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. hydrogen gas reacts with ethane to make ethylene. high temperatures are required to make ethylene. the synthesis of ethylene is a chemical change. steam cracking breaks smaller molecules into larger molecules.

Explanation:

1. The text states that ethane decomposes at high - temperatures to make hydrogen gas and ethylene, not that hydrogen gas reacts with ethane to make ethylene. So the first statement is false.
2. It is mentioned that fossil fuels are heated to up to 900°C for steam cracking and ethane decomposes at high temperatures to form ethylene, indicating high temperatures are required. So the second statement is true.
3. The synthesis of ethylene from ethane involves a chemical reaction where new substances are formed, which is a chemical change. So the third statement is true.
4. Steam cracking breaks large carbon - based molecules into smaller molecules, not the other way around. So the fourth statement is false.

Answer:

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