The energy is absorbed during which phase change for bromine?

• A. Br2(l) -> Br2(g)
• B. Br2(g) -> Br2(l)
• C. Br2(s) -> Br2(l)
• D. Br2(g) -> Br2(s)

Answer: (A)

Endothermic phase changes require energy input to move to a higher-energy state. Bromine is a liquid under ordinary conditions, so turning it into a gas means vaporization, which requires adding heat to overcome intermolecular forces. That energy absorption is what makes this change the correct one. The other transitions involve energy release (gas to liquid is condensation, gas to solid is deposition), or would occur only if bromine were in a different phase than it typically is under standard conditions (solid to liquid). So the phase change that absorbs energy is liquid bromine becoming gaseous bromine.