Final answer:
At a constant temperature of 100°C, an increase in pressure to 900 mmHg would result in an increased boiling point of water, meaning the water would not boil at the standard 100°C but would require a higher temperature to start vaporizing.
Step-by-step explanation:
If the temperature is kept constant at 100°C and the pressure rises from 0 mmHg to 900 mmHg, the water would remain in a liquid state at pressures up to the point where it reaches its new boiling point at a higher pressure. Normally, water boils at 100°C at 1 atmosphere of pressure (which is approximately 760 mmHg). However, if the pressure is increased to 900 mmHg while maintaining the temperature at 100°C, the boiling point of the water would actually increase.
Due to the elevated pressure, the molecules within the water would require more energy, i.e., a higher temperature, to escape from the liquid phase to the gaseous phase;
therefore, the water would not boil at 100°C under these conditions, based on the vapor pressure curve of water.
It is only when the temperature is increased beyond this new boiling point that water would begin to vaporize.