Physics - gases/vapours

Question 1

Define specific heat capacity and give the units

Answer 1

The amount of heat required to raise the temperature of 1kg of a substance by 1 degree C.
Units: kJ/kg/degree C

Question 2

Define heat capacity and give the units and formula.

Answer 2

The amount of heat required to raise the temperature of an object by 1 degree C.
Units = kJ per degree C.
Formula: T = M.s
where T = heat capacity, M = mass and s = specific heat capacity of the object.

Question 3

Define Critical Temperature

Answer 3

The critical temperature is defined as the maximum temperature at which a gas can be liquefied by increasing ambient pressure. Above critical temperature the gas cannot be liquefied by increasing ambient temperature.

Question 4

What is the critical temperature for oxygen?

Answer 4

-119 degree C

Question 5

What is the critical temperature for nitrous oxide?

Answer 5

36.5 degree C

Question 6

Define critical pressure

Answer 6

The minimum pressure, at critical temperature, required to liquefy a gas

Question 7

Define critical volume

Answer 7

The volume occupied by 1 mole of gas at critical temperature and critical pressure

Question 8

What is the triple point of water?

Answer 8

The single point at which the three phases of water coexist, at a pressure of 0.006 atmospheres and 0.01 degree C.

Question 9

Define a gas (as opposed to a vapour)

Answer 9

A substance which is normally in its gaseous state at room temperature and atmospheric pressure. Its critical temperature is below room temperature and therefore it cannot exist as a liquid.

Question 10

Define vapour (as opposed to a gas)

Answer 10

A gaseous substance which is normally in liquid form at room temperature and atmospheric pressure, since its critical temperature is above room temperature. Thus a vapour is a gaseous substance which is below its critical temperature under ambient conditions.

Question 11

Define saturated vapour pressure. How does this change with temperature?
What is the boiling point?

Answer 11

Saturated vapour pressure is the pressure exerted by a vapour when in contact and equilibrium with its liquid phase.
The SVP of a liquid increases with temperature.
The boiling point of a liquid is the temperature at which the SVP becomes equal to atmospheric pressure.

Question 12

Define specific latent heat of fusion and specific latent heat of vaporisation
Give the specific latent heat of fusion and vaporisation for water at 37 degrees.
Give the specific latent heat of vaporisation for water at 100 degrees.

Answer 12

Specific latent heat of fusion: The energy required to change 1kg of substance from solid to liquid, without change in temperature. For water: 334 kJ/kg
Specific latent heat of vaporisation: the energy required to change 1 kg of substance from liquid to vapour, without change in temperature. For water at 37 degrees: 2420 kJ/kg, at 100 degrees: 2260 kJ/kg

Question 13

What is absolute humidity?
What are the units?
How does absolute humidity vary with temperature of the air?

Answer 13

the mass of water vapour present in a given volume of air.
Units are g/cubic metre or kg/cubic metre
Does not vary with temperature

Question 14

What is relative humidity?
What are the units?
How does relative humidity change with temperature?

Answer 14

Relative humidity is the ratio of the mass of water vapour in a given volume of air at a given temperature, to the mass of water required to saturate that volume at the same temperature.
It is expressed as a percentage
It decreases as temperature increases.

Question 15

How is relative humidity calculated?

Answer 15

Relative humidity = actual water vapour pressure/saturated vapour pressure

Question 16

What is Boyle’s law?

Answer 16

At a constant temperature, pressure is inversely proportional to volume

Question 17

What is Charles’ Law?

Answer 17

At a constant pressure, volume is proportional to temperature.

Question 18

What is Gay-Lussac’s law?

Answer 18

At a constant volume, pressure is proportional to temperature.

Question 19

What is the ideal gas equation?

Answer 19

PV = nRT
P is pressure
V is volume
n = number of moles of gas present
R = universal gas constant
T = temperature

Question 20

What is the universal gas constant?

Answer 20

8.32 joules per degree C

Question 21

What is Avogadro’s hypothesis?
What is the Avogadro constant?

Answer 21

Equal volumes of gases, under the same conditions of temperature and pressure, contain equal numbers of molecules.
1 mole of gas or vapour contains the same number of molecules, which is the Avogadro constant.
Avogadro constant = 6.022 x 10 ^23

Question 22

What volume is occupied by 1 mole of gas or vapour at NTP (0 degree C or 273K and 1 atmosphere)

Answer 22

22.4 Litres

Question 23

What is Dalton’s law of partial pressures?

Answer 23

if a mixture of gases is placed in a container, the pressure exerted by each gas (partial pressure) is equal to that which it would exert if it alone occupied the container.

Question 24

What is the equation for viscosity?

Answer 24

viscosity = shear stress/shear rate
units = Poises

Question 25

How does the viscosity of liquids and gases change with change in temperature?

Answer 25

Liquids generally become less viscous with increasing temperature
Gases become more viscous with increases temperature.

Question 26

What are Newtonian fluids?

Answer 26

Fluids in which viscosity is constant, regardless of the velocity gradients produced during flow.

Question 27

What is the Hagen-Poisseuille equation?

Answer 27

Flow rate, Q = ΔPπr4 / 8ηl

Question 28

What is the kinematic viscosity of a fluid?

Answer 28

The ratio of the viscosity to the density