Question

when heat energy is added, two changes are observed: change a: solid changes to a liquid. change b: solid changes directly to a gas. what are the names for phase changes a and b? a is freezing and b is condensation. a is freezing and b is sublimation. a is melting and b is condensation. a is melting and b is sublimation.

Explanation:

1. Analyze Change A: When a solid changes to a liquid upon heat addition, this process is melting (solid → liquid, endothermic as heat is added). Freezing is liquid → solid (exothermic, heat removed), so A can't be freezing.
2. Analyze Change B: When a solid changes directly to a gas upon heat addition, this process is sublimation (solid → gas, endothermic). Condensation is gas → liquid (exothermic, heat removed), so B can't be condensation.
3. Check the options:

• First option: A is freezing (incorrect, as freezing is heat removal), B is condensation (incorrect). Eliminate.
• Second option: A is freezing (incorrect), B is sublimation (B is correct, but A is wrong). Eliminate.
• Third option: A is melting (correct, solid→liquid with heat), B is condensation (incorrect, condensation is gas→liquid). Eliminate.
• Fourth option: A is melting (correct, solid→liquid with heat), B is sublimation (correct, solid→gas with heat). This matches the heat - added conditions for both changes.

Answer:

A is melting and B is sublimation. (The option corresponding to "A is melting and B is sublimation" among the given choices)