Question

Some water is placed in a sealed glass container connected to a vacuum pump (a device used to pump gases from a container), and the pump is turned on. The water appears to boil and then freezes. Explain these changes by using the phase diagram for water. What would happen to the ice if the vacuum pump was left on indefinitely?

Short answer

The boiling of the liquid takes place because of the decrease in the pressure leading to the boiling action. Boiling is an endothermic reaction where the temperature eventually drops and changes the gas state from liquid to solid. In the case of water, it converts to ice because a reduction in pressure leads to a reduction in temperature.

Step-by-step solution

Phase diagram

A phase diagram is a convenient way of representing the phases of a substance as a function of temperature and pressure.It is essential to recognize that a phase diagram describes conditions and events for a pure substance in a closedsystem of the type where no material can escape into the surroundings and no air is present.

Phase diagram of water

Explanation

As shown in the phase diagram, that change in the liquid to gas phase occurs only when there is a decrease in pressure and an increase in temperature. This leads to the boiling effect of the water. As previously mentioned, boiling is endothermic; it tends to absorb all the heat in the surrounding of the containing, leading to a drop in temperature in the surrounding of the container.

The drop in the temperature starts to freeze the liquid/gas or, in this case, vapor gas. The decreased temperature freezes the liquid/ water and turns it into ice.

An endothermic reaction is a process that absorbs heat from its surroundings.The absorbed energy serves as the activation energy for the reaction.

The boiling of the liquid takes place because of the decrease in the pressure leading to the boiling action. Boiling is an endothermic reaction where the temperature eventually drops and leads to the change of the gas state from liquid to solid. In the case of water, it converts to ice because a reduction in pressure leads to a reduction in temperature.