AP Chapter 10 Notes

When a liquid is introduced into a closed container, it establishes equilibrium with its vapor:

Liquid ó vapor

The pressure of the vapor at equilibrium is referred to as the vapor pressure of the liquid

See p. 316 Know Figure 10-1

1. Independent of volume of container, provided some liquid is present. Add 0.0100 mol of liquid benzene to 1.00L flask at 25⁰C (vp benzene = 92 mm Hg). How much benzene vaporizes?

N_vapor = PV = (92/760 atm)(1.00L) ___= 0.0050mol                     RT    (0.0821 L atm/mol K)(298 K)

N_liquid = 0.0100 – 0.0050 = 0.0050 mol

If the flask were larger than about 2L, all the liquid would vaporize, equilibrium would not be established.

2. Dependent on temperature: (V.P. vs Temp) See p. 318

1. Boiling Point – temperature at which vapor bubbles form in liquid. See p. 320



Hence, boiling point varies with applied pressure, P₂. When P₂ = 760 mmHg, bp water = 100 ⁰ C. If P₂ = 1075 mmHg, bp water = 110 ⁰ C (pressure cooker). If P₂ = 5 mmHg, water boils at 0⁰ C.

2. Critical Temperature: Temperature above which liquid cannot exist. Critical pressure = vp at critical T. Since critical T of oxygen in -119 ⁰ C, liquid oxygen cannot exist at room temperature, regardless of pressure. Critical T of propane is 97⁰ C; propane is stored as liquid under pressure at room T. See Figure 10.4. Also know Critical Pressure. See p. 322. "Propane Liquid Under Pressure."

Note that:

• solid sublimes (passes directly to vapor) below triple point (0⁰ C, 5mmHG for water; 115⁰ C, 90mmHg for I₂ ).
• If line AD inclines toward P axis, melting point decreases as P increases. This behavior is observed for water, where the liquid is the more dense phase. More often, the solid is more dense, AD tilts away from the P axis, and the melting point increases with pressure. See p. 325.

DH_subl = DH_fus + DH_vap

(s à g)     (sà l)   (là g)   

For water at 0⁰Cm these quantities are 50.9, 6.0, and 44.9 kJ/mol, in that order. DH_vap >> DH_fus . The heat of sublimation, since it is the sum of the other two enthalpy changes, is the largest of the three.

Know acids HA ó H ⁺ + A ^–

There are 3 types of forces that hold molecular substances together [i.e. inter not intra] molecular.

See p. 327 in black.

1. Dispersion Forces (London Forces) Result from temporary dipoles formed in adjacent molecules. Strength depends upon how readily electrons are dispersed. Increase with molecular size, molar mass. Explains why boiling point of molecular substances ordinarily increases with molar mass. (F₂ < Cl₂ < Br₂ < I₂ ) Found in all molecular substances. See Figure 10.9. Be able to tell me a story about these. See second paragraph p. 328.
2. Dipole Forces Electrical attractive forces between + end of one polar molecule and – end of adjacent molecule.



Compare NO(bp = -151 ⁰ C) to N₂(bp =-196 ⁰ C), O₂ (bp =-183 ⁰ C)

Be able to explain this, just like example 10.4 p.329.

3. Hydrogen Bonds Unusually strong dipole force. H atom is very small and differs greatly in electronegativity from F, O, or N. Compare boiling points of Group 6 hydrides:

Lattice energy = DH for the process occurring when separated gaseous ions are packed together to form an ionic solid. See p. 338.

 

 

VI. Metals

An overview of molecular forces in relation to protein structure

A great site on Forces

An OK site on forces (if you still don't understand)

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