States Of Matter (69-91) 15%

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Intermolecular Forces

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-substances that are primarily made up of covalent bonds, which are weaker, can be solid or liquid, and their state will depend on the presence and type of intermolecular forces.
-Two main types of intermolecular forces that exist b/w molecules are dipole-dipole forces (including hydrogen bonds) and London Dispersion Forces.

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Dipole-Dipole Forces

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-take place when two or more neutral, polar molecules are oriented such that their positive (+) and negative (-) ends are close to each other.
-tends to be in the solid or liquid state. For molecules that are about the same size and weight, the strength of the dipole-dipole forces increases as the degree of polarity increases.
-The more stronger the dipole-dipole forces it will form with itself and other molecules.
-One very important and unique case of the dipole-dipole attraction is known as HYDROGEN BONDING. Hydrogen bonds are not true bonds: they're just strong attractive forces b/w the hydrogen on one molecule and a highly electronegative atom on a nearby molecule. Hydrogen bonds most commonly fomr b/w hydrogen atoms and fluorin, oxygen, or nitrogen.

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London Dispersion Forces- Weak Inter-molecules Forces

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-relatively weak forces of attraction that exist b/w nonpolar molecules and noble gas atoms.
-Ex: argon (a noble gas) and octane (a hydrocarbon; C8H18).
-these types of attractive forces are caused by a phenomenon known as INSTANTANEOUS DIPOLE FORMATIONS. In this process, electron distribution in the individual molecules suddenly becomes asymmetrical, and the newly formed dipoles are now attracted to one another.
-The ease with which the electron cloud of an atom can be distorted to become asymmetrical is called the molecule's POLARIZABILITY.
-Larger nonpolar molecules tend to have stronger London dispersion forces.
-For nonpolar molecules, the farther you go down the group, the stronger the London dispersion forces.

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Solids

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-molecules generally held together by ionic or strong covalent bonding with attractive forces b/w atoms that are very strong.
-There are 2 main categories of solids-crystalline solids and amorphous solids.
-CRYSTALLINE SOLIDS: are those in which the atoms, ions, or molecues that make up the solid exist in a regular, well-defined arrangement.
-AMORPHOUS SOLIDS: do not have much order in their structures. Though their molecules are close together and have little freedom to move, they are not arranged in a regular order as are those in crystalline solids.

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Types of Crystalline Solids

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-IONIC SOLIDS: made up of positive and negative ions and held together by electrostatic attractions. They're characterized by very high melting points and brittleness and are poor conductors in the solid state. Ex: NaCl
-MOLECULAR SOLIDS: made up of atoms or molecules held together by London dispersion forces, dipole-dipole forces, or hydrogen bonds. Characterized by low melting points and flexibility and are poor conductors. Ex: Sucrose
-COVALENT-NETWORK (ALSO CALLED ATOMIC) SOLIDS: made up of atoms connected by covalent bonds; the intermolecular forces are covalent bonds as well. Characterized as being very hard with very high melting points and being poor conductors. Ex: diamond, graphite, and the fullerenes.
-METALLIC SOLIDS: Made up of metal atoms that are held together by metallic bonds. Characterized by high melting points, can range from soft and malleable to very hard , and are good conductors of electricity.

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Liquids

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-made up of molecules that contain covalent bonds and have strong intermolecular attractive forces.
-have no definite shape but do have a definite volume, and they are not easily compressible.

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Gases

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-consists of atoms and molecules that are covalently bonded, and their intermolecular forces are very weak.
-A gas has no definite shape.

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Heat Of Fusion (H(fus))

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-the amount of energy that must be put into the substance for it to melt.
-Ex: the heat of fusion of water is 6.01 kJ/mol, or in other terms, 80 cal/g.

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Heat Of Vaporization (H(vap))

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-the amount of energy needed to cause the transition from liquid to gas.

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Energy (in Calories)

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-Energy (in Calories) = mC(p)#T
where
-m=the mass of the substance (in grams)
-C(p)=the specific heat of the substance (in cal/g C)
-#T=the change in temperature of the substance (in either Kelvins or C, but make sure all your units are compatible!)

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Specific Heat

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-the heat required to raise the temperature of 1 g of a substance by 1C.

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Gas Ideal State

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1. All gas particles are in constant, random motion.
2. All collisions b/w gas particles are perfectly elastic (meaning that the kinetic energy of the system is conserved).
3. The volume of the gas molecules in a gas is negligible.
4. Gases have no intermolecular attractive or repulsive forces.
5. The average kinetic energy of the gas is directly proportional to its Kelvin temperature and is the same for all gases at a specified temperature.

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Properties of Gas

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-Only four measurable properties are used to describe a gas: its quantity, temperature, volume, and pressure. THe quantity (amount) of the gas is usually expressed in moles (n). The temperature, T, of gases must always be converted to the Kelvin temperature scale (the absolute temperature scale). The volume, V, of a gas is usually given in liters. Finally the pressure, P, of a gas is usually expressed in atmospheres.
-Gases are often discussed in terms of STANDARD TEMPERATURE AND PRESSURE (STP), which means 273K (or 0C) and 1 atm.

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Gas Pressure

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-Gas pressure is a gauge of the number and force of collisions b/w gas particles and the walls of the container that holds them.
-The SI unit for pressure is teh pascal (Pa), but other pressure terms include ATMOSPHERE (ATMS), MILLIMETERS OF MERCURY (MMhG), AND TORR.

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Units for Conversion of Gas Pressure (MEMORIZE)

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760 mmHg
760 torr
1.00 atm
101,325 Pa
101.325 kPa

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Boyle's Law (1/6)
P1V1 = P2V2
-ONLY USE KELVIN

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-simply states that the volume of a confined gas at a fixed temperature is inversely proportional to the pressure exerted on the gas.
-Ex: When the pressure around a balloon increases, the volume of the balloon decreases, and likewise, when you decrease the pressure around a balloon, its volume will increase.

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Charles's Law (2/6)
V1/T1 = V2/T2
-ONLY USE KELVIN

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-states that if a given quantity of gas is held at a constant pressure, its volume is directly proportional to the absolute temperature.
-Ex: as the temperature of the gas increases, the gas molecules will begin to move around more quickly land hit the walls of their container with more force-thus the volume will increase.

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Avogadro's Law (3/6)
V = constant x n(where n is the number of moles of the gas)
-ONLY USE KELVIN

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-the volume of a gas at a given temperature and pressure is directly proportional to the quantity of the gas.
-EQUAL VOLUMES OF GASES UNDER THE SAME CONDITIONS OF TEMPERATURE AND PRESSURE CONTAIN EQUAL NUMBER OF MOLECULES.
-says that the volume of a gas maintained at constant temperature and pressure is directly proportional to the number of moles of the gas.

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The Ideal Gas Law (4/6)
PV = nRT
-ONLY USE KELVIN

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-the most important gas law for you to know: it combines all of the laws you learned about in this chapter thus far, under a set of standard conditions.

PV = nRT
-where P=Pressure (atm), V=Volume (L), n=number of moles (mol), R= 0.08206 L*atm/mol*K, and T=Temperature (K)

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Dalton's Law of Partial Pressures (5/6)
P (total) = P1 + P2 + ...P(n)

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-Dalton's law states that the pressure of a mixture of gases is the sum of the pressures that each of the individual gases would exert if it were alone.

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Graham's Law of Diffusion and Effusion (6/6)

Rate of Effusion of Gas 1/Rate of Effusion of Gas 2
=
Sqr Root (FW2/FW1)

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-states that the rates of effusion of two gases are inversely proportional to the square roots of their molar masses at the same temperature and pressure.
-Effusion is the term used to describe the passage of a gas through a tiny orifice into an evacuated chamber. The RATE OF EFFUSION measure the SPEED at which the gas travels through the tiny hole into a vacuum.
-Diffusion is the term used to describe the spread of a gas throughout a space or throughout a second substance.

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Densities Of Gases

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-the densities of gases are reported in g/L, not g/mL as found for solids and liquids.
-Density is equal to mass per unit of volume. To calculate the density of a gas at standard temperature and pressure, you take the molecular formula weight of the gas (grams per mole-from the periodic table) and divide that by the STANDARD MOLAR VOLUME FOR A GAS, which is 22.4 L per mole.

