Flashcards in Science for CE - Physical Chemistry 1 Deck (24)

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1

## What's a mole?

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

2

## How is force calculated between 2 charged particles?

###
πΉπ = π1π2 / 4ππ0π2

Fc: attractive force between charges

Ξ΅0: vacuum permittivity (8.85 Γ 10β12πΆ2π½β1πβ1)

q1, q2: point charges

r: distance between charged points

3

## What are dipole moments measured in?

###
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 CΒ·m (1 coulomb-meter).

4

## What's the Leonard-Jones potential?

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

The repulsive (rβ12) term, approximates Pauli repulsion at short ranges due to overlapping electron orbitals.

The attractive (rβ6) term, describes attraction at long ranges (van der Waals and/or London dispersion forces).

5

## What are cations and anions?

###
Cation - positive ions

Anion - negative ions

6

## Whatβs an ideal gas?

###
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.

7

## Whatβs Boyleβs law?

### pV = constant

8

## Whatβs Charlesβ law?

### V/T = constant

9

## What is Gay-Lussacβs law?

### P/T = constant

10

## What is Avogadroβs principle?

###
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)

11

## What is Dalton's law of partial pressures?

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

ππ‘ππ‘ = π = ππ΄ + ππ΅+β¦

12

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

###
Ptot = PA + PB

π₯π΄+π₯π΅ = 1

π = ππ΄+ππ΅

ππ΄ = ππ₯π΄

ππ΅ = ππ₯π΅

(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)

13

## What's the kinetic model of gases?

###
Theoretical model of the action of molecules, assuming:

- molecules have mass m

- the mean free path, π, is much larger than the diameter of the molecule, d. (π>>d)

- only elastic collisions. p is conserved

14

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

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

Force is equal to the rate of change of momentum (Newton's second law).

F = ma = Ξππ£/Ξπ‘

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

Therefore overall:

p = mNv^2/3V

15

## How is rms (root mean square) calculated?

###
π£,πππ = (ππ)^1/2 =

(3π
π/πππ΄)^1/2

Molecular mass M = mNA

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

16

## What is mean free path?

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

17

## How is average kinetic energy per molecule, ππ, calculated?

###
ππ = 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.

18

## How is kinetic energy per mol calculated?

### Ek = (ππ)ππ΄ = 3RT/2

19

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

###
π(π£) = 4π(π/2ππ
π)^3/2 * π£^2

*π^β(ππ£^2/2π
π)

20

## What does Maxwell-Boltzmann distribution show?

###
Plot of relative number of molecules against speed.

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

21

## How is the fraction of molecules that have velocities in the range π£ to π£ + ππ£ determined?

### It is proportional to dv.

22

## What's the Boltzmann factor?

###
e^-(Mv^2/2RT)

= e^-(π/kT)

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

23

## What is the Principle of Corresponding States?

###
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, ππ have the same reduced

volume, ππ.

24