STUDENT SPACE · TOPIC 4

Alkane and alkene reactions

Use observations and equations to distinguish substitution and addition.

The essentials

Alkanes are saturated hydrocarbons with single covalent bonds. They are generally unreactive.
CH₄ + Cl₂ → CH₃Cl + HCl. Ultraviolet light provides activation energy.
Aqueous bromine changes from orange to colourless with an alkene. An alkane gives no change under normal test conditions.
Ethene + H₂ → ethane, using a nickel catalyst. Ethene + steam → ethanol, using an acid catalyst.

Try each question before opening its hint or answer. Use paper for calculations and diagrams.

What observation distinguishes hexane from hexene using aqueous bromine?

Need a hint for Question 1?

For addition, open C=C to C–C and attach the new atoms without losing existing atoms.

Check Question 1

Hexene decolourises it. Hexane leaves it orange under normal test conditions.

Write the equation for monosubstitution of ethane by chlorine and give the condition.

Need a hint for Question 2?

Replace just one hydrogen atom with chlorine.

Check Question 2

C₂H₆ + Cl₂ → C₂H₅Cl + HCl. Ultraviolet light.

Draw the displayed product of hydrogen addition to ethene. Name the catalyst.

Need a hint for Question 3?

Open the C=C bond and add one H to each carbon.

Check Question 3

Ethane, CH₃CH₃. Show all single bonds. Nickel catalyst.

Use Lesson 4 in your worksheet for written practice. Your teacher will discuss those answers in class.