IMF, properties of liquids, and clausius-clapeyron.pptx

discussion and activity on properties of liquids

1. Intermolecular Forces and Trends Forces that exist between molecules Ion-Dipole – ion and polar molecule interact Hydrogen Bonding – (H—F); (H – O); (H – N) Dipole-Dipole – for polar molecules London Dispersion -- can form between any molecules ↑ Intermolecular Force ↑ Boiling Point ↑ Intermolecular Force ↑Surface Tension ↑ Intermolecular Force ↑Viscosity ↓ Intermolecular Force ↑Vapor Pressure

2. Intermolecular Forces and Trends Example: CH4 H2S CCl4 NH3

3. Properties of Liquids Surface Tension is the magnitude of the force that controls the shape of the liquid. Cohesion is the tendency of a compound to interact with itself. Adhesion is the tendency of a compound to interact with another compound Capillary rise or capillarity is a phenomenon in which liquid spontaneously rises or falls in a narrow space such as a thin tube or in the voids of a porous material. If θ < 90°, cos θ is positive, so h is positive, i.e. liquid rises in a capillary tube. If θ > 90°, cos θ is negative, so h is negative, i.e. liquid falls in a capillary tube.

4. Properties of Liquid Viscosity of a liquid is a measure of its resistance to flow Factors Affecting Viscosity: Effect of Temperature: when the temperature of the liquid increases, its viscosity decreases Molecular weight: when the molecular weight of the liquid increases, its viscosity increases. Pressure: increase pressure on liquids, the viscosity increase.   volume of fluid (V) that flows down a small-diameter capillary tube per unit of time (t) is proportional to the radius of the rube (r), the pressure pushing the fluid down the tube (P), the length of the tube (l), and the viscosity of the fluid ( η )

5. Clausius-Clapeyron Equation allows us to estimate the vapor pressure at another temperature, if the vapor pressure is known at some temperature, and if the enthalpy of vaporization is known. ΔHvap is the Enthalpy (heat) of Vaporization; R is the gas constant (8.3145 J/mol-K); P1 and P2 are the vapor pressures at two temperatures T1 and T2 The Clausius-Clapeyron equation can be also applied to sublimation

6. Sample Problem #1: The vapor pressure of water is 1.0 atm at 373 K, and the enthalpy of vaporization is 40.7 kJ mol -1 . Estimate the vapor pressure at temperature 363 and 383 K respectively. Clausius-Clapeyron Equation Answer: 1.409 atm

7. Sample Problem #2: The vapor pressures of ice at 268 K and 273 K are 2.965 and 4.560 torr respectively. Estimate the heat of sublimation of ice. Clausius-Clapeyron Equation Answer: 52,370 J/mol

8. Sample Problem #3: Calculate ΔHvap for ethanol, given vapor pressure at 40 ° C = 150 torr. The normal boiling point for ethanol is 78 °C. Clausius-Clapeyron Equation Answer: 39.0 kJ/mole

9. Naphthalene, C10H8, melts at 80.2°C. If the vapour pressure of the liquid is 1.3 kPa at 85.8°C and 5.3 kPa at 119.3°C, use the Clausius–Clapeyron equation to calculate (a) the enthalpy of vaporization, (b) the normal boiling point, and (c) the enthalpy of vaporization at the boiling point.