States of matter

unit 3

What is plasma?

How does it differ from a gas (3)?

An ionised gas, consisting of free electrons and ions

• conducts electricity

• affected by magnetic fields

• requires significant energy to form under terrestrial conditions

What are liquid crystals?

How does it compare to other states of matter?

How does it react to applied fields?

Fluid with a small degree of solid-like order

• flows like a liquid but with optical properties of a solid

• typically responsible to applied fields e.g. electrical/magnetic

What is a phase transition?

A transformation of a substance from one state of matter to another, in response to changes in its environment e.g. temperature or pressure

What is fusion another word for?

Melting

What is solidification another word for?

Freezing

What is vaporisation another word for?

Boiling / evaporating

Energy in endothermic processes?

Name 3 endothermic processes

Energy absorbed to overcome IMF

• melting, vaporisation, sublimation

Energy in exothermic processes?

Name 3 exothermic processes

Energy is released as IMF form

• freezing, condensation, deposition (gas to solid)

Heating curve

What is the equation?

What does the slope represent?

What happens at a phase transition?

q=mCΔT

Slope is heat capacity

At a phase transition, temperature is constant (gradient is zero), input energy is used to overcome IMF

• there is a mixture of both phases

What systems does the Lennard-Jones Potential model not work for?

It only works for non polar systems

• more complex interactions lead to complex phase behaviour

What is on the axes of a phase diagram?

Pressure vs temperature

What is the triple point on a phase diagram?

When solid, liquid, and gas phases coexist in equilibrium

• the only set of conditions under which phases are equally stable

What is the critical temperature T_c on a phase diagram?

The highest temperature at which a substance can exist as liquid, regardless of pressure

What is the critical pressure P_c on a phase diagram?

The pressure required to liquefy a gas at the critical temperature

What is the critical point?

The highest temperature and pressure at which a liquid and gas can coexist

Supercritical fluids

• viscosity?

• density?

• solvation power?

Low viscosity of a gas, high density of a liquid

Can have good solvation power for small molecules and polymers (can be dissolved)

How to change solvent properties of supercritical fluid?

What does this enable?

By varying pressure and temperatures near the critical point

• this enables selective extraction of specific compounds

Advantages of supercritical CO₂?

• abundant / inexpensive (waste product)

• nonflammable, nontoxic

• easily removed, captured and reused

• low critical pressure and temperatures

What are the 3 assumptions the ideal gas law makes?

• gas molecules/atoms have no volume

• no IMF between molecules/atoms

• perfectly elastic collisions

What is Z, what does it represent?

The compressibility factor

For an ideal gas, Z = 1

For a real gas, Z<1 at low pressure and Z>1 at high pressure

Why does Z change for real gases with pressure?

Attractive forces dominate at low pressure

Repulsive forces dominate at high pressure

What is van der Waals equation?

a = magnitude of attractive IMF

b = effective (excluded) vol of gas molecules/atoms

What happens to van der Waals equation when V is larger?

both terms become negligible

What does n²/V² represent in van der Waals equation? How does it change with pressure (number of molecules per volume)?

Represents the probability of molecules interacting = increases with the number of molecules per volume

What happens to Gibbs free energy of two phases at a phase transition?

The Gibbs free energy is equal

What is the Clapeyron equation? What does it show?

It quantifies how pressure and temperature change along a phase boundary

• calculates slope of phase boundary

What is Clausius-Clapeyron equation? What does it apply to?

Only applies to vaporisation and sublimation

When solute is added to system of two immiscible liquids, what happens?

Distributed between two liquid phases

• depends on solubility of solute in each solvent

What is the partition coefficient, K_D?

The equilibrium distribution of the solute between two phases

• C_org is conc of solute in organic phase

• C_aq is conc of solute in aqueous phase

How to calculate mass balance of single extraction step of liquid liquid extraction (when volume is equal)?

Why are repeated extractions useful in liquid-liquid extraction?

Some material usually remains in the aqueous phase after the first extraction

• more material isolated after each extraction