Mixtures of Gases, Vapors, and Liquids

Question 1

Mass Fraction (Gravimetric or Weight Fraction)

Answer 1

The mass fraction is the ratio of the component’s mass to the total mass of the mixture. The sum of all the mass fractions is always equal to one.

Question 2

Mole Fraction

Answer 2

The mole fraction is the ratio of the number of moles of that substance to the total number of moles of all the substances in the mixture. The mole fraction of a mixture of non reacting ideal gases is equal to the partial pressure ratio and volumetric fraction. The sum of all the mole fractions is always equal to one.

Question 3

Molecular Weight

Answer 3

The molecular weight is the mass per mole of a component. It is used to convert mass fraction to mole fraction and vice versa.

Question 4

Partial Pressure

Answer 4

The pressure a gas component would alone exert in the total volume at the temperature of a mixture of non reacting gases. (Ideal Gas Law)

Question 5

Dalton’s Law

Answer 5

The total pressure of a gas mixture is the sum of the partial pressures.

Question 6

Partial Volume

Answer 6

The volume a gas component would alone occupy, at the temperature and pressure of a mixture of non reacting gases. (Ideal Gas Law)

Question 7

Amagat’s Law

Answer 7

The total volume of a mixture of non reacting gases is equal to the sum of the partial volumes.

Question 8

Ideal Gas Mixtures

Answer 8

For mixtures of non reacting ideal gases, the mole fraction, partial pressure ratio, and volumetric fraction are the same.

Question 9

Gibbs Theorem

Answer 9

States that the total property of a mixture of ideal gases is the sum of the properties that the individual gases would have if each occupied the total mixture volume alone at the same temperature. The total entropy requires the mixing of components to be isentropic and each components entropy must be evaluated at the temperature of the mixture and its partial pressure.

Question 10

Henry’s Law

Answer 10

States that the partial pressure of a slightly soluble gas above a liquid is proportional to the amount (mole fraction) of the gas dissolved within the liquid. This law applies separately to each gas to which the liquid is exposed, as if each gas were present alone. It is important to recognize that (h) is Henry’s Law constant with units of pressure, (x) is the mole fraction of the gas solute in the liquid solvent, while (y) is the mole fraction of the gas solute in the gas mixture above the liquid.

Question 11

Vapor Pressure

Answer 11

The vapor pressure is the pressure exerted by the solvent’s vapor molecules when they are in equilibrium with the liquid. Vapor pressure increases with increasing temperature.

Question 12

Raoult’s Law

Answer 12

According to Raoult’s Law, the partial pressure of a solution component will increase with increasing temperature and with increasing mole fraction of that component in the solution. This law applies to each of the substances in the solution.

Question 13

Psychometrics

Answer 13

Psychometrics is the study of the properties and behavior of atmospheric air.

Question 14

Atmospheric Air

Answer 14

Atmospheric air contains small amounts of moisture and can be considered to be a mixture of two ideal gases, dry air and water vapor. All of the thermodynamic rules relating to the behavior of non reacting gas mixtures apply to atmospheric air.

Question 15

Total Atmospheric Pressure

Answer 15

The total atmospheric pressure is equal to the sum of the dry air partial pressure and water vapor partial pressure.

Question 16

Dry Bulb Temperature

Answer 16

The temperature that a regular thermometer measures if exposed to air.

Question 17

Wet Bulb Temperature

Answer 17

The temperature of air that has gone through an adiabatic saturation process. It is measured with a thermometer that is covered with a water saturated cotton wick.

Question 18

Dew Point Temperature

Answer 18

This is the dry bulb temperature at which water starts to condense when moist air is cooled in a isobaric process. The dew point temperature is equal to the saturation temperature for the partial pressure of the vapor.

Question 19

Saturation Pressure

Answer 19

For every temperature, there is a unique equilibrium vapor pressure of water called the saturation pressure. If the vapor pressure equals the saturation pressure, the air is said to be saturated.

Question 20

Saturated Air

Answer 20

Saturated air is a mixture of dry air and water vapor at the saturation pressure. When the air is saturated, all three temperatures are equal.

Question 21

Unsaturated Air

Answer 21

Unsaturated air is a mixture of dry air and superheated water vapor. When the air is unsaturated, the dew point temperature is lower than the wet bulb temperature, and the wet bulb temperature is lower than the dry bulb temperature.

Question 22

Specific Humidity (Humidity Ratio)

Answer 22

The humidity ratio is equal to the mass ratio of water vapor to dry air and it specifies the amount of water in atmospheric air. The partial pressure can also be used to obtain the humidity ratio.

Question 23

Relative Humidity

Answer 23

The relative humidity is the partial pressure of the water vapor divided by the saturation pressure at the dry bulb temperature.

Question 24

Psychometric Chart

Answer 24

Psychometric chart is used by specifying the values of any two parameters on intersecting scales. Once the state has been located on the chart, all other properties can be read directly.

Question 25

Enthalpy of Dry Air

Answer 25

Enthalpy of an air vapor mixture is the sum of the enthalpy of dry air plus the product of the enthalpy of the water vapor and humidity ratio. This computes the enthalpy per pound of dry air. In psychometrics, the basis for the total enthalpy of air (an air water vapor mixture) is the mass of the dry air only not the total air mass.