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The equilibrium equation for the reaction of iodine with hydrogen cyanide in aqueous solution is given - HSC - SSCE Chemistry - Question 26 - 2024 - Paper 1
Question 26
The equilibrium equation for the reaction of iodine with hydrogen cyanide in aqueous solution is given. I2(aq) + HCN(aq) ⇌ ICN(aq) + H+(aq) At t = 0 min, I2 was ad... show full transcript
Worked Solution & Example Answer:The equilibrium equation for the reaction of iodine with hydrogen cyanide in aqueous solution is given - HSC - SSCE Chemistry - Question 26 - 2024 - Paper 1
Step 1
a) On the axes provided, sketch a graph to show how [I2] changes in the solution between t = 0 min and t = 6 min.
Answer
To sketch the graph of [I2] over time:
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Identify the initial concentration: At t = 0 min, [I2] is at its maximum, which is 2.0 x 10−5 mol L−1.
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Reacting species: Given that half of I2 reacted after 3 minutes, this indicates that the concentration of I2 will decrease over this time.
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Graphing the concentration:
- From time 0 to 3 min, the concentration will decrease sharply as I2 is consumed.
- From 3 to 6 min, the decrease will level off as equilibrium is approached.
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Axes labeling: Make sure to label the axes correctly, with [I2] on the y-axis and time (in minutes) on the x-axis. The graph should start at 2.0 x 10−5 mol L−1, drop significantly by the 3-minute mark, and then stabilize towards the end.
The graph should reflect a decaying curve that starts at the peak and levels out as time progresses.
Step 2
b) Using collision theory, explain the rate of reaction between t = 0 min and t = 6 min.
Answer
To explain the rate of reaction using collision theory:
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Initial conditions: At t = 0, the [I2] is at its highest concentration, resulting in more frequent and successful collisions between reactant molecules which increases the rate of the forward reaction.
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Reaction progress: As time progresses, [I2] decreases since it is being consumed in the reaction, leading to fewer collisions. Consequently, the rate of the reaction slows down as the concentration of I2 diminishes.
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Equilibrium state: After 3 minutes, the system reaches equilibrium, where the rate of the forward reaction equals the rate of the reverse reaction. At this point, even though [I2] is at a lower concentration, the overall rates become constant as established by the principle of dynamic equilibrium.
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Conclusion: Therefore, from t = 0 min to t = 6 min, the initial high concentration of [I2] results in a high rate of forward reaction which gradually decreases as the concentration of [I2] reduces.