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What phase changes occur if the temperature of a system is increased while the pressure if held constant?

A sample of liquid water at atmospheric pressure has a temperature just above freezing point. 1. what Phase changes occur if the temperature of the system is increased while the pressure is held constant. 2. Suppose, instead that the temperature of the system is held constant just above the freezing point while the pressure is decreased. What phase changes occur now?

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1. For (1), the system will undergo a phase transition from the liquid to the gaseous state if temperature is increased at constant pressure. For (2), you need to recognize that water is unusual, in that the slope of the solid-liquid phase boundary is negative (if pressure is plotted on the vertical axis, and temperature on the horizontal axis). That means that reducing the pressure on a sample of liquid water near the1-atm freezing temperature will first cause sample to freeze (undergo a transition from the liquid to the solid phase). As the pressure is decreased further, the pressure will eventually drop below the vapor pressure of solid water at the relevant temperature, and the water will sublimate (undergo a phase transition from the solid to the gaseous state).