During melting, which statement about temperature is true for a pure substance?

During melting, which statement about temperature is true for a pure substance?

• A. Temperature continues to rise as the solid melts.
• B. Temperature decreases during melting.
• C. Temperature remains constant while the solid changes to liquid.
• D. Temperature fluctuates unpredictably during melting.

Answer: (C)

At the melting point, the temperature of a pure substance stays constant while it changes from solid to liquid because the heat added goes into breaking the orderly solid structure (latent heat of fusion) rather than increasing the molecules’ kinetic energy. In other words, energy is used to convert solid into liquid, so the temperature doesn’t rise during the phase change. Once all the solid has melted, any additional heat then raises the temperature of the liquid.

At the melting point, the temperature of a pure substance stays constant while it changes from solid to liquid because the heat added goes into breaking the orderly solid structure (latent heat of fusion) rather than increasing the molecules’ kinetic energy. In other words, energy is used to convert solid into liquid, so the temperature doesn’t rise during the phase change. Once all the solid has melted, any additional heat then raises the temperature of the liquid.