Question 1: Define an alkene and describe one characteristic feature that distinguishes it from an alkane.

Answer: An alkene is a hydrocarbon with at least one carbon-carbon double bond; it is characterized by its unsaturation, which allows it to undergo addition reactions.

Question 2: Explain the general mechanism of an addition reaction of alkenes with hydrogen halides (HX).

Answer: In an addition reaction with HX, the alkene's carbon-carbon double bond opens up, with the hydrogen attaching to one carbon and the halide (X) attaching to the other, following Markovnikov's rule, where the hydrogen attaches to the carbon with more hydrogen atoms, and the halide attaches to the carbon with fewer hydrogen atoms.

Question 3: Calculate the amount of hydrogen gas (H₂) needed to completely hydrogenate 2 moles of ethene (C₂H₄). Use the reaction: C₂H₄ + H₂ → C₂H₆.

Answer: 2 moles of H₂ are needed to hydrogenate 2 moles of ethene.

Question 4: List two safety precautions that should be taken when handling alkenes in the laboratory.

Answer: Wearing appropriate gloves and safety goggles; working in a well-ventilated area or fume hood to avoid inhaling vapors.

Question 5: Describe a practical experiment to observe the addition of bromine (Br₂) to an alkene. Include the main variables involved.

Answer: In the experiment, an alkene such as ethene is placed in a test tube, and a few drops of bromine water are added. The mixture is shaken and observed for a color change from brownish-orange to colorless, indicating addition. The independent variable is the presence of the alkene, the dependent variable is the color change, and control variables include temperature and amount of bromine water used.

Question 6: What is the significance of the double bond in alkenes for their chemical reactivity?

Answer: The double bond contains a pi bond that is more reactive than a single bond, allowing alkenes to easily undergo addition reactions with various reagents.

Question 7: Identify the main industrial application of alkene addition reactions in the production of plastics.

Answer: Alkenes are used in polymerization processes to produce plastics like polyethylene and polypropylene.

Question 8: Explain how the reactivity of alkenes differs from that of alkanes.

Answer: Alkenes are more reactive than alkanes because of their double bonds, which contain pi bonds that are less stable and more susceptible to attack by reagents, enabling addition reactions. Alkanes have only single sigma bonds, making them less reactive and more stable.

Question 9: Fill in the blank: The addition of bromine water to an alkene results in a ___________ product, which indicates the presence of an unsaturated compound.

Answer: bromine

Question 10: Describe a real-life application where understanding the reactions of alkenes can be beneficial.

Answer: Understanding alkene reactions is crucial in the petrochemical industry for producing plastics, lubricants, and other chemicals. For example, the synthesis of polyethylene relies on the addition polymerization of ethene, which is fundamental for manufacturing packaging materials and containers.