91Ó°ÊÓ

1. The mass of sample A of liquid water and mass of sample B of ice are identical.
2. The graphs (b), (c), (d), (e) and (f) of Figure 18-25.

When an object's temperature changes, it expands and grows larger, a process known as thermal expansion. The sudden drop in temperature of the ice or water at equilibrium is impossible. From this, we can find which situation is shown in the graph is impossible. From the given Graphs, b, c, d, e, and f of figure 18-25, we can find whether the equilibrium temperature is above, below, or at the freezing point of the water, and the liquid partly freezes, fully freezes, or undergoes no freezing, and also whether ice partly melts, fully melts, and undergoes no melting.

Formula:

At equilibrium point, the temperature relation is given by:${\left({\mathrm{T}}_{\mathrm{f}}-{\mathrm{T}}_{\mathrm{i}}\right)}_{\mathrm{A}}={\left({\mathrm{T}}_{\mathrm{f}}-{\mathrm{T}}_{\mathrm{i}}\right)}_{\mathrm{B}}$ …(¾±)

where, ${\mathrm{T}}_{\mathrm{f}}$is the final temperature, ${\mathrm{T}}_{\mathrm{i}}$is the initial temperature and ${\left({\mathrm{T}}_{\mathrm{f}}-{\mathrm{T}}_{\mathrm{i}}\right)}_{\mathrm{A}}$ and ${\left({\mathrm{T}}_{\mathrm{f}}-{\mathrm{T}}_{\mathrm{i}}\right)}_{\mathrm{B}}$of sample A and B respectively.

We note that, the rise in temperature of sample B of ice is equals to the loss in the temperature of sample A of liquid water, and the temperature of sample A and B equals at equilibrium. Thus, at equilibrium point, the temperature relation is given by using equation (i).

Also, we know that ${\mathrm{Q}}_{\mathrm{A}}>{\mathrm{Q}}_{\mathrm{B}}$.

The situation in Graph (f) of Figure 18-25 is impossible because the sudden drop in temperature T of the ice or water at equilibrium is impossible and temperature of the ice will not rise to freezing point and then drop.

Fromthe Graph (b) and (c) of Figure 18-25, we can observe that at equilibrium, the horizontal line is at the same temperature-at the point where the two graphs meet. Hence, the equilibrium temperature is at freezing point.

But in case of Graph (d) of Figure 18-25, we can observe that at equilibrium, the horizontal line is below the temperature at the point where the two-graph meet. Hence, the equilibrium temperature is above the freezing point.

In case of Graph (e) of Figure 18-25, we can observe that at the equilibrium, the horizontal line is above the temperature at the point where the two-graphs meet.

Hence, the equilibrium temperature is below the freezing point.

From Graph (b) of Figure 18-25, we can observe that there is horizontal section in the water graph before it meets with ice graph. Hence, water partly freezes. Also, from Graph (b) of Figure 18-25, we can observe that there is no horizontal line for the ice graph before meeting point, hence, there is no phase change, and therefore, we can say that theice undergoes no melting.

Similarly, From Graph (c) of Figure 18-25, we can observe that there is no horizontal section of the water graph before it meets with ice graph. Hence, water undergoes no freezing. Also, from Graph (c) of Figure 18-25, we can observe that there is no horizontal line for the ice graph before meeting point, hence there is no phase change, and therefore. we can say that theice undergoes no melting.

From Graph (d) of Figure 18-25, we can observe that there is no horizontal section of the water graph before it meets with the ice graph. Hence, water undergoes no freezing. Also, from Graph (d) of Figure 18-25, we can observe that there is a horizontal line for the ice graph before meeting point, hence, there is a phase change and therefore, we can say that, theice undergoes fully melting.

And from Graph (e) of Figure 18-25, we can observe that there is a horizontal section of the water graph before it meets the ice graph. Hence, water undergoes fully freezing. Also, from Graph (e) of Figure 18-25, we can observe that there is no horizontal line for the ice graph before meeting point, hence, there is no phase change, and therefore, we can say that the ice undergoes no melting.