CHM 123Chapter 10

Type of nonbonding interactions

A.Ion-ion interaction (Na+ Cl-)

B.Hydrogen bonding (OH, NH, NF) (polar interaction)

C.Dipole-dipole(polar interaction)

D.Van der waals (vdw) (nonpolar molecules)

*Ion-ion interaction between ions

- electrostatic interaction between two permanent charges

Na+ Cl-

*Dipole – dipole interaction between polar molecules

*Hydrogen bonding – strongest known dipole, due to having H on N or O or F

*van der waals interaction

Greater surface area, greater van der waals

Higher MW, higher B.P (if all polarity is equal)

Straight chain vs. branches

E.g. Rank the following molecules from highest B.P to lowest B.P then provide your reasons/

water ethyl alcohol dimethyl ether propane Argon Lithium bromide

H2O CH3CH2OH CH3OCH3 CH3CH2CH3 ArLiBr

10.3-10.5 – Phase change, evaporation, vapor pressure, and boiling point

Phase Change (State Change): A change in physical form but not the chemical identity of a substance.

Consider the boling curve below to answer the following questions:

What is the melting point of this substance? ………..

What is the boling point of this substance? ………………..

How do calculate the amount of heat required during phase change?

Heat (Enthalpy) of Fusion (ΔHfusion ): The amount of energy required to overcome enough intermolecular forces to convert a solid to a liquid.

Heat (Enthalpy) of Vaporization (ΔHvap): The amount of energy required to overcome enough intermolecular forces to convert a liquid to a gas.

  • Depends on the amount of attractive (intermolecular )forces between molecules
  • Stronger the force the higher ΔHvap (or boiling point)

The heating curve of water

Example: How much energy is needed to increase the temperature of 10.4 g of cadmium from 64.0°C to 325.0°C? (the specific heat of cadmium is 0.231 J/g°C)

A particular refrigerator cools by evaporating liquefied dichlorodifluoromethane, CCl2F2. How many kilograms of this liquid must be evaporated to freeze a tray of water at 0.0oC to ice at 0.0oC? The mass of water is 525 g, the heat of fusion of ice is 6.01 kJ/mol, and the heat of vaporization of dichloromethane is 17.4 kJ/mol.

For the solid  liquid phase change in water

ΔG = ΔH – TΔS = 0 at equilibrium

Or T = ΔH/ΔS

Example: The boiling of water is 100oC, and the enthalpy change for the conversion of water to steam is ΔHvap = 40.67 kJ/mol. What is the entropy change for vaporization ΔSvap, in J/(K• mol)

Vapor Pressure of pure liquid: The partial pressure of a gas in equilibrium with liquid at a constant temperature.

At equilibrium: rate (vap) = Rate (cond.)

Intermolecular forces / Enthalpy of vaporization / Boiling point / Vapor Pressure
Low / Low / Low / High
High / High / High / Low

Clausius-Clapeyron Equation

-this gives us a way of finding the heat of vaporization, the energy that must be supplied to vaporize a mole of molecules in the liquid state.

For water, Hvap=44.0 kJ/mol and its vapor pressure is 1.0 atm at 100.0 °C. What is vapor pressure of water at 25.0 °C and at 125.0 °C?

10.11 – Phase diagram

- summarizes the effect of temperature and pressure on a substance in a closed container. Every point in this diagram represents a possible combination of temperature and pressure for the system. The diagram is divided into three areas, which represent the solid, liquid, and gaseous states of the substance

Normal: Occurs at 1 atm.

Critical Point: A combination of temperature and pressure beyond which a gas cannot be liquefied.

•Critical Temperature: The temperature beyond which a gas cannot be liquefied regardless of the pressure.

•Critical Pressure: The pressure beyond which a liquid cannot be vaporized regardless of the temperature.

Supercritical Fluid: A state of matter beyond the critical point that is neither liquid nor gas.

Triple Point: A point at which three phases coexist in equilibrium.

Refer to the phase diagram below when answering the questions on this worksheet:

1)What is the normal freezing point of this substance? ______

2)What is the normal boiling point of this substance? ______

3)What is the normal freezing point of this substance? ______

4)If I had a quantity of this substance at a pressure of 1.25 atm and a temperature of 3000 C and lowered the pressure to 0.25 atm, what phase transition(s) would occur?

5)At what temperature do the gas and liquid phases become indistinguishable from each other? ______

6)If I had a quantity of this substance at a pressure of 0.75 atm and a temperature of -1000 C, what phase change(s) would occur if I increased the temperature to 6000 C? At what temperature(s) would they occur?

Dang 1