-Density = FW / 22.4
where the formula weight (FW) is in g/mol, and the standard molar volume is 22.4 L/mol.

-Example: What is the density of helium gas at STP?

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PROPERTIES OF SOLUTIONS

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-A SOLUTION is a homogenous mixture of two or more substances that exist in a single phse. There are two main parts to any solution. The SOLUTE is the component of a solution that is dissolved in the solvent; it is usually present in a smaller amount than the solvent. The SOLVENT is the component into which the solute is dissolved, and it is usually present in greater concentration.

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General Rule of Thumb: Like dissolves like

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-The general rule of thumb for solutions is the idea that 'LIKE DISSOLVES LIKE.'
-Polar, ionic substances are soluble in polar solvents, while nonpolar solutes are soluble in nonpolar solvents.
-For example, alcohol and water, which are both polar, can form a solution and iodine and carbon tetrachloride, which are both nonpolar, make a solution. However iodine will not readily dissolve in polar water.

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Colloid

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-One type of mixture that is not a solution is known as the colloid. In a COLLOID, particles are b/w 100 and 1,000 nm in size- still too small for our eyes to distinguish, but particles this small will not settle.
-Ex: gelatin, fog, smoke, and shaving cream.

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Suspensions

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-have much larger particles: usually over 1,000 nm. Particles in a suspension will settle on standing, can often be seperated by a filter, and may scatter light, but they are usually not transparent.
-Ex: muddy water, paint, and some medicines, like Pepto-Bismol.

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The Solution Process

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-In order for a solute to be dissolved in a solvent, the attractive forces b/w the solute and solvent particles must be great enough to overcome the attractive forces w/in the pure solvent and pure solute. The solute and the solvent molecules in a solution are expanded compared to their position w/in the pure substances.
-The process of expansion, for both the solute and solvent, involves a change in the energy of the system: this process can be either exothermic or endothermic. After dissolving, the solute is said to be fully SOLVATED (usually by dipole-dipole or ion-dipole forces), and when the solvent is water, the solute is said to be HYDRATED.
-The term SOLUBILITY refers to the maximum amount of material that will dissolve in a given amount of solvent at a given temperature to produce a stable solution.

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Degrees of Saturation

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-If a solution is UNSATURATED, the solvent is capable of dissolving more solute. When the solution is SATURATED, the solvent has dissolved the maximum amount of solute that it can at the given temperature. At this point we say that the solution is in a state of DYNAMIC EQUILIBRIUM- the processes of dissolving and precipitation are happening at the same rate. A SUPERSATURATED solution is one in which the solvent contains more solute than it can theoretically hold at a given temperature.

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Molarity (M)
M = moles of solute/liters of solution

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-The molarity of a solution is a measure of the number of moles of solute per liter of solution.

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Dilution

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-is the process of taking a more concentrated solution and adding water to make it less concentrated.
-The more concentrated solution before the dilution is performed is known as the STOCK solution.

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Mass Percent (Weight Percent)
Mass Percent = Grams of solute/g of solute + g of solvent (all x 100)

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-is another way of expressing its concentration.
-is found by dividing the mass of the solute by the mass of the solution and multiplying by 100; so a solution of NaOH that is 28% NaOH by mass contains 28g of NaOH for each 100g of solution.

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MolaLity (m)
m = moles of solute / Kilograms of solvent

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-is a measure of the number of moles of solute per kilogram of solvent.
-Whereas the molarity of a solution is dependent on the volume of the solution, the MOLALITY is dependent on the mass of the solvent in the solution.

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Electrolytes

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-Certain solutions are capable of conducting an electric current and these solutions are referred to as Electrolytes.
-STRONG ELECTROLYTES consist of solutes that dissociate completely in solution. Strong acids, strong bases, and soluble salts are in this category.
-NONELECTROLYTES are substances that are predominantly covalently bonded, generally will not produce ions in solution, and therefore are considered nonconductors.
-WEAK ELECTROLYTES consist of solutes that dissociate only a little in solution. Weak acids, weak bases, and slightly soluble salts are in this category.

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Colligative