When heat is added to a system, which may occur?

• A. The temperature may increase, and the substance may change state
• B. The substance becomes colder
• C. The temperature may decrease
• D. Only the color changes

Answer: (A)

When heat is added, energy flows into the system and increases the average kinetic energy of the particles, which raises temperature. If enough energy is supplied, the particles can overcome intermolecular forces and change how they are arranged, causing a state change like solid to liquid (melting) or liquid to gas (boiling). It’s also useful to note that during a phase change, the added energy goes into changing the state, so the temperature may stay the same temporarily until the transition is complete, then rise again with further heating. The idea that heat makes something colder or only changes color doesn’t fit the general effect of adding heat.