The phase diagram for a pure substance is shown to the right. Use this diagram a

Question

The phase diagram for a pure substance is shown to the right. Use this diagram and your knowledge about changes of phase to answer the following question. What does point V represent? What characteristics are specific to the system only at point V? What does each point on the curve between V and W represent? Describe the changes that the system undergoes as the temperature slowly increase from X to Y to Z at 1.0 atmosphere. In a solid-liquid mixture of this substance, will the solid float or sink? Explain.

Explanation / Answer

ANSWER:

(a) The point V represents TRIPLE POINT. At this point all the THREE PHASES solid, liquid and gas are in equilibrium. The system is INVARIENT at point V.

(b) Each point on cuve VW represent equilibrium between LIQUID AND GAS PHASE. The region above the curve represent liquid phase and below it represents gas phase.

(c) The curve YV represents SUBLIMATION of the substance. The cuve separaes SOLID PHASE from GAS PHASE. When we go from X to Y temperature is increased but at reduced pressure. At point Y the substance to start to SUBLIME. If the temperature is further increased to Z, al the solid is changed to gas phase.

(d) he solid will SINK. Because we see from the solid-liquid mixture if the pressure is increased the melting point also increases. This is because as pressure is increased the equilibrium shifts to the side which results in lower pressure. In other words that phase will form that will occupy smaller volume. (HINT:LOWERING VOLUME MEANS INCREASING DENSITY) . In this case more solid is formed that is why melting point is increased to melt the solid.

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