What is the boiling point of water at standard atmospheric pressure (in degrees Celsius)?

What is the boiling point of water at standard atmospheric pressure (in degrees Celsius)?

• A. 90 °C
• B. 110 °C
• C. 120 °C
• D. 100 °C

Answer: (D)

The main idea is the boiling point: the temperature at which a liquid’s vapor pressure equals the surrounding pressure. At standard atmospheric pressure (about 1 atmosphere, 101.3 kPa), water’s vapor pressure reaches that external pressure at roughly 100 °C, so it begins to form bubbles throughout the liquid and boil. That makes 100 °C the boiling point under these conditions. If the pressure were higher, water would boil at a higher temperature; if lower, at a lower temperature. The other temperatures would correspond to different pressures, not standard atmospheric pressure.

The main idea is the boiling point: the temperature at which a liquid’s vapor pressure equals the surrounding pressure. At standard atmospheric pressure (about 1 atmosphere, 101.3 kPa), water’s vapor pressure reaches that external pressure at roughly 100 °C, so it begins to form bubbles throughout the liquid and boil. That makes 100 °C the boiling point under these conditions. If the pressure were higher, water would boil at a higher temperature; if lower, at a lower temperature. The other temperatures would correspond to different pressures, not standard atmospheric pressure.