General

Question 1

What is 1 bar in Pascal?

Answer 1

1 bar = 10⁵ Pa

Question 2

What is 1 Pa in bar?

Answer 2

1 Pa = 1 Pa x [1 bar / 100000 Pa]

= 1/100000 bar

Question 3

What is the boundary of a system?

Answer 3

The real or imaginary surface that separates the system from its surroundings. The boundary of a system can be fixed or movable.

Question 4

What is a cycle in Thermodynamics?

Answer 4

A cycle is a process, or series of processes, that allows a system to undergo state changes and returns the system to the initial state at the end of the process. That is, for a cycle the initial and final states are identical.

Question 5

What is the molar mass of Argon?

Answer 5

The molar mass of Argon is 40 u (g/mole, kg/kmole) [0 d.p.]

Question 6

What is molar mass?

Answer 6

Molar mass is the mass of a given substance per mole of that substance (g/mol, kg/kmol), where 1 mole is 6.02 x 10²³ atoms of that substance.

m^~= m/n

Question 7

What is the molar mass of Nitrogen in air?

Answer 7

The molar mass of Nitrogen is 28 u (g/mol, kg/mol) [0 d.p.]

As an individual atom it has an atomic mass of approx 14 kg/kmol, but it is diatomic in air.

Question 8

What is the molar mass of Oxygen in air?

Answer 8

The molar mass of Oxygen is 32 u (g/mol, kg/kmol) [0 d.p.]

As an individual atom it has an atomic mass of approx 16 kg/kmol, but it is diatomic in air.

Question 9

What is the molar mass of Hydrogen in air?

Answer 9

The molar mass of Hydrogen in air is 2 u (g/mol, kg/kmol) [0 d.p.]

As an individual atom it has an atomic mass of approx 1 kg/kmol, but it is diatomic in air.

Question 10

What is the molar mass of air?

Answer 10

The molar mass of air is 29 u (g/mol, kg/kmol) [0 d.p.]

Question 11

What is the molar mass of steam?

Answer 11

The molar mass of steam is 18 u (g/mol, kg/kmol) [0 d.p.]

Question 12

What is the Universal Gas Constant?

Answer 12

The Universal Gas Constant, R~, is 8.314 kJ kmol^-1 K^-1

Question 13

How do you find the mass of substance from the number of molecules?

Answer 13

Given that n = m/m^~

mass is given by multiplying the number of molcules by the molar mass of the substance:

m = nm^~

Question 14

How do you find the number of molecules of a substance from the mass of substance?

Answer 14

Given that m = nm^~

The number of molecules is given by dividing the mass by the molar mass of the substance:

n = m/m^~

Question 15

How can you work out the specific gas constant for a substance from the universal gas constant?

Answer 15

Given that R^~ = Rm^~

The specific gas constant of a substance can be found dividing the universal gas constant by the molar mass of the substance:

R^~/m^~ = R (kJ kg^-1 K^-1)

Question 16

How can you work out the universal gas constant from the specific gas constant of a substance?

Answer 16

Given that R = R^~/m^~

The universal gas constant can be determined by multiplying the specific gas constant of a substance by the molar mass of that substance:

R^~ = Rm^~

Units (J mol^-1 K^-1 or kJ kmol^-1 K^-1)

Question 17

Briefly discuss Heat Capacity.

Answer 17

The heat capacity, sometimes called thermal capacity, (C) of a body is defined as being the heat required to produce a temperature rise of one unit.

It follow that if the temperature of a body whose heat capacity is C rises by ∆T when an amount of heat ∆Q is added to it, then:

∆Q = C∆T

Unit of heat capacity = J K ^{- 1}

Question 18

Briefly discuss specific heat capacity.

Answer 18

The term specific heat capacity refers to the heat capacity of unit mass of a given substance.

It follows that if the temperature of a body of mass m and specific heat capacity c rises by ∆T when an amount of heat ∆Q is added then:

∆Q = mc∆T

Unit of specific heat capacity = J kg ^{- 1} K ^{- 1}

Question 19

Briefly discuss the relationship between heat capacity C, specific heat capacity c, and mass m.

Answer 19

Heat capacity C is a measure of the heat energy required to affect a change in temperature of one unit for a given mass of a given substance.

Specific heat capacity c is a measure of the heat energy required to affect a change in temperature of one unit per unit mass of a given substance.

Therefore:

C = mc

Question 20

What is Boyle’s Law?

Answer 20

Boyle’s Law is one of the gas laws.

It states “For a fixed mass of gas (ideal) at constant temperature, the product of pressure and volume is constant.”

This can be expressed as follows:

pV = a constant at constant T

Question 21

What is Charles’ Law?

Answer 21

Charles’ Law is one of the gas laws.

It states “For a fixed mass of gas (ideal) at constant pressure, the volume is directly proportional to the temperature measured in kelvins.”

This can be expressed as follows:

V / T = a constant at constant p

Question 22

What is the Pressure Law?

Answer 22

The Pressure Law is one of the gas laws.

It states “For a fixed mass of gas (ideal) at constant volume, the pressure is directly proportional to the temperature in kelvins.”

This can be expressed as follows:

p / T = a constant at constant V

Question 23

What is the Ideal Gas Law?

Answer 23

The behaviour of an ideal gas can be accounted for with the following equation:

pV = nR^~T

Where:

p = the pressure of the gas (Nm ^{- 2})

V = the volume of the gas (m³)

n = the number of moles of gas (mol)

R^~ = the universal gas constant (8.314 J mol ^{- 1} K ^{- 1}

or kJ kmol ^{- 1} K ^{- 1})

T = the temperature of the gas in kelvins

or

pV = mRT

Where:

p = the pressure of the gas (Nm ^{- 2})

V = the volume of the gas (m³)

m = the mass of the gas (kg)

R = the specific gas constant (kJ kg ^{- 1} K ^{- 1})

T = the temperature of the gas in kelvins

Question 24

What do these graphs represent?

Answer 24

These graphs are representations of Boyle’s Law i.e.

pV = constant at constant temperature

Where p is the pressure and V is the volume of a fixed amount of gas at constant temperature.

Each curve is for a specific temperature. Each of the curves is referred to as an isothermal, because each curve is a constant temperature.

For a given curve, any pair of measurements, p₁ and V₁, is related to any other pair of measurements, p₂ and V₂, by Boyle’s law equation in the form:

p₁V₁ = p₂V₂

This holds true for an ideal gas.

Question 25

What is specific gravity, how is it determined, and what is the unit of specific gravity?

Answer 25

Specific Gravity - SG - is a dimensionless unit defined as the ratio of the density of a given substance to the density of water (at a specified temperature), and can be expressed as

SG = ρ_substance / ρ_H2O

where:

SG = Specific Gravity of the substance

ρ_substance = density of the fluid or substance (kg/m3)

ρ_H2O = density of water (normally at temperature 4 ºC) (kg/m3)

It is common to use the density of water at 4 ºC (39 ºF) as a reference since water at this point has its highest density of 1000 kg/m3 or 62.4 lb/ft3.

Specific Gravity - SG - is dimensionless and has the same value in the SI system and the imperial English system (BG). Water is normally also used as reference when calculating the specific gravity for solids.