Question

What phase change can water undergo as the temperature changes from -5 oC to 25 oC at a constant pressure of 0.2 kPa?

Answer 1

Please refer to water phase diagram from your book.

If move across along the pressure axis (y axis) stope at 0.2 kPa. From this point move horizontally along the x axis (constant pressure), the temperatures and the pressure indicate we have ice and water vapor equilibrium.

This indicates that an increase in temperature from -5 to 25 degrees will sublime the water (ie convert water to vapor without passing through a liquid phase).

So the phase change is from ice to water vapor.