Question

to make polyethylene, its monomer ethylene must first be synthesized from fossil fuels. petroleum and natural gas are broken into smaller molecules through a process called steam cracking. during this process, fossil fuels are heated to temperatures up to 900°c. large carbon - based molecules are broken apart, or \cracked,\ to produce small molecules like ethane. once ethane is made, it decomposes due to the high temperatures to make hydrogen gas and ethylene. select the true statements. steam cracking turns smaller molecules into larger molecules. high temperatures are required to make ethylene. the synthesis of ethylene is a chemical change. hydrogen gas reacts with ethane to make ethylene.

Explanation:

1. Steam cracking breaks large - carbon based molecules into smaller ones, not the other way around, so the first statement is false.
2. The text states that fossil fuels are heated to up to 900°C for the process, and ethane decomposes at high temperatures to make ethylene, so high temperatures are required to make ethylene.
3. The synthesis of ethylene from ethane involves a change in chemical structure, which is a chemical change.
4. The text says ethane decomposes to make hydrogen gas and ethylene, not that hydrogen gas reacts with ethane to make ethylene. So only the second and third statements are true.

Answer:

High temperatures are required to make ethylene.
The synthesis of ethylene is a chemical change.