Chapter 11 – Thermal Properties of Matter

1.

When thermal energy is supplied to melt a solid, the temperature remained constant during the melting point. Explain what happened to the heat energy supplied.

  • During melting, thermal energy absorbed is used to break the intermolecular bonds between the particles, resulting in increase in potential energy of the substance.

  • Thermal energy is not used to cause an increase in kinetic energy of the particles, hence temperature remains constant.

2.

*Using the kinetic model of gases, explain why evaporation of a liquid causes a fall in temperature.

  • In a sample of water, the molecules move at different speeds, and therefore different kinetic energies.

  • At the water surface, molecules with sufficient energy to overcome the attractive forces of other molecules escape into the atmosphere.

  • When energetic molecules escapes from the surface of a liquid, its leaves behind the less energetic molecules.

  • As a result, the average kinetic energy of the remaining molecules decreases and therefore the temperature of liquid falls.

3.

Which will cause a more severe injury? Scalding by boiling water at 100 degree Celsius or steam at 100 degree Celsius?

  • Scalding by steam at 100 degree Celsius.

  • Although both are of the same temperature, the latent heat of vaporization of steam is greater than specific heat capacity of water.

  • A larger amount of latent heat of vaporization is released as steam condenses on the skin, as compare to thermal energy released as water contacts the skin.