Consider adding enough heat to a solid sample of a substance below its melting point to change the sample to the gas above its boiling point. Which of the following would involve no change in temperature of the sample as the described transition occurs?

• A. Heating the initial sample to its melting point.
• B. Heating the sample and converting the liquid to the gas at the boiling point.
• C. Heating the liquid at the melting point to the liquid at the boiling point.
• D. Heating the gas above the boiling point.

Answer: (B)

Verified step by step guidance

1. Identify the different phases involved in the transition: solid, liquid, and gas.
2. Understand that during phase changes (solid to liquid and liquid to gas), the temperature of the substance remains constant even though heat is being added. This is because the energy is used to overcome intermolecular forces rather than increasing temperature.
3. Recognize that the transition from solid to liquid occurs at the melting point, and the transition from liquid to gas occurs at the boiling point.
4. Note that heating the sample to its melting point or heating the liquid to its boiling point involves a temperature change until the phase change begins.
5. Conclude that the process involving no change in temperature is the conversion of the liquid to the gas at the boiling point, as this is a phase change where the temperature remains constant.