QCM : Hydrocarbon Chemistry and Cracking — 10 questions

Explication

Crude oil is mainly composed of a mixture of hydrocarbons, predominantly saturated alkanes, which have the general formula CnH2n+2. The other options are incorrect because crude oil is not composed of pure elements or other chemical families like alcohols or acids.

Explication

The fractional distillation process became a standard method for separating hydrocarbons in crude oil during the early 20th century, particularly in the 1910s, as refinements in petroleum refining techniques were developed and implemented worldwide.

Explication

Robert Boyle is credited with early contributions to experimental chemistry and techniques such as distillation. Although fractional distillation was developed through cumulative efforts over time, Boyle's work in the 17th century laid foundational principles for separating mixtures through physical methods. The other options, Dmitri Mendeleev, Marie Curie, and John Dalton, made significant contributions to chemistry but are not specifically credited with the discovery or proposal of fractional distillation.

Explication

The simplest alkene, and the first in the series, is ethene (C2H4). It is the fundamental alkene used as a starting material in many chemical reactions and is explicitly mentioned as the first alkene.

Explication

Shorter hydrocarbons are less viscous and vaporize at lower temperatures because their molecules are smaller and require less energy to vaporize. Longer hydrocarbons are more viscous and have higher boiling points due to their larger molecular size, which increases resistance to flow and the energy needed for vaporization.

Explication

Hydrocarbon combustion is a chemical reaction where hydrocarbons react with oxygen, producing carbon dioxide and water, and releasing energy. It is not a physical separation, cracking, or polymerization process.

Explication

Applying cracking in practice involves heating larger hydrocarbons with catalysts or steam at high temperatures to break the molecules into smaller ones, such as alkenes. The other options do not describe the cracking process and are not valid methods for producing alkenes from larger hydrocarbons.

Explication

The double bond in alkenes increases their reactivity, allowing them to participate in addition reactions, which is essential for producing polymers and other chemicals, thus fulfilling their role in chemical industry.

Explication

Cracking is a process that breaks down large hydrocarbons into smaller, more useful molecules like alkanes and alkenes, which are more suitable for fuels and chemical manufacturing. It does not produce larger molecules, increase saturation, or make hydrocarbons more viscous.

Explication

Cracking equations are characterized by breaking larger hydrocarbon molecules into smaller ones, ensuring that the total number of carbons and hydrogens remains the same on both sides of the equation. This conservation reflects the physical process of cracking, where atoms are rearranged but not added or removed in terms of total count.