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