Science for CE - Physical Chemistry 1

Question 1

What’s a mole?

Answer 1

The amount of substance which contains as many elementary entities (atoms or molecules) as there are atoms in 0.012 kg of 12C.

Question 2

How is force calculated between 2 charged particles?

Answer 2

𝐹𝑐 = 𝑞1𝑞2 / 4𝜋𝜀0𝑟2

Fc: attractive force between charges

ε0: vacuum permittivity (8.85 × 10−12𝐶2𝐽−1𝑚−1)

q1, q2: point charges

r: distance between charged points

Question 3

What are dipole moments measured in?

Answer 3

Debye, D

A single negative charge (an electron) separated from a single positive charge (a proton) has a dipole moment of 1D = 3.336x10-30 C·m (1 coulomb-meter).

Question 4

What’s the Leonard-Jones potential?

Answer 4

An approximation of the interaction between a pair of neutral atoms or molecules.

The repulsive (r−12) term, approximates Pauli repulsion at short ranges due to overlapping electron orbitals.
The attractive (r−6) term, describes attraction at long ranges (van der Waals and/or London dispersion forces).

Question 5

What are cations and anions?

Answer 5

Cation - positive ions

Anion - negative ions

Question 6

What’s an ideal gas?

Answer 6

A gas where each molecule is a point sized object, their only interactions being elastic collisions (all energy is conserved).

Their paths are unaffected by intermolecular forces.

Question 7

What’s Boyle’s law?

Answer 7

pV = constant

Question 8

What’s Charles’ law?

Answer 8

V/T = constant

Question 9

What is Gay-Lussac’s law?

Answer 9

P/T = constant

Question 10

What is Avogadro’s principle?

Answer 10

V/n = constant (for constant p and T).

The volume of 1 mole of ANY gas at STP (273.15K, 1atm) is 22.4 (litres per mole)

Question 11

What is Dalton’s law of partial pressures?

Answer 11

The pressure P, exerted by a mixture of ideal gases is the sum of the partial pressures of the gases.

𝑃𝑡𝑜𝑡 = 𝑃 = 𝑃𝐴 + 𝑃𝐵+…

Question 12

How does Dalton’s law of partial pressures apply to binary mixtures of 2 gases, A and B?

Answer 12

Ptot = PA + PB

𝑥𝐴+𝑥𝐵 = 1
𝑛 = 𝑛𝐴+𝑛𝐵
𝑃𝐴 = 𝑃𝑥𝐴
𝑃𝐵 = 𝑃𝑥𝐵
(x is mole fraction)

Total P remains constant

When the mol fraction of B, approaches 1, then the mol fraction of A becomes 0 (and vice versa)

Question 13

What’s the kinetic model of gases?

Answer 13

Theoretical model of the action of molecules, assuming:

• molecules have mass m
• the mean free path, 𝜆, is much larger than the diameter of the molecule, d. (𝜆»d)
• only elastic collisions. p is conserved

Question 14

How is pressure exerted on a surface by a molecule calculated?

Answer 14

Pressure = (force of collisions/area) * number of collisions

Force is equal to the rate of change of momentum (Newton’s second law).
F = ma = Δ𝑚𝑣/Δ𝑡

Number of collisions is calculated by 1/2(N/V)(vxΔtA)

Therefore overall:
p = mNv^2/3V

Question 15

How is rms (root mean square) calculated?

Answer 15

𝑣,𝑟𝑚𝑠 = (𝒗𝟐)^1/2 =
(3𝑅𝑇/𝑚𝑁𝐴)^1/2

Molecular mass M = mNA
Therefore, v,rms = (3RT/M)^1/2

Question 16

What is mean free path?

Answer 16

The average distance travelled by a gas molecule or other particle between collisions with other particles.

Question 17

How is average kinetic energy per molecule, 𝜀𝑘, calculated?

Answer 17

𝜀𝑘 = 3RT/2NA
= 3kT/2

Where k (kB) is the Boltzmann’s constant, 1.38066*10^-23 J/K

Multiply by number of molecules for kinetic energy per mol = 3RT/2.

Question 18

How is kinetic energy per mol calculated?

Answer 18

Ek = (𝜀𝑘)𝑁𝐴 = 3RT/2

Question 19

How is the distribution of velocities of a gas at temperature, T, given?

Answer 19

𝑓(𝑣) = 4𝜋(𝑀/2𝜋𝑅𝑇)^3/2 * 𝑣^2

*𝑒^−(𝑀𝑣^2/2𝑅𝑇)

Question 20

What does Maxwell-Boltzmann distribution show?

Answer 20

Plot of relative number of molecules against speed.

Area under curve is equal to the total number of molecules.

Question 21

How is the fraction of molecules that have velocities in the range 𝑣 to 𝑣 + 𝑑𝑣 determined?

Answer 21

It is proportional to dv.

Question 22

What’s the Boltzmann factor?

Answer 22

e^-(Mv^2/2RT)

= e^-(𝜀/kT)

which is the fraction of molecules of a particular energy level.

Question 23

What is the Principle of Corresponding States?

Answer 23

Substances behave alike at the same reduced states. Substances at the same reduced states are at corresponding states.

This means that:
Fluids at the same reduced pressures, Pr and temperatures, 𝑇𝑟 have the same reduced
volume, 𝑉𝑟.

Question 24

What’s Boyle’s temperature?

Answer 24

There is a temperature limit at which a non ideal gas behaves most like an ideal gas.

Non ideal bases behave similar to ideal gases.
The 2nd burial coefficient is 0 (compression factor is most ideal)