Which of the following best describes the chemical decomposition of aluminum chloride (AlCl_3) when heated?

• A. AlCl_3 decomposes to form aluminum metal and chlorine gas.
• B. AlCl_3 decomposes to form AlCl_2 and Cl_2 gas.
• C. AlCl_3 sublimes without significant decomposition under normal conditions.
• D. AlCl_3 decomposes to form Al_2O_3 and HCl gas.

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the nature of aluminum chloride (AlCl_3). It is a covalent compound that tends to sublime (transition from solid to gas) rather than decompose easily when heated under normal conditions.
2. Step 2: Consider the typical behavior of AlCl_3 upon heating. Instead of breaking down into simpler substances like aluminum metal or chlorine gas, AlCl_3 usually changes phase directly from solid to gas without significant chemical change.
3. Step 3: Analyze the proposed decomposition reactions: forming aluminum metal and chlorine gas would require a reduction process, which is not typical for AlCl_3 upon heating alone; forming AlCl_2 and Cl_2 gas is not a common or stable decomposition pathway; forming Al_2O_3 and HCl gas would require the presence of oxygen and moisture, which is not indicated here.
4. Step 4: Recognize that the correct description is that AlCl_3 sublimes without significant decomposition under normal heating conditions, meaning it transitions to gas phase intact rather than breaking down chemically.
5. Step 5: Conclude that the best description of AlCl_3 behavior when heated is sublimation without significant decomposition, consistent with its known physical and chemical properties.