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Flashcards in THERMO3 Deck (33):
1

The Ideal Gas Equation

PV = nRT

2

Van dear Waal's Equation of State
Definition

The ideal Gas equation adapted for real gases

3

Van dear Waal's Equation of State
Equation

(P + an²/V²)*(V - bn) = nRT

P = pressure
V = volume
n = number of Moles
R = molar gas constant
T = temperature
b = actual volume of one mole of gas molecules
a = pressure per unit volume, depends on the gas and is small for inert gases

4

Van dear Waal's Equation of State
Explanation

(P + an²/V²)*(V - bn) = nRT
-V is lower than measured since the Gas molecules themselves take up volume, the free volume for the molecules to move into is the volume of the container, V minus the volume of the molecules, bn
-P is her than measured, as a molecule approaches the wall of the container it is attracted back by the other molecules with a force proportional to the density, n/V. But the number of molecules hitting the wall is also proportional to density thus the attractive force is actually proportional to (n/V)²

5

Density
Molar Equation

M / b

M = molar mass
b = molar volume

6

Isotherm
Definition

Lines of constant temperature

7

Critical Isotherm

The first isotherm where P isn't inversely proportional to V

8

Critical Temperature

The temperature of the critical isotherm

9

What is the critical temperature for water?

Tc = 647K

10

Saturated Vapour

A Vapour in equilibrium with its liquid

11

What happens when the volume of a Vapour is decreased?

1. Pressure increases until a saturated vapour is formed and a maximum pressure, the saturation vapour pressure is reached
2. Some vapour becomes liquid, the remaining vapour stays at saturation vapour pressure
3. Eventually all of the vapour becomes liquid
4. At this point pressure rapidly increases with even a small further decrease in volume

12

Cryogen
Definition

Gas that becomes liquified at low temperatures

13

Uses of Cryogens

Liquid Helium - cools superconducting magnets in MRI
Liquid Argon -

14

Melting

Fusion, solid -> liquid

15

Boiling

Vaporisation, liquid -> vapour

16

Sublimation

Solid -> vapour

17

Phase Diagrams
P & T

-the line TC shows vapour pressure with temperature
-moving along T towards C, liquid pressure decreases and vapour pressure increases
-at C, liquid and vapour are indistinguishable

18

Triple Point

-at triple point solid, liquid and vapour are in equilibrium

19

Gas vs. Vapour

-a vapour can be liquefied when compressed
-a gas when compressed will follow the relationship of P inversely proportional to V

20

Phase Diagram for Water

-water is unusual in that TB has a negative gradient
-melting temperature decreases with increasing pressure

21

Normal Boiling Point

Temperature at which vapour pressure is 1atm

22

Humidity

Relative Humidity =
PP of H2O/saturation vapour Pressure X 100%

23

Heat Capacity Equation

Q = CΔT

Q = heat added to system
C = heat capacity
ΔT = change in temperature

24

Specific Heat Capacity Equation

Q = mcΔT

Q = heat added to the system
m = mass of the sample
c = specific heat capacity of the material
ΔT = change in temperature

25

Specific Heat Capacity
Definition

Heat needed to raise the temperature of 1kg by 1K

26

Molar Specific Heat
Definition

Heat needed to raise the temperature of 1mole by 1K

27

Molar Specific Heat Equation

Q = nc'ΔT

c' = Mc

Q = heat added to the system
n = number of Moles
c' = molar specific heat
ΔT = change in temperature
M = molar mass
c = specific heat capacity

28

Latent Heat
Definition

Heat needed to change the phase of 1kg

29

Latent Heat
Equation

Q = mL

Q = heat added to the system
m = mass of sample
L = latent heat

30

Lf
Definition

Latent Heat of Fusion
The heat needed to change 1kg of solid into liquid

31

Lv
Definition

Latent Heat of Vaporisation
The heat needed to change 1kg of liquid into vapour

32

What happens to temperature during phase change?

Temperature remains constant during changes of phase

33

How does the specific heat capacity and latent heat water compare to other substances?

Water has unusually high values of latent heat and specific heat capacity