If a substance has low vapor pressure, what is its likely boiling point tendency?

If a substance has low vapor pressure, what is its likely boiling point tendency?

• A. It tends to have a high boiling point.
• B. It tends to have a low boiling point.
• C. It boils at room temperature.
• D. It is always nonvolatile.

Answer: (A)

Low vapor pressure means the substance is not easily converted into vapor because its molecules are held together by stronger intermolecular forces. The boiling point is the temperature at which a liquid’s vapor pressure equals the surrounding atmospheric pressure. If the vapor pressure is low, you must raise the temperature higher to reach that balance, so the substance tends to have a higher boiling point. For example, water has a relatively low vapor pressure at room temperature and boils only when heated to 100°C at 1 atm. Substances with high vapor pressure at room temperature vaporize more readily and have lower boiling points. Therefore, a substance with low vapor pressure is best described as having a high boiling point tendency.

Low vapor pressure means the substance is not easily converted into vapor because its molecules are held together by stronger intermolecular forces. The boiling point is the temperature at which a liquid’s vapor pressure equals the surrounding atmospheric pressure. If the vapor pressure is low, you must raise the temperature higher to reach that balance, so the substance tends to have a higher boiling point. For example, water has a relatively low vapor pressure at room temperature and boils only when heated to 100°C at 1 atm. Substances with high vapor pressure at room temperature vaporize more readily and have lower boiling points. Therefore, a substance with low vapor pressure is best described as having a high boiling point tendency.