THERMO3 Flashcards
The Ideal Gas Equation
PV = nRT
Van dear Waal’s Equation of State
Definition
The ideal Gas equation adapted for real gases
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
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
Density
Molar Equation
M / b
M = molar mass b = molar volume
Isotherm
Definition
Lines of constant temperature
Critical Isotherm
The first isotherm where P isn’t inversely proportional to V
Critical Temperature
The temperature of the critical isotherm
What is the critical temperature for water?
Tc = 647K
Saturated Vapour
A Vapour in equilibrium with its liquid
What happens when the volume of a Vapour is decreased?
- Pressure increases until a saturated vapour is formed and a maximum pressure, the saturation vapour pressure is reached
- Some vapour becomes liquid, the remaining vapour stays at saturation vapour pressure
- Eventually all of the vapour becomes liquid
- At this point pressure rapidly increases with even a small further decrease in volume
Cryogen
Definition
Gas that becomes liquified at low temperatures
Uses of Cryogens
Liquid Helium - cools superconducting magnets in MRI
Liquid Argon -
Melting
Fusion, solid -> liquid
Boiling
Vaporisation, liquid -> vapour
Sublimation
Solid -> vapour
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
Triple Point
-at triple point solid, liquid and vapour are in equilibrium
Gas vs. Vapour
- a vapour can be liquefied when compressed
- a gas when compressed will follow the relationship of P inversely proportional to V
Phase Diagram for Water
- water is unusual in that TB has a negative gradient
- melting temperature decreases with increasing pressure
Normal Boiling Point
Temperature at which vapour pressure is 1atm
Humidity
Relative Humidity =
PP of H2O/saturation vapour Pressure X 100%
Heat Capacity Equation
Q = CΔT
Q = heat added to system C = heat capacity ΔT = change in temperature
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
Specific Heat Capacity
Definition
Heat needed to raise the temperature of 1kg by 1K
Molar Specific Heat
Definition
Heat needed to raise the temperature of 1mole by 1K
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
Latent Heat
Definition
Heat needed to change the phase of 1kg
Latent Heat
Equation
Q = mL
Q = heat added to the system m = mass of sample L = latent heat
Lf
Definition
Latent Heat of Fusion
The heat needed to change 1kg of solid into liquid
Lv
Definition
Latent Heat of Vaporisation
The heat needed to change 1kg of liquid into vapour
What happens to temperature during phase change?
Temperature remains constant during changes of phase
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
