13.1 States of Matter: A Review 13.2 Properties of Liquids A. Evaporation B. Vapor Pressure C. Surface Tension 13.3 Boiling Point and Melting Point

Transcription

1

2 13.1 States of Matter: A Review 13.2 Properties of Liquids A. Evaporation B. Vapor Pressure C. Surface Tension 13.3 Boiling Point and Melting Point 13.4 Changes of State 13.5 Intermolecular Forces 13.6 Hydrates 13.7 Water, a Unique Liquid

3 States of Matter: A Review Gases: contain particles that are far apart, in random motion, and independent of one another. Little contact No attractive forces Random motion Solids: contain particles very close in space and maintain a rigid shape. Significant attractive forces exist between particles. Close contact Strong attractive forces Rigid shape

4 States of Matter: A Review Liquids: intermediate between gases and solids. Contain particles close to one another but have fluidity (can assume the shape of a container). Significant attractive forces exist between particles in a liquid. Close contact Some attractive forces Fluid shape

5 Evaporation Evaporation or Vaporization: Escape of molecules from the liquid to the gas phase. Liquid Vapor Molecules in the liquid state have different kinetic energies (KEs). Those with higher KEs can overcome attractive forces between particles and escape to the gas phase.

6 Sublimation Phase change from the solid to gas phase that bypasses the liquid state. Solid Vapor Examples CO2 (s) CO2 (g) I2 (s) I2 (g)

7 Vapor Pressure Molecules from the liquid phase can escape to the vapor phase through evaporation. Molecules in the gas phase can strike the surface of the liquid and return to the liquid phase. This process is called condensation. In a closed container, an equilibrium develops between molecules evaporating and condensing. liquid evaporation condensation vapor

8 Vapor Pressure Vapor pressure: pressure exerted by a vapor in equilibrium with its liquid phase.

9 Vapor Pressure Vapor pressure: pressure exerted by a vapor in equilibrium with its liquid phase. Independent of the quantity of liquid or its surface area. Increases with increasing temperature. Depends on the strength of attraction between molecules in the liquid state. Volatile liquids: very weak attractive forces between molecules. Evaporate very rapidly at ambient temperature. Have high vapor pressures as a result.

10 Vapor Pressure Measure using a barometer. Measuring Vapor Pressure of a Liquid Vapor from the liquid exerts a force on the Hg and pushes the column downward. The difference in height relative to vacuum provides the vapor pressure for the liquid.

11 SURFACE TENSION Resistance of a liquid to an increase in surface area. Molecules on a liquid surface are strongly attracted by molecules within the liquid. Surface tension increases with increasing attractive interactions between molecules. Mercury droplets form spheres due to surface tension.

12 CAPILLARY ACTION Spontaneous rise of a liquid in a narrow tube. Cohesive forces exist between water molecules in a liquid. Adhesive forces exist between water molecules and the walls of the container. When the cohesive forces between molecules are less than the adhesive forces between liquid and container, the liquid will move up the walls of the container.

13 Capillary Action Shape of the meniscus reflects the relative strength of cohesive forces within the liquid and adhesive forces between the liquid and the tube. If convex: adhesive forces < cohesive forces If concave: adhesive forces > cohesive forces Hg H2O

14 BOILING POINT Temperature at which the vapor pressure of a liquid is equal to the external pressure above the liquid. Where is the boiling point of a liquid higher, at or above sea level? At sea level. The atmospheric pressure is higher.

15 Boiling Point Normal boiling point: temperature when the vapor pressure is 1 atm Vapor Pressure Curve Normal boiling points: Water: 100 ºC Ether: 35 ºC Ethyl Alcohol: 78 ºC

16 FREEZING POINT Freezing/melting point: the temperature at which the solid phase of a substance is in equilibrium with its liquid phase. solid melting freezing liquid While both phases are present, the temperature remains constant. The energy is used to change the solid to the liquid phase.

17 CHANGES OF STATE Heat of fusion: energy required to change 1 g of a solid at its melting point to a liquid. Heat of vaporization Boiling Melting Heat of fusion Heat of vaporization: energy required to change 1 g of a liquid to vapor at its normal boiling point.

18 INTERMOLECULAR FORCES Attractive forces between molecules. These forces allow for formation of liquids and solids. The degree of intermolecular forces correlates with a compound s physical properties. Example: The stronger the interaction between molecules in a liquid, the higher the boiling point and the lower the vapor pressure.

