Chem 30A
Dr Schaleger
Chapters 8 – 9
Useful Relationships
Laney College
Spring 2014
Chapter 8. Solids, liquids, gases
Equilibria: At equilibrium, ΔG = 0 = ΔH – TΔS
Gases: mixtures of gases are homogeneous. The particles of a homogeneous mixtures are evenly
distributed. A heterogeneous mixture consists of two or more phases.
PV = nRT and since n (number of moles) = m (mass) divided by MW (molar mass), PV = mRT/MW.
P1V1/T1 = P2V2/T2 (combined Charles, Boyles and Gay-Lussac’s Laws)
Dalton’s law of partial pressures: p(total) = p1 + p2 + p3 + p4…….Where p1, etc, is the partial pressure
of a particular gas.
Equilibria of melting and boiling:
For any substance, S, the following are true: S(s) = S(l); ΔH(fusion) is positive (requires energy),
ΔS(fusion) is positive (less order).
S(l) = S(g); ΔH(vap) is positive, ΔS(vap) is positive.
Chapter 9. Solutions.
Concentration units: v/v, m/v, m/m, ppm, ppb, Molarity, Normality (chapter 10).
Molarity = moles per liter of solution.
Dilution problems: M1V1 = M2V2.
Solubility of slightly soluble salts, for example, BaSO4:
The solubility product expression is given by Ksp = [Ba2+][SO42-] where Ksp is a constant
dependent on temperature. A saturated solution of barium sulfate consists of two phases, (1) solid barium
sulfate; and (2) an aqueous solution of barium and sulfate ions.
Henry’s Law governs the solubility of gases in, say, water and other liquids. Increasing T always results
in decreasing concentration. Gases are more soluble in liquids at lower temperatures. Increasing T
decreases solubility.
KHenry = partial pressure of the gas in the vapor phase above the solution divided by the
concentration (in moles per liter) of the gas in solution, thus:
KH = p/[M] where p is in units of pressure (e.g., mm Hg) and [M] is in units of concentration
(e.g.., moles per liter). Changing the pressure or the concentration at constant temperature does not
change KH, hence p1/[M1] = p2/[M2].
Chem 30A
Dr Schaleger
Chapters 8 – 9
Useful Relationships
Laney College
Spring 2014
Colligative properties; depend on the concentration of particles in the solution
BP elevation of water = 0.51 ( a constant having units of deg/osmolarity) x Concentration in
#moles of particles/liter of solution (osmolarity). Thus the bp of a 0.1 M solution of KCl in water is 0.51 x
0.2 + 100 = 100.102 deg C.
FP depression of water = -1.86 deg/osmolarity) x Concentration in #moles of particless per liter
of solution (osmolarity). Thus the freezing point of a 0.1 M solution of NaCl in water is -1.86 x 0.2 =
-3.72 deg C.
Osmotic pressure: π = (n/V)RT where n/V is the osmolarity.
Definition: Osmolarity (osmol) is the sum of the molar concentrations of all dissolved particles
in a solution. Thus the osmolarity of a 0.1 M solution of BaCl2 = 0.1 + 2 x .1 = 0.3 osmol.
Molecular solutions (e.g., glucose in water), the osmolarity = molarity.