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This question is about a reversible reaction - AQA - GCSE Chemistry - Question 10 - 2020 - Paper 2
Question 10
This question is about a reversible reaction. The reaction between solutions of iron(III) ions (Fe³⁺) and thiocyanate ions (SCN⁻) is reversible. The ionic equation... show full transcript
Worked Solution & Example Answer:This question is about a reversible reaction - AQA - GCSE Chemistry - Question 10 - 2020 - Paper 2
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2. A few drops of a colourless solution containing a high concentration of thiocyanate ions (SCN⁻) are added to the orange equilibrium mixture. Explain the colour change observed.
Answer
When the colorless solution with high concentrations of thiocyanate ions is added to the orange equilibrium mixture, the mixture becomes more red.
This occurs because the position of equilibrium shifts to the right, increasing the concentration of iron(III) thiocyanate, FeSCN²⁺. This results in a more intense red color as the concentration of the red species increases, while the concentration of the yellow species decreases.
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3. A water bath is set up at a temperature above room temperature. Explain what this shows about the energy change for the forward reaction.
Answer
Placing the orange equilibrium mixture in a water bath at a higher temperature causes the mixture to become more yellow, indicating that the equilibrium position has shifted to the left.
This shift signifies that the forward reaction is exothermic; hence, as the temperature increases, the system counteracts this change by favoring the reverse reaction, which absorbs heat.
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4. Explain why a change in pressure does not affect the colour of the equilibrium mixture.
Answer
A change in pressure does not affect the colour of the equilibrium mixture because there are no gaseous reactants or products involved in the reaction. Since the reaction occurs entirely in aqueous solutions, pressure changes have no influence on the position of equilibrium, and thus, the colour remains unchanged.
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