In Sections 1.3 and 2.5A3, we noted that the physical properites of a particular substance determine its state at room temperature. If both its normal melting point and its normal boiling point are below room temperature (20°C), the substance is a gas under normal conditions. The normal melting point of oxygen is -218°C; its normal boiling point is -189°C. Oxygen is a gas at room temperature. If the normal melting point of a substance is below room temperature, the substance is a liquid at room temperature. Benzene melts at 6°C and boils at 80°C; it is a liquid at room temperature. If both the normal melting point and the normal boiling point are above room temperature, the substance is a solid. Sodium chloride melts at 801°C and boils at 1413°C. Sodium chloride is a solid under normal conditions. Figure 9.1 illustrates the relationship between physical state and normal melting and boiling points.
