KMT, Liquids PDF

As identified in General Chemistry 1, matter exists in three different phases solid, liquid and gas. Some matter can also exist in all three states. One example is water. At room temperature, water is a liquid, and the molecules in it move slowly. When water is heated, its liquid state w...

As identified in General Chemistry 1, matter exists in three different phases solid, liquid and gas. Some matter can also exist in all three states. One example is water. At room temperature, water is a liquid, and the molecules in it move slowly. When water is heated, its liquid state will change to gas; the molecules will be moving very fast and taking up space everywhere. When heat is reduced, the vapor molecules slow down and gradually turn back into liquid. When frozen, the molecules will be extremely slow and move very little. They will hold on to each other turning the water into a solid. Lastly, placing the ice at room temperature will make the ice a liquid.  You have previously learned that matter has different characteristics. Ice melts easier than salt; ethanol evaporates faster than water; hexane has a higher boiling point than methane; and salt is soluble in water but not in nonpolar liquids. In Chemistry 2, you will go beyond these and discuss the various intermolecular forces of attraction in association to these properties of liquids and solids.  SOLID 1. Closely packed and orderly arranged. 2. Particles vibrate and rotate about a fixed position. 3. Moves very slow. 4. Attractive force between particles are very strong.  LIQUID 1. Less closely packed than in a solid and disorderly arranged. 2. Particles slide over each other. 3. Motion of particle is low. 4. Has a strong attractive forces between particles.  GAS 1. Particles are very far apart and disorderly arranged. 2. Particles move about at great speed. 3. Motion of particle is high. 4. Has a very weak attractive forces.  INTRAMOLECULAR FORCES Exists inside the molecule. Maybe ionic ( attraction between cations and anions), covalent ( sharing of electrons), and metallic ( attraction between metal cations and delocalized valence electrons).  INTERMOLECULAR FORCES Occur between neighboring molecules as a result of partial charges or between ions and molecules. Usually called Van der Waals forces The types are ion-dipole, Dipole- dipole, London dispersion, H- bond, Dipole induced dipole  ION – DIPOLE FORCES Results when an ion and the partial charge found at the end of a polar molecule attract each other. Important in solutions of ionic substances. Dissolving any ionic compound in water Example: Calcium chloride, Sodium oxide, Aluminum bromide. DIPOLE – DIPOLE FORCES Weaker than an ion-dipole. Polar molecules attract each other when unlike charges are close together and repel each other when like charges are close together. Example are HCl, PCl3, H2Se. Between two polar molecules The more polar the substance, the stronger its dipole-dipole interaction. The higher the dipole moment, the higher the boiling point.  LONDON DISPERSION FORCES More common in nonpolar molecules like Cl2, He, CH4, and CO2. As London dispersion forces increase, the boiling and melting points of covalent substances increase with increasing molecular mass. The longer the chain, the higher the boiling point like in C2H6 and C5H12  H - BONDS Interaction between a hydrogen atom bonded to an electronegative F, O, or N atom. Stronger than dipole-dipole forces and dispersion forces. H – bond in hydrogen compounds has an increase boiling point due to increased dispersion forces.  Dipole – Induced Dipole For polar and nonpolar molecules In the presence of a polar molecule, a nonpolar molecule is forced to become a dipole. The attractive force that predominates between an ion and a nonpolar molecule. Example is between HCl and O2 molecule, CO2 in H2O  ACTIVITY #1 (CHEM 2) Determine the type of intermolecular forces that exist in each of the following systems. 1. MgCl2 and H2O 6. HF 2. C6H14 7. SO2 3. C6H14 and H2O 8. Na2SO4 and H2O 4. CH3CH2OH 9. CH3COOH and H2O 5. H2S and HBr 10. N2 PROPERTIES OF LIQUIDS Due to intermolecular forces liquids exhibit the following properties: 1. Viscosity 2. Surface Tension 3. Capillarity 4. Evaporation 5. Vapor pressure 6. Boiling point  VISCOSITY The ability of a fluid to resist flowing. Nonpolar molecules like benzene (C6H6), pentane (C5H12) and carbon tetrachloride (CCl4)have low viscosities due to weak intermolecular forces (London dispersion). Polar molecules like glycerol (C3H5(OH)3) and syrup have high viscosities because of H-bonding  The viscosity of a liquid decreases with increasing temperature because the average kinetic energy of molecules is greater. Viscosity can be measured using a viscometer.  SURFACE TENSION The energy required to increase the surface area of a liquid. An example are small insects walk on bodies of water, needles float on water and water beaded up on a newly waxed car. These happen due to unequal intermolecular forces at the surface of the liquid. To increase the surface area of a liquid, molecules move to the surface by breaking some attractions in the interior which requires energy (surface tension).  Surfactants (surface-active ingredients) such as detergents, soaps and biological fat emulsifiers decrease the surface tension of water and destroy H-bonds.  CAPILLARITY The rising of the blood or any liquid in a tube is called capillarity or capillary action. It is observed when you go for simple blood tests and in the transport of water from the roots of a plant. This results from a competition between the intermolecular forces within the liquid molecules (cohesive forces) and those between the liquid molecules and the walls of the tube (adhesive forces). COHESIVE force – the attractive force between molecules of the same substance. ADHESIVE force – the attractive force between molecules of different substances.  Evaporation, Vapor Pressure and Boiling Point Evaporation is the escape of a liquid particles into the gaseous or vapor state. The escape of a more energetic molecules on a liquid surface reduces the average kinetic energy of the remaining molecules, this causes the cooling effect when perspiration evaporates from the skin’s surface like in alcohol or acetone.  When molecules of liquid in a closed container reach equilibrium with its vapor after some time, there is no more change in the liquid level (saturated vapor pressure). However, as the vapor particles increase, some collide with the liquid surface and return to the liquid state (condensation).  Volatility is the ability of a substance to vaporize. It is proportional to its vapor pressure. The higher the vapor pressure, the more volatile the liquid. An increase in temperature decreases the intermolecular force of attraction in a liquid, thereby also increasing vapor pressure.  Boiling point is the temperature wherein the saturated vapor pressure is equal to the external pressure. This property changes as pressure changes. The effect of high altitudes and lower boiling point temperature can be counteracted by using a pressure cooker.  Properties of Water 1. Water has high surface tension. 2. Water has high boiling point. 3. The density of solid water or ice is less than the density of liquid water due to the stronger H-bond in ice. 4. Water has a high heat of vaporization ( the amount of heat required to change a given amount of liquid into gas). 5. Water is a good solvent due to its polar nature.