Gas Laws (Module 4)

Question 1

What is the water to air density ratio?

Answer 1

• 1w: 0.0012a
  or
• 830w:1a

Question 2

What is density?

Answer 2

mass per unit volume

Question 3

What is the density of air at STP?

Answer 3

Density of Air @ STP = 1.275 kg/m3 or 0.075 lb/ft3

Question 4

What is the density of water?

Answer 4

Density of Water = 1000 kg/m3 or 62.4lb/ft3

Question 5

What is specific gravity?

Answer 5

• density compared to some reference, where the reference is taken as one
• Typically, air or water are used as references

Question 6

What is viscosity?

Answer 6

• indication of the “cohesiveness” of air
• air has very low viscosity

Question 7

What is the viscosity of air at STP?

Answer 7

Viscosity of Air @ STP = 1.8 x 10^-5 N·s/m^2 or 3.6 x 10^-7 lb·s/ft2

Question 8

What is Boyle’s law?

Answer 8

• When the temperature of a gas is constant, then the gas volume is inversely proportional to pressure
• So if pressure increases, volume decreases or if pressure decreases, volume increases

Question 9

What is Boyle’s law equation for the volume of gas?

Answer 9

• V =k/p
• p is the (absolute) pressure of the system, V is the volume of the gas, k is a constant value

Question 10

What is Charles Law?

Answer 10

When pressure is constant, the volume of a gas varies in direct proportion to absolute temperature

Question 11

What is the equation for Charles law (volume of gas)?

Answer 11

V =kT

V is the volume of the gas
T is the temperature of the gas in absolute temperature (kelvin OR rankine ONL), k is a constant value

Question 12

what is absolute temperature?

Answer 12

• Absolute temperature is the temperature of an object on a scale where 0 is taken as absolute zero
• in kelvin or rankine
• 0 is lowest, no negatives

Question 13

What is absolute zero?

Answer 13

the lowest temperature at which the system is in a state of lowest possible (minimum) energy

Question 14

What is the combined gas law?

Answer 14

The ratio between the pressure-volume constant and the temperature of a system remains constant

Question 15

What is the ideal gas law equation?

Answer 15

PV=nRT or n/v=p/RT

where P is pressure, V the volume occupied by n moles of the gas at temperature T, R is the universal gas constant

Question 16

What is the equation of density and what is it equivalent too?

Answer 16

Density= mass/volume = mols/volume

Question 17

What are the standard conditions for air (ACGIH)

Answer 17

• Temp: 70 f
• pressure 29.92 inHg or 14.7 psi or 1 atm
• RH: 0

Question 18

What are some non-standard conditions?

Answer 18

• Changes in P and T cause density to change as well (due to volume change - mass is still constant)
• For small changes, error in density may be negligible
• Rule of thumb to apply correction if more than 5-10% change in density occurs
• If the airstream temperature is < 20 °F or
  > 120 °F, density corrections are appropr

Question 19

Do you have to worry about density variations in ventilation situations?

Answer 19

Usually no, pressure differences in a moving air system are typically less than about 5% of atmospheric and temp below about 100 °F