A petroleum refinery separates crude oil into fractions and then converts some fractions into higher-value products before shipping them to distributors. A simplified process flow is shown below.
1. Crude oil is heated to about 400 °C and introduced into a fractionating column; vapor rises, condenses at different heights, and is collected as separate liquid streams (e.g., gasoline, kerosene, diesel).
2. A portion of the gasoline fraction is blended with oxygenates (e.g., ethanol) to improve octane rating.
3. Tanker trucks deliver the blended fuel to filling stations, where it is pumped into automobile fuel tanks.
4. Inside an automobile engine, the blended fuel reacts with oxygen in a spark-ignition cylinder and the products exit the tailpipe.
Answer the following questions about steps 1-4.
(a) Identify each step (1–4) as involving a physical change, a chemical change, or both. For any step that involves both, briefly separate the sub-processes into physical and chemical portions.
(b) For each step, cite specific evidence available to plant engineers, technicians, or motorists that supports your classification. Your evidence may include temperature data, phase observations, composition analysis, or energy considerations.
(c) Choose one step you classified as a chemical change and write a balanced symbolic or word equation that represents the chemical transformation occurring.
(d) Suppose an engineer proposes operating the fractionating column at 250 °C instead of 400 °C. Predict how this adjustment would affect the type(s) of change occurring in step 1 and justify your answer in terms of intermolecular forces and vapor-liquid equilibrium.