Heating increases molecular kinetic energy but decreases potential energy in solids

Steps:

• Heating the aluminum block raises its temperature, increasing the average translational and vibrational kinetic energy of atoms.
• Higher kinetic energy causes atoms to vibrate with greater amplitude, leading to thermal expansion and increased average interatomic distances.
• Expansion reduces the strength of attractive forces between atoms, making the potential energy less negative (decreases in magnitude).
• Therefore, kinetic energy increases while potential energy decreases.

Why A is correct:

• Kinetic energy rises with temperature per the kinetic theory (average KE = 3/2 kT for translational modes), and expansion decreases potential energy by weakening attractions.

Why the others are wrong:

• B: Potential energy increases with separation (less bound), not decreases.
• C: Kinetic energy cannot decrease when heating.
• D: Both energies increase or kinetic decreases, contradicting heating effects.

Final answer: A