How does the addition of thermal energy affect the molecules in a substance?

• A. It decreases the average kinetic energy of the molecules.
• B. It increases the average kinetic energy of the molecules.
• C. It causes the molecules to lose mass.
• D. It makes the molecules form chemical bonds spontaneously.

Answer: (B)

Verified step by step guidance

1. Understand that thermal energy is related to the energy of motion of molecules in a substance.
2. Recall that the average kinetic energy of molecules is directly proportional to the temperature of the substance.
3. Recognize that adding thermal energy means increasing the temperature, which increases the speed and movement of molecules.
4. Conclude that as thermal energy is added, the average kinetic energy of the molecules increases, causing them to move faster.
5. Note that adding thermal energy does not change the mass of molecules or cause spontaneous formation of chemical bonds under normal conditions.