Lesson test: Real substances

Sign in

Libre University uses your GitHub account. Signing in is only needed to sit a final test, so the score is kept on your profile.

Real substances

1.[2p]
Why can the ideal gas model never describe condensation?

Solving $v = R T / p$ gives one smoothly varying volume at every state, so there is no abrupt collapse to a liquid

Correct

It ignores gravity, which is what pulls a condensing liquid downwards

The answer is: Solving $v = R T / p$ gives one smoothly varying volume at every state, so there is no abrupt collapse to a liquid

It assumes constant specific heats, and latent heat requires them to vary

The answer is: Solving $v = R T / p$ gives one smoothly varying volume at every state, so there is no abrupt collapse to a liquid

It applies only to monatomic gases, and only polyatomic ones condense

The answer is: Solving $v = R T / p$ gives one smoothly varying volume at every state, so there is no abrupt collapse to a liquid

2.[3p]
Inside the saturation dome, why are pressure and temperature not enough to fix the state?

They are not independent there, since one determines the other along the saturation curve

Correct

They are independent, but the tables are not accurate enough to use them

The answer is: They are not independent there, since one determines the other along the saturation curve

Temperature is undefined while a substance is boiling

The answer is: They are not independent there, since one determines the other along the saturation curve

Pressure varies continuously during boiling, so it cannot be quoted

The answer is: They are not independent there, since one determines the other along the saturation curve

3.[1p]
Water's fusion line slopes backwards on the $p$ - $T$ diagram because ice is less dense than liquid water.

True

Correct

False

The answer is: True

4.[3p]
A rigid vessel of volume $0.500$ m³ holds $5.00$ kg of water at $100$ kPa, where $v_{f} = 0.001043$ and $v_{g} = 1.694$ m³/kg. What is the quality, as a fraction between 0 and 1?

CorrectNot quite: 0.0585

5.[2p]
Using the same saturation values at $100$ kPa, what is the specific volume in m³/kg of a mixture of quality $x = 0.50$ ?

CorrectNot quite: 0.848

6.[3p]
A sealed rigid vessel holds a saturated mixture whose specific volume is well above the critical value. As it is heated, what happens?

The quality rises, the liquid level falls, and the contents end up as superheated vapour

Correct

The quality falls, the liquid level rises, and the contents end up as compressed liquid

The answer is: The quality rises, the liquid level falls, and the contents end up as superheated vapour

The quality stays fixed, since the volume cannot change

The answer is: The quality rises, the liquid level falls, and the contents end up as superheated vapour

The state moves horizontally along the isotherm it started on

The answer is: The quality rises, the liquid level falls, and the contents end up as superheated vapour

7.[2p]
Under which conditions is the ideal gas model safe, meaning $Z$ within about one per cent of 1?

Select all that apply

Reduced pressure well below $0.1$

Correct

Reduced temperature above about $2$ at moderate pressure

Correct

Any state on the saturated vapour line

The answer is: Reduced pressure well below $0.1$ , Reduced temperature above about $2$ at moderate pressure

Any state at the critical point

The answer is: Reduced pressure well below $0.1$ , Reduced temperature above about $2$ at moderate pressure

8.[2p]
Match each term to what it corrects or describes.

$b$ in the van der Waals equation
$a / v^{2}$ in the van der Waals equation
The Maxwell construction
The critical point

the volume the molecules themselves occupy
where liquid and vapour cease to be distinguishable
attraction reducing the pressure felt at the wall
replacing the unphysical subcritical loop with a flat line

Show the answer

$b$ in the van der Waals equation: the volume the molecules themselves occupy $a / v^{2}$ in the van der Waals equation: attraction reducing the pressure felt at the wall The Maxwell construction: replacing the unphysical subcritical loop with a flat line The critical point: where liquid and vapour cease to be distinguishable

9.[2p]
Put these states of water at $100$ kPa in order of increasing specific volume.

Superheated steam at $150$ degrees Celsius
Compressed liquid
Saturated mixture of quality $0.06$
Saturated vapour

Show the answer

a, b, c, d

1.[2p] Why can the ideal gas model never describe condensation?

2.[3p] Inside the saturation dome, why are pressure and temperature not enough to fix the state?

3.[1p] Water's fusion line slopes backwards on the p-T diagram because ice is less dense than liquid water.

4.[3p] A rigid vessel of volume 0.500 m³ holds 5.00 kg of water at 100 kPa, where vf=0.001043 and vg=1.694 m³/kg. What is the quality, as a fraction between 0 and 1?

5.[2p] Using the same saturation values at 100 kPa, what is the specific volume in m³/kg of a mixture of quality x=0.50?

6.[3p] A sealed rigid vessel holds a saturated mixture whose specific volume is well above the critical value. As it is heated, what happens?

7.[2p] Under which conditions is the ideal gas model safe, meaning Z within about one per cent of 1?

8.[2p] Match each term to what it corrects or describes.

9.[2p] Put these states of water at 100 kPa in order of increasing specific volume.

1.[2p]
Why can the ideal gas model never describe condensation?

2.[3p]
Inside the saturation dome, why are pressure and temperature not enough to fix the state?

3.[1p]
Water's fusion line slopes backwards on the $p$ - $T$ diagram because ice is less dense than liquid water.

4.[3p]
A rigid vessel of volume $0.500$ m³ holds $5.00$ kg of water at $100$ kPa, where $v_{f} = 0.001043$ and $v_{g} = 1.694$ m³/kg. What is the quality, as a fraction between 0 and 1?

5.[2p]
Using the same saturation values at $100$ kPa, what is the specific volume in m³/kg of a mixture of quality $x = 0.50$ ?

6.[3p]
A sealed rigid vessel holds a saturated mixture whose specific volume is well above the critical value. As it is heated, what happens?

7.[2p]
Under which conditions is the ideal gas model safe, meaning $Z$ within about one per cent of 1?

8.[2p]
Match each term to what it corrects or describes.

9.[2p]
Put these states of water at $100$ kPa in order of increasing specific volume.