Photo AI
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
Step 1
Step 2
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 a few drops of a high concentration of thiocyanate ions are added to the orange equilibrium mixture, the solution becomes more red. This occurs because the position of equilibrium shifts to the right, increasing the concentration of Fe(SCN)²⁺ ions as the forward reaction is favored, resulting in a deeper red color.
Step 3
3. A water bath is set up at a temperature above room temperature. When a test tube containing the orange equilibrium mixture is placed in the water bath, the mixture becomes more yellow. Explain what this shows about the energy change for the forward reaction.
Answer
The change to a more yellow color indicates that the equilibrium position shifts to the left when heated. This shows that the forward reaction is exothermic, meaning it releases heat; thus, as temperature increases, the reverse reaction is favored to counteract the temperature rise.
Step 4
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 gases present in this reaction. The equilibrium is established in a solution, where pressure changes do not influence the concentration of the solutes involved.
Step 5