Modelling a gas

Question 1

Mole

Answer 1

A quantity of substance with the same number of particles as 12 grams of carbon -12.

Question 2

Avogadro’s constant

Answer 2

6.02 x 10²³

Question 3

Formula for no. of particles

Answer 3

n = N / N_A
no. of moles= No. of particles/Avogadro’s no.

Question 4

Formula for mass, molecular mass and moles

Answer 4

n = m/μ
no. of moles = mass/ molecular mass

Question 5

Pressure definition

Answer 5

Force acting perpendicularly per unit area

Question 6

Pressure in solids when force is at an angle

Answer 6

P = F cos θ /A

Question 7

Pressure in liquids

Answer 7

P = heg
Pressure = height x density x gravity

Question 8

Properties of an ideal gas

Answer 8

• Molecules are point particles, each with negligible volume
• Molecules obey the laws of mechanics
• No forces between molecules except during collisions
• Duration of collisions is negligible compared to time between collisions
• Collisions between molecules and with the walls of the container are perfectly elastic
• Molecules move randomly with a range of speeds
• Do not change state

Question 9

Properties of a real gas that prevent them from being ideal gases

Answer 9

• Forces between molecules
• Molecules have definite volume
• They condense before zero
• Condense at high pressure and low temperature

Question 10

Pressure-volume (Boyle’s) law

Answer 10

For a gas with contsant temperature and mass, pressure is inversely proportional to volume

Question 11

Pressure-volume law equation

Answer 11

p=k/V
p₁ V₁ = p₂ V₂

Question 12

Volume-temperature (Charle’s) law

Answer 12

The volume of a fixed mass of gas at constant pressure is directly proportional to its absolute temperature

Question 13

Volume-temperaure law equation

Answer 13

V = kT
V₁ / T₁ = V₂ / T₂

Question 14

What is absolute zero?

Answer 14

0 Kelvin. When particles are not moving

Question 15

Pressure- temperature (Gay-Lussac’s) law

Answer 15

Pressure of a fixed mass of gas, at constant volume, is direcly proportional to absolute temperature

Question 16

Pressure-temperature law equation

Answer 16

P = kT
p₁ / T₁ = p₂ / T₂

Question 17

Isobar

Answer 17

Line joining points at the same pressure

Question 18

Isothermal

Answer 18

Line joining points at the same temperature

Question 19

Combined gas law

Answer 19

p₁ V₁ / T₁ = p₂ V₂ / T₂

Question 20

Equation of state of an ideal gas

Answer 20

pV = nRT

p = pressure (pa)
V= volume (m³)
n = no. of moles
R = 8.31
T = Temperature (K)

Question 21

Value of R (universal gas constant)

Answer 21

R = 8.31 J/Kmol

Question 22

Kinetic energy of 1 molecule of gas (2 equations)

Answer 22

E_K = 1/2 mc²
E_K = 3/2 K_B T

c = root mean square speed (r.m.s)
c² = mean square speed
K_B = R/N_A (Boltzmann’s constant)

Question 23

Pressure of a gas

Answer 23

p = 1/3 ec²

e = density (kg/m³)

Question 24

Internal energy(U)

Answer 24

U = 3/2 nRT