19 TYPES OF INTERMOLECULAR FORCES Dipole-Dipole Attractions In covalent molecules, due to different atoms having different electronegativities, molecules are polar. When polar molecules are put together, they will align to permit interaction between oppositely polarized portions of the molecules. The interaction of two polar H2O molecules. These interactions between dipoles in different molecules are called dipole-dipole forces.

20 The Hydrogen Bond Water has very high melting and boiling points, and heats of fusion and vaporization. These anomalous properties are due to strong attraction between water molecules due to hydrogen bonding, a special type of dipole-dipole attraction.

21 The Hydrogen Bond Hydrogen bonds: one type of strong intermolecular force/attraction between molecules. Hydrogen bonds are much weaker than ionic or covalent bonds which are intramolecular forces. Hydrogen Bonding between H2O molecules.

22 The Hydrogen Bond To form hydrogen bonds, a compound must have covalent bonds between hydrogen and F, O or N (a very electronegative element). Can hydrogen bond. Cannot hydrogen bond. (No H attached to oxygen).

23 Which of the following molecules would be expected to participate in hydrogen bonding?

24 London Dispersion Forces Molecules without dipoles can also interact with one another. These interactions between nonpolar molecules and noble gases are called London dispersion forces. London forces arise from uneven, instantaneous charge distributions due to electron movement in nonpolar molecules.

25 London Dispersion Forces This instantaneous dipole can then induce a dipole in a neighboring nonpolar molecule, resulting in a small attraction between particles. London forces are very weak forces. Generally become more important as the size of the molecule increases. Larger sizes provide more possible electrons to provide dipoles.

26 London Dispersion Forces Which of the following molecules would have the largest London dispersion forces? a. CH4 b. C4H10 c. C15H32 d. C8H18 The largest hydrocarbon (i.e., having the largest molar mass) will have the strongest London forces.

27 Hydrates Hydrates are solids that contain water molecules as part of their crystalline structure. The formula lists the anhydrous (without water) formula of the compound. The number of waters present per structural unit (water of hydration) are then given. CaCl2 2H2O Hydrates are named by placing a prefix corresponding to the number of water molecules, followed by hydrate CaCl2 2H2O calcium chloride dihydrate FeCl3 6H2O iron(iii) chloride hexahydrate

28 Hydrates Hydrates will often decompose by losing water upon heating. CuSO4 5 H2O (s) 250 C CuSO4 (s) + 5 H2O (g)

29 Calculate the percent water in Epsom salts MgSO4 7H2O (s). 1. Calculate the molar mass of the compound. Molar Mass MgSO4 7H2O (s) = (18.02) = g 2. Calculate the % water of the compound. % water = Mass water Molar mass g x 100 = x 100 = % g

30 Hydrates Practice What is the percent water in CuSO4 5H2O (s)? a % b % c % d % 1. Calculate the molar mass of the compound. Molar Mass CuSO4 5H2O (s) = (18.02) = g 2. Calculate the % water of the compound. % water = Mass water Molar mass g x 100 = x 100 = % g

31 Water: A Unique Liquid Water covers 75% of the Earth s surface; 97% of all water resides in the oceans. Water constitutes 70% of a human body by mass. Physical Properties of Water Colorless, odorless, tasteless liquid. More dense in liquid than solid phase (why ice floats). High boiling point, high heat of fusion/vaporization due to hydrogen bonding.

32 Water: A Unique Liquid Structure of Water Molecules Two OH bonds are formed by the overlap of 1s orbitals on H with orbitals on the O. The molecular geometry of water is bent, due to the two lone pairs on oxygen. Water has a permanent dipole due to the molecules shape and the polar O-H bonds.

33 Water: A Unique Liquid Sources of Water for Human Consumption Climate change and increased demand for fresh water make finding and sustaining sources of potable water critical for future generations. Strategies to Sustain Water Supplies 1. Reclamation of wastewater Currently used in agriculture and industry 2. Desalination of seawater Expensive, but useful for countries near the ocean. 3. Low temperature distillation At low pressure, water s boiling point is reduced. Less energy is required to separate the salts by boiling. 4. Combustion of H2 H2 and O2 react very exothermically to produce water.

34 Osmosis: process by which water flows through a membrane from a region of more pure water to a region of less pure water. Water flows into the raisin to dilute the sugar. The size of the raisin expands.