Lecture 1

Question 1

state

Answer 1

• the state in which a substance exists depends on the competition or balance between intermolecular forces and thermal energy

Question 2

particles of a substance

Answer 2

enough energy to completely overcome intermolecular interactions, particles can separate from each other and move about randomly in space

Question 3

gases

Answer 3

greatest disorder, no definite shape, no definite volume

Question 4

solids

Answer 4

ordered

Question 5

state of gases

Answer 5

• no definite shape
• no definite volume
• particles move in a random motion with little or no attraction to each other
• highly compressible

Question 6

pressure

Answer 6

• pressure of a gas is due to collisions of the molecules with the walls of the container
• the greater the force acting on a given area, the greater the pressure

pressure formula: P = F/A

Question 7

pressure unit

Answer 7

1 Pa = 1Nm-2
1 Pa = 1kg m-1s-2
1 atm = 1.01325 x 105 Pa
1 bar = 105 Pa

Question 8

mechanical equilibrium

for pressure

Answer 8

• when a region of high pressure is separated by a movable wall, the wall will be pushed into one region (the higher pressure side will compress the low pressure side)
• mechanical equilibrium = pressures are identical, the wall will not move (pressure of both the gases is equalised)

Question 9

thermal equilibrium

for temperature

Answer 9

• energy flows as heat from a region at a higher temperature to a region of low temperature
• if the two regions have identical temperatures, there is no net transfer of energy heat (thermal equilibrium)

Question 10

zeroth law of thermodynamics

Answer 10

if A is in thermal equilibrium with B, and A is in thermal equilibrium with C, C and B are also in thermal equilibrium

Question 11

gas law

Answer 11

deals with how gases behave in respect to pressure, volume, temperature and amount

Question 12

gas law and pressure

Answer 12

at constant pressure, the volume of a fixed mass of gas is proportional to its temperature

Question 13

charles’ law

Answer 13

V/T = constant

Question 14

Boyles’ Law

Answer 14

provided temperature is kept constant, the volume of a fixed mass of gas is inversely proportional to its pressure (isothermal)

pV = constant

Question 15

ideal gas equation

Answer 15

pV = nRT

Question 16

terms of ideal gas law

Answer 16

• pressure = Pa
• volume = m3
• temperature = kelvin
• n = number of moles
• R = gas constant (8.31441 J K-1mol-1

Question 17

modified equation

Answer 17

P1V1/T1 = P2V2/T2

Question 18

deviations

Answer 18

• no real gas obeys the law completely
• they show deviations
• ideal gas law makes assumptions
• 1. no intermolecular forces in the gas and the gas molecules have no volume

Question 19

low pressure

Answer 19

behaviour of a gas is ideal

Question 20

van der Waals equation

Answer 20

(p + a.n2/V2)(V-n.b) = n.R.T

Question 21

van der Waals equation terms

Answer 21

p = pressure
v = volume
T = temperature
R = gas constant
a,b = specific constant for each gas

Question 22

limitations of van der Waals

Answer 22

gases tend to liquify under high pressures (at low temperatures) that is why deviations are seen

Question 23

critical point

Answer 23

• set of conditions under which a liquid and its vapour become identical
• at this critical point, we can define a critical temperature, critical pressure and critical volume
• we can introduce dimensionless, reduced variables of a gas by diving the actual variable by the corresponding critical constant.

Question 24

critical constant equation

Answer 24

Pr = P/Pc
Vr = V/Vc
Tr = T/Tc

Question 25

principles of corresponding states

Answer 25

• the reduced pressure of a van der Waals gas is:
• in the reduced equation, the coefficients a and b, which differ from gas to gas, have disappeared
• real gases at the same reduced volume and reduced temperature exert the same reduced pressure

Question 26

principle of corresponding states equation

Answer 26

Pr = (8Tr/ 3Vr-1) - (3/Vr^2)

Question 27

system

Answer 27

part of the world in which we have a special interest

Question 28

surroundings

Answer 28

region outside the system and where we make our measurements

Question 29

open system

Answer 29

can exchange mass and energy, usually in the form of heat with its surroundings

Question 30

closed systems

Answer 30

which allows the transfer of energy (heat) but not mass

Question 31

isolated system

Answer 31

which doesn’t allow the transfer of either mass or energy