A characteristic property of a substance is a property that does not depend on the amount (mass) of the substance. It can be used to identify a substance.

     Melting point, freezing point, and boiling point are characteristic properties of chemical substances.When a solid substance is heated, it will reach a specific temperature at which it begins to melt (become liquid). This is it's melting point. When a liquid is cooled, it reaches a temperature at which it begins to freeze (become solid). This is its freezing point. Generally, for a particular substance, the melting point temperature and freezing point temperature are the same.

     When a liquid is heated, it will reach a temperature at which it begins to become a gas. This is it's boiling point. The process in which a liquid becomes a gas is called evaporation. The opposite process, in which a gas becomes a liquid, is called condensation.

     A phase change graph shows that at the melting point or at the boiling point there is no increase in temperature. A"plateau"in temperature forms and the temperature stays the same until all of the substance has melted or boiled. The heat energy that is added does not increase the temperature. The heat energy is used to speed up the particles and move the particles farther apart.

     The melting, freezing, and boiling point temperatures of a substance are physical properties useful to a scientist. They can be used in the identification of an unknown substance. They can also be used to predict the phase (state) of matter a substance will be in at any temperature. If the temperature of a substance is below the melting point, it will be a solid. If the temperature of a substance is between the melting point and the boiling point, it will be a liquid. If the temperature of a substance is above the boiling point, it will be a gas.