Define the term chemical equilibrium - NSC Physical Sciences - Question 6 - 2021 - Paper 2
Question 6
Define the term chemical equilibrium.
The stage in a chemical reaction when the rate of forward reaction equals the rate of reverse reaction.
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Worked Solution & Example Answer:Define the term chemical equilibrium - NSC Physical Sciences - Question 6 - 2021 - Paper 2
Step 1
Define the term chemical equilibrium.
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Answer
Chemical equilibrium is defined as the stage in a chemical reaction where the rate of the forward reaction is equal to the rate of the reverse reaction, resulting in constant concentrations of reactants and products.
Step 2
Which ONE of the curves, X or Y, represents the changes in the concentration of the products? Give a reason for the answer.
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Answer
Curve Y represents the changes in the concentration of the products. This is because, as the reaction proceeds, the concentration of products increases while that of reactants decreases.
Step 3
How does the rate of the forward reaction compare to that of the reverse reaction at t = 4 minutes? Choose from HIGHER THAN, LOWER THAN OR EQUAL TO.
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Answer
At t = 4 minutes, the rate of the forward reaction is LOWER THAN the rate of the reverse reaction, as indicated by the concentration changes in the graph.
Step 4
Calculate the number of moles of iodine, I2(g), present at time t = 6 minutes.
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Answer
Given that Kc = 0.04, we know that:
Kc=[H2]2[H2]2[I2]
At t = 6 minutes, let 'x' be the change in concentration for I2.
Substituting:
Initial moles H2 = 0.5 mol, so [H2] at equilibrium = 0.5 - 2x
At equilibrium, Kc expression becomes:
0.04=(0.5−2x)2(2x)2
Solving the equilibrium concentrations gives x = 0.071 mol. Thus, the moles of I2 is:
n(I2)=0.071×0.5=0.036mol
Step 5
Which reaction(s) show(s) an increase in rate at t = 10 minutes? Choose from FORWARD, REVERSE OR BOTH FORWARD AND REVERSE.
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Answer
At t = 10 minutes, both forward and reverse reactions show an increase in rate due to the increase in temperature.
Step 6
Is the heat of reaction (ΔH) for this reaction POSITIVE or NEGATIVE? Fully explain the answer.
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Answer
The heat of reaction (ΔH) is POSITIVE because increasing the temperature favors the endothermic direction of the reaction, suggesting that the reaction absorbs heat.
