_3COO^-]}{K_a}$

$0.2 = \frac{(x)^2}{1.8\times10^{-5}}$

$[H_3O^+] = 1.9 \times 10^{-3} \text{ M}$

$pH = -\log_{10}[H_3O^+]$

$pH = 3$

Marking Criteria

Descriptor	Marks
Identifies $[H_3O^+] = [CH_3COO^-]$	1
Determines $[H_3O^+]$	1
Calculates pH	1

Q7

2023

QCAA

Paper 2

4 marks

Q7

When heated in a sealed container, solid mercury(II) oxide (HgO) decomposed to form metallic mercury (Hg) and oxygen gas (O $_2$ ).

$2\text{HgO(s)} \rightleftharpoons 2\text{Hg(l)} + \text{O}_2\text{(g)}$
Orange $\quad$ Silver $\quad$ Colourless

Q7a

1 mark

Identify whether the reaction occurs in an open or closed system.

Descriptor	Marks
identifies closed system	1

Q7b

3 marks

Explain why the colour of the system does not change once equilibrium is established.

At equilibrium there is no net change in the concentration of the reactants and the products.
The forward and reverse reactions are still occurring.
As the forward reaction is equal to the rate of the reverse reaction the colour of the system at equilibrium remains constant.

Marking Criteria

Descriptor	Marks
identifies the concentration of the reactants and products remain constant at equilibrium	1
explains that the forward and reverse reactions are occurring simultaneously	1
explains forward reaction is equal to reverse reaction and therefore there is no colour change	1

QCAA Chemistry Chemical equilibrium systems

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