NChem_Chapter 16 Alkanes and Alkenes

What is the name of this molecule?

• methane

• ethene

• butene

• butane

Answer explanation

1C-meth

2C-eth

3C-prop

4C-but

Which two hydrocarbons are alkanes?

(Hint: the general formula for alkanes is C_nH_2n+2)

• C₂H₆

• C₃H₈

• C₅H₁₂

• C₁₀H₄₂

Which of the following molecules has the highest boiling point?

• CH₄

• C₂H₆

• C₆H₁₄

• C₁₄H₂₈

Explain why the boiling point of alkanes increase down the series.

Answer: Going down the series, the number of carbon atoms increase. Alkane molecules increase in size. (a)   forces of attraction between alkene molecules become stronger, therefore more energy is required to overcome these stronger forces of attraction.

Which chemical reactions do alkenes participate in?

• Addition

• Substitution

• Combustion

• Cracking

Answer explanation

Alkanes are generally unreactive and participate in combustion and substitution reactions, as well as cracking.

Alkenes are more reactive and participate in addition reactions (e.g. bromination, hydrogenations).

An alkene burns in oxygen. The chemical reaction is shown below.

2C₂H₄ + 5O₂ --> 4CO + 4H₂O

Which type of combustion has occured?

• complete combustion

• incomplete combustion

Answer explanation

Complete combustion only produces CO₂ and H₂O.

Incomplete combustion produces other compounds like CO (carbon monoxide) and C (carbon, or soot)

Alkanes participate in substitution reactions. What are the conditions required for this reaction?

(a)  

Methane (CH₄) reacts with chlorine gas (Cl₂). Which two products are formed?

• CH₃Cl

• HCl

• CH₂Cl₂

• CCl₄

Ethene (C₂H₆) reacts with hydrogen gas (H₂). What is the product formed?

• 
• 
• 
• 

Answer explanation

This addition reaction is called hydrogenation.

The C=C double bond breaks and hydrogen is added to each carbon atom.

Ethene (C₂H₄) reacts with bromine (Br₂). Draw the product formed.

Answer explanation

This addition reaction is called bromination.