Carmelo

Question 1

What is the purpose of the compressibility factor Z?

Answer 1

Accounts for deviation from the ideal gas law

Question 2

What is the acentric factor?

Answer 2

Measures how non-spherical a molecule is. Spherical molecules such as noble gases has acentric factor = 0, as this increases molecules become less spherical. H2 has negative value due to its quantum effects

Question 3

When do gases significantly deviate from ideal gas behaviour?

Answer 3

Molecular interactions cause deviations so at lower temps or higher pressures when they are close together

Question 4

Pitzer’s correlation limitation?

Answer 4

Does not work so well for highly polar fluids (eg H2O)

Question 5

What does van der Waals EoS include terms to correct for? Its advantages and limitations?

Answer 5

• Attractive forced between molecules
• Volume occupied by gas molecules (repulsive component)
  It is simple and useful for gases that deviate moderately from ideality. But, it is cubic and results in three values obtained for the volume, thus not very accurate

Question 6

When is Dalton’s law of partial pressures not valid?

Answer 6

At high pressures

Question 7

Which is closer to real value, Amagat partial volume or Dalton partial pressure?

Answer 7

Amagat

Question 8

What is a partial molar property?

Answer 8

Thermodynamic quantity that indicates how an extensive property of a solution or mixture varies with changes in the molar composition of the mixture at constant temp and pressure
It is the partial derivative of the extensive property with respect to the amount (no of moles) of the component of interest
Every extensive property of a mixture has a corresponding molar property

Question 9

Enthalpy definition

Hess’ Law?

Answer 9

Measures the energy of a thermodynamic system. Includes energy contributions from the internal energy of a system (U) and the amount of energy required to make room for it (PV).
Hess’ law states that the change in enthalpy in a chemical reaction is independent of the pathway between the initial and final states

Question 10

How are enthalpy changes measured?

Answer 10

A calorimeter is used for calorimetry, to measure the change in enthalpy associated with a phase change or reaction at a given pressure

Question 11

What is heat capacity?

Answer 11

The ratio of the heat added to (or removed from) an object to the resulting temp change

Question 12

What is enthalpy departure?

Answer 12

In an ideal gas, enthalpy is independent of pressure, however for supercritical and superheated steam, it is a function of pressure as well. Changes in enthalpy for real gases can be determined by using generalised departure charts to account for the deviation from the ideal-gas behaviour

Question 13

What is the enthalpy departure function?

Answer 13

It calculates the difference between real and ideal gas enthalpy at given T and v (nu)

Question 14

What is the enthalpy of vaporization (latent heat)

Answer 14

The specific energy required to transform a quantity of liquid into a gas

Question 15

Value of ΔG if reaction if spontaneous (favoured)

Answer 15

Negative

If 0 then equilib

Question 16

When is a system in thermodynamic equilibrium?

Answer 16

It is in thermal equilibrium, it is in mechanical equilibrium (pressure does not change with time or space) and it is in chemical equilibrium (chemical potential does not change with time or space)

Question 17

What is the value of chemical potential when pressure approaches 0?

Answer 17

• infinity

Question 18

When does a flash evaporation occur?

Answer 18

If a saturated liquid stream undergoes a reduction in pressure (e.g by passing through a valve). In the drum, the flashed vapour and the liquid cool to the saturation temp at a low pressure establishing a VLE

Question 19

What is flash evaporation used for?

Answer 19

To separate out components multicomponent liquid. The flashed vapour has a higher proportion of the more volatile compound, whilst the less volatile component is concentrated in the remaining liquid

Question 20

Tendencies at the bubble and dew points

Answer 20

Bubble point (TB) V -> 0, F -> L, zi = xi, β -> 0
Dew point (TD) L -> 0, F -> V, zi = yi, β -> 1