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Sulfur has a low melting point compared to metals. Use its structure to explain this.
Solid sulfur consists of S₈ molecules held together by weak intermolecular forces, which require little energy to overcome.
A solid sulfur sample changes crystal shape at 96°C without changing chemical composition. What does this indicate?
A change in allotrope from rhombic sulfur to monoclinic sulfur.
Sulfur burns in oxygen producing a choking gas. Write the equation and state the oxidation state change of sulfur.
S + O₂ → SO₂; sulfur is oxidised from 0 to +4.
The conversion of SO₂ to SO₃ is reversible. Why is a catalyst essential in this step?
To increase the rate of reaction so equilibrium is reached faster.
Sulfur dioxide is released from power stations. State one chemical reason it causes environmental damage.
It forms acids when dissolved in rainwater.
Solid sulfur does not conduct electricity. Explain this using bonding and particle type.
Sulfur is made of neutral S₈ molecules with no mobile ions or delocalised electrons to carry charge.
Molten sulfur is cooled rapidly in cold water. Explain why the product is elastic rather than crystalline.
Rapid cooling prevents S₈ rings reforming, producing long-chain molecules that tangle.
Iron and sulfur are heated together. Explain why the product cannot be separated using a magnet.
A chemical compound (FeS) is formed, not a physical mixture.
Explain why SO₃ is not reacted directly with water in the Contact Process.
The reaction is extremely exothermic and produces acid mist that is difficult to control.
Explain how sulfur dioxide can reduce the pH of a lake far from its source.
SO₂ forms acid rain which is transported by wind before falling.
Explain why sulfur forms S²⁻ ions rather than S⁶⁺ ions in ionic compounds.
Gaining two electrons is energetically easier than losing six, allowing sulfur to achieve a stable noble gas configuration.
Plastic sulfur left at room temperature becomes brittle after several days. Explain why.
Plastic sulfur is unstable and slowly converts into the more stable rhombic sulfur.
Hydrogen sulfide is formed in a direct reaction. Explain why this gas is acidic in water.
H₂S dissolves to release hydrogen ions, forming an acidic solution.
Oleum is first formed before sulfuric acid. Explain the industrial advantage of this step.
It allows controlled dilution to safely produce concentrated sulfuric acid.
Concentrated sulfuric acid chars sugar in a demonstration. Explain why.
It removes water due to its strong dehydrating properties.
Explain why sulfur shows both ionic bonding with metals and covalent bonding with non-metals.
With metals, sulfur gains electrons to form S²⁻ ions; with non-metals, electrons are shared to complete outer shells.
Explain why rhombic sulfur is the most stable allotrope under normal conditions.
It has the lowest energy arrangement of sulfur atoms at room temperature.
Explain why sulfur dioxide is classified as an acidic oxide using an equation
SO₂ + H₂O → H₂SO₃; it forms an acid in water.
Explain why a temperature of about 450°C is chosen rather than a lower temperature.
Lower temperatures give higher yield but the reaction is too slow for industry.
Explain why sulfuric acid causes deeper burns than many other acids.
It is both corrosive and dehydrating, destroying tissue rapidly.
The reaction
2SO₂(g) + O₂(g) ⇌ 2SO₃(g) ΔH = –196 kJ mol⁻¹
is carried out at 450 °C and 2 atm.
Explain why a temperature of 450 °C is used instead of a lower temperature that would give a higher equilibrium yield.
Lower temperatures increase SO₃ yield (exothermic reaction)
BUT reaction rate becomes too slow
450 °C is a compromise between rate and yield
The reaction
2SO₂(g) + O₂(g) ⇌ 2SO₃(g) ΔH = –196 kJ mol⁻¹
is carried out at 450 °C and 2 atm.
Explain why increasing pressure above 2 atm is not economically favorable.
Increasing pressure shifts equilibrium right (fewer gas moles)
Yield increase is small
High pressure increases costs and safety risks
Therefore not economical
Direct addition of SO₃ to water is avoided in industry.
Explain why SO₃ is first reacted with concentrated H₂SO₄ to form oleum.
Reaction of SO₃ with water is violently exothermic
Produces acid mist
Difficult to control safely
Oleum allows controlled dilution
Direct addition of SO₃ to water is avoided in industry.
Write the equations for both steps.
SO₃ + H₂SO₄ → H₂S₂O₇
H₂S₂O₇ + H₂O → 2H₂SO₄
Sulfuric acid production is used as an indicator of industrial development. Explain why this is valid.
It is required in fertilizers, batteries, detergents, and chemical manufacture.