How does the boiling point of water relate to vacuum pressure?

• A. The boiling point increases with higher vacuum pressure
• B. The boiling point remains constant regardless of vacuum pressure
• C. The boiling point decreases as vacuum pressure increases
• D. The boiling point can only be affected by temperature, not pressure

Answer: (C)

The relationship between the boiling point of a liquid and the pressure exerted on it is fundamental in understanding phase changes. In the case of water, as vacuum pressure increases (which means the pressure is lower than atmospheric pressure), the boiling point of water decreases. This is due to the fact that boiling occurs when the vapor pressure of the liquid equals the surrounding pressure.

Under lower pressures, such as those created in a vacuum, water does not need to reach as high a temperature for its vapor pressure to match the pressure surrounding it. Consequently, water will boil at a lower temperature when in a vacuum. This principle is often utilized in various applications like vacuum distillation, where substances can be separated at lower temperatures to prevent thermal degradation.

The other options do not accurately describe the relationship between boiling point and pressure. For instance, higher vacuum pressure would actually correlate with lower boiling points, contradicting the first option. Additionally, the boiling point does change with variations in pressure, so it cannot be constant, and boiling point is indeed affected by both temperature and pressure, countering the idea that temperature is the only influencing factor.