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5. (a) Sulfur dioxide combines with oxygen to form sulfur trioxide, in an exothermic reaction - Edexcel - GCSE Chemistry - Question 5 - 2017 - Paper 1
Question 5
5. (a) Sulfur dioxide combines with oxygen to form sulfur trioxide, in an exothermic reaction. $$2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g)$$ The reaction can r... show full transcript
Worked Solution & Example Answer:5. (a) Sulfur dioxide combines with oxygen to form sulfur trioxide, in an exothermic reaction - Edexcel - GCSE Chemistry - Question 5 - 2017 - Paper 1
Step 1
Explain why the equilibrium yield of sulfur trioxide decreases.
Answer
When the temperature is increased beyond 450°C for the exothermic reaction, Le Chatelier's principle states that the system will respond by shifting the equilibrium position to counteract the change imposed on it. In this case, the increase in temperature favors the endothermic reaction, which is the reverse reaction leading to the formation of sulfur dioxide and oxygen. As a result, the concentration of sulfur trioxide decreases, leading to a reduced equilibrium yield.
Step 2
Describe how the apparatus below can be used to obtain these results, showing how the results can be used to find the volume occupied by one mole of hydrogen gas, H_2, at room temperature and pressure.
Answer
To measure the volume of hydrogen gas produced, set up the apparatus as shown. The magnesium ribbon is placed in excess dilute sulfuric acid inside a conical flask. As the magnesium reacts with sulfuric acid, hydrogen gas is liberated. The gas travels through the delivery tube and is collected over water in the graduated gas jar or burette.
Measure the volume of hydrogen gas collected, which is 48 cm³ in this case. To determine the volume occupied by one mole of hydrogen gas at room temperature and pressure, use the molar volume at RTP, which is approximately 24 dm³ (24000 cm³).
Now, calculate the moles of magnesium used:
Using stoichiometry from the balanced equation, 1 mole of Mg produces 1 mole of H_2, hence the volume of 1 mole of H_2 can be calculated using the proportion of the collected gas:
If 0.00197 moles corresponds to 48 cm³, then for 1 mole it corresponds to:
Thus, we can conclude that one mole of hydrogen gas occupies approximately 24316 cm³ at room temperature and pressure.