An exothermic synthesis gives the following measured data. At 250 °C: equilibrium yield 80%, time to equilibrium 40 min. At 350 °C: yield 60%, time 8 min. A plant must reach equilibrium within 10 min and obtain at least 55% yield.
.1
Calculate the factor by which equilibration is quicker at 350 °C.
[2 marks]
.2
Justify a temperature choice from these two settings and explain why the highest yield alone is not the best criterion.
[2 marks]
4 marksFoundation and Higher
Spec and skills
Original practice question
Answer and supported method checks
A student says: "Crude oil is a compound. Fractional distillation breaks its molecules into simpler hydrocarbons. Each fraction contains one pure substance."
Evaluate each part of this explanation.
[4 marks]
4 marksFoundation and Higher
Spec and skills
Original practice question
Answer and supported method checks
A company claims that because its hydrocarbon fuel burns with no smoke it causes neither acid rain nor climate change. The fuel contains small amounts of sulfur and is burned at high temperature in air.
Evaluate the claim using the possible gaseous products.
[4 marks]
5 marksHigher
Spec and skills
Original practice question
Answer and supported method checks
A trial compares conventional mining with bioleaching for the same mass of copper recovered. Mining causes 120 units of landscape disturbance and uses 900 units of energy; bioleaching causes 35 and uses 600. Bioleaching takes much longer and its leachate must be contained.
.1
Calculate the percentage energy saving using bioleaching compared with mining.
[2 marks]
.2
Evaluate the claim that bioleaching has no environmental disadvantages.
[3 marks]
4 marksFoundation and Higher
Spec and skills
Original practice question
Answer and supported method checks
A reaction uses the same solution concentration at 20 °C and 35 °C. A student explains the faster reaction at 35 °C by saying particles are larger and the activation energy has decreased.
