Thermodynamic Properties

Question 1

What is a pure substance?

Answer 1

A substance that has a fixed chemical composition throughout

Question 2

What happens as we heat a compressed liquid with a constant pressure from 20 degrees Celcuis to 300 degrees Celsuis at 1 atm?

Answer 2

• The temperature of the liquid increases linearly until it reaches the boiling point of 100 degrees Celcius
• At this temperature, we have a saturated liquid. as we continue to heat it, we create a saturated mixture because water begins to evaporate, meaning we have both saturated water and saturated vapour
• Once all of the water has boiled, then we will have completely saturated vapour. As we continue to heat the vapour, we will have superheated vapour
• As this process happens, the system will expand to ensure that we have a constant pressure

Question 3

If we continue to boil different samples of water at different pressures, what will we see?

Answer 3

We will see that the boiling temperature is greater at higher pressures

Question 4

What is Latent Heat?

Answer 4

This is the amount of energy absorbed during a phase change

Question 5

What are the two types of Latent Heats?

Answer 5

• Vaporization
• Fusion

Question 6

What is the triple point?

Answer 6

This is when the conditions of a pure substance allow all three phases to coexist in equilibrium

Question 7

How can we pass from the solid to vapour phase?

Answer 7

• Melt into a liquid, and then evaporate
• Evaporate directly without melting

Question 8

Where does a solid evaporating directly occur relative to the triple point value?

Answer 8

We will see a lower pressure because a pure substance can’t exist in the liquid phase at those pressures

Question 9

How can we determine the change in u in a thermodynamic system that we apply to heat to?

Answer 9

If we have a constant volume, then we can determine that the change in u = q

Question 10

How can we determine the change in h for a thermodynamic system that we apply heat to?

Answer 10

If we have a constant pressure, we know that the change in u = q - w
We can then state that because the pressure doesn’t change, then the change in h = q

Question 11

What approximation can we use for a compressed liquid using the saturated liquid tables?

Answer 11

We can say that the compressed liquid can be treated as a saturated liquid at the same temperature

Question 12

What are the equations for quality?

Answer 12

• x = Mass of vapour / Total Mass
• x = (Average specific volume - Specific volume of fluid) / Specific volume of fg