Question

16. The the following questions refer to above phase diagram. (6 pts.) a. What process in moving from A occurs to C? Temperature b. What is the intersection at D called? c. Which letter is the liquid phase? d. What process occurs to the right of point D as pressure increases? e. What process occurs if you increase pressure on the solid? 1. If one atmosphere of pressure is higher than D. what happens when the solid is heated?

Answer 1

Phase diagrams are graphical representation of physical states of a substances under different conditions of pressure and temperature. It gives us information about the change of states and also to understand which all states (or phases) are present in a given temperature and pressure.

Now let us look and understand the given phase diagram.

Phase diagrams mainly has three areas to look upon

Area marked A, represents solid .state

Area marked B,represents liquid state

Area marked C, represents gas state (or vapour phase).

Now there are three lines in the diagram.

The line between A and B represent a solid-liquid equilibrium (where solid and liquid coexist)

The line between B and C represent liquid-vapour equilibrium (where liquid and gas coexist)

The line between A and C represent solid- vapour equilibrium (where solid and gas coexist)

Change of state from solid to liquid is called melting

Change of state from liquid to solid is termed freezing

change of state from liquid to gas is termed vapourisation

Change of state from gas to liquid is termed condensation

Change of state from solid to gas is termed sublimation

Now let us look into questions

a) A represents solid phase and C represent gaseous phase. SO when we are moving fro A to C solid state is changing to gaseous state without getting convert into liquid state. This process by which solid state is converted to gaseous state without getting converted into liquid state is called sublimation.

So the process that occurs on moving from A to C is sublimation. You can do that either by increasing the temperature of the solid or by decreasing the pressure

b) D is the triple point.Triple point is the temperature and pressure att which gas, liquid and solid exists in thermodynamic equilibrium.

We can see that in D all the three lines meet and hence all phases should be in equilibrium together.

c) As said above B represent liquid phase

d)The line representing the right side of D is liquid - vapour equilibrium. So as we increase pressure we reach the B region which represents liquid state. That means gas changes to liquid or condensation takes place.