Help! 1.How much heat is required to convert 250mL of water from 20o
C into steam at 115o C?

2. From the phase diagram for water (Figure 10.31), determine the sate of water at: -20o

C and 40 kPa.

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.