6- Liquids and Solids

small repeating units that make up crystalline solids stacked over and over

unit cell

How many atoms are in a simple cubic unit cell?

1

-atoms at corners of the unit cell comprise 1 whole atom

How many atoms are in a body-centered cubic unit cell?

2

-atoms at the corners of the unit cell comprise 1 whole atom, plus the whole atom in the middle of the unit cell

How many atoms are in a face-centered cubic unit cell?

4

-atoms at the corners of the unit cell comprise 1 whole atom, plus the 6 atoms that exist halfway on each face comprise 3 whole atoms

liquid to gas

vaporization

gas to liquid

condensation

liquid to solid

cystallization

solid to liquid

fusion (melting)

solid to gas

sublimation

gas to solid

deposition

what are the endothermic phase changes?

endothermic (consume heat)

endothermic = +delta H (enthalpy)

endothermic = +delta S (entropy; more disorder)

sublimation, fusion (melting), or vaporization (boiling)

what are the exothermic phase changes?

exothermic (release heat)

exothermic = -delta H (enthalpy)

exothermic = -delta S (entropy, less disorder)

condensation, deposition, crystallization

when vapor pressure = external/atmospheric pressure

boiling point

a graphical way to show the pressures and temperatures at which a substance will exist as a solid, a liquid, or a gas, or in some kind of equilibrium in between two or more of these states

phase diagram (looks like a butt)

-outside of butt: gas

-left cheek: solid

-right cheek: liquid

triple point is where all these lines converge and it's the pressure/temperature combination at which all three phases exist at the same time, in equilibrium with each other

what do the axes in a phase diagram represent?

x axis: temperature

y axis: pressure

what is a critical point in a phase diagram?

the pressure/temperature combination at which liquids and gases are indistinguishable

(the liquid-gas line no longer exists here)