Question 1: Define an addition reaction in the context of organic chemistry involving alkenes.

Answer: An addition reaction is a chemical process where atoms or groups of atoms are added to the carbon atoms of an alkene's double bond, resulting in a saturated compound.

Question 2: Explain the mechanism of electrophilic addition to an alkene.

Answer: Electrophilic addition involves the attack of a positively charged species (electrophile) on the electron-rich double bond of an alkene. First, the electrophile reacts with the alkene to form a carbocation intermediate. Then, a nucleophile or another atom/group adds to the carbocation, resulting in a saturated product.

Question 3: Identify the main products formed when ethene reacts with hydrogen bromide (HBr).

Answer: The main product is bromoethane (ethyl bromide).

Question 4: Calculate the amount of hydrogen (in grams) needed to fully hydrogenate 50 g of ethene.

Answer: Moles of ethene = 50 g / 28.04 g/mol ≈ 1.78 mol. Since hydrogenation involves 1 mol of H₂ per mol of ethene, grams of H₂ = 1.78 mol × 2.02 g/mol ≈ 3.60 g.

Question 5: Which of the following reagents would cause an addition reaction with an alkene? A) Bromine (Br₂) B) Water (H₂O) C) Both A and B D) Neither A nor B

Answer: C) Both A and B

Question 6: Fill in the blank: When alkenes react with halogens like chlorine or bromine, the reaction is called ________ addition.

Answer: halogen

Question 7: Describe a practical industrial application of addition reactions involving alkenes.

Answer: Addition reactions are used in the production of polymers, such as polyethylene, where ethene molecules undergo addition polymerisation to form long-chain plastics.

Question 8: Identify the variables that need to be controlled during an experiment to add hydrogen to an alkene safely.

Answer: Variables include temperature, pressure, catalyst presence, and ensuring proper ventilation to prevent hydrogen accumulation and reduce explosion risk.

Question 9: Analyse the following scenario: Ethene reacts with bromine water, turning from orange to colourless. Explain what this indicates about the reaction.

Answer: The decolourisation of bromine water indicates that an addition reaction has taken place, where bromine adds across the double bond of ethene, converting it into a colourless dibromoalkane. This confirms the presence of an alkene functional group.

Question 10: Explain why addition reactions are important in the manufacturing of pharmaceuticals.

Answer: Addition reactions allow the modification of organic molecules to synthesize complex pharmaceutical compounds, enabling the development of drugs with specific biological activities.