Phase diagrams

How do molecules react if a change in temperature occurs

Increase in temp = increases the kinetic energy E=1/2mv² rises

How do molecules react if a change in pressure occurs

increase in pressure exerted by the surroundings forces the molecules to become closer to each other, allows intermolecular forces to operate

Variable values of ΔG

Lowest ΔG = most stable

-ΔG = energetically favourable (spontaneous)

gas to liquid - changes ΔG

Equation for changing phase and pressure

change in phase = volume of phase x change in pressure

Entropy definition

entropy is the state of disorder - the number of ways certain particles can be arranged

Increase in entropy means more moles of a compound and more ways it can be arranged

Gas entropy > liquid entropy > solid entropy

Changing phase diagram

Phase boundaries

the phase diagram is constructed by variable pressure and variable temperature

solid lines represent phase boundaries - at the boundary phases are in equilibrium

where all meet = triple point

Supercritical region beyond phases

Beyond liquid there is a region called supercritical fluid, this is a compound that solvated like a liquid but has the diffusivity of a gas

Constructing a phase diagram

We get a closed container with our sample of either gas, liquid or solid, and we measure 3 points, trying to see where the liquid turns to vapour and that is the boundary

Vapour pressure definition

the pressure of the vapour when it is in equilibrium with its condensed phase

Heat capacity of phases, and the heating curve

How to measure the heating curve, is to keep the pressure constant and increase heat

Overtime the energy thermally will change to latent heat and change the phase of the sample

Heat capacity

Cp = the heat capacity of a material at constant pressure

Supercooling and Superheating

liquid water can be supercooled below its freezing point. The kinetic stabilization doesn’t happen as there are no nucleation centres for crystals to form

Phase Rule

e.g. water

components = 1

phases = 1

so the pressure and temperature can be varied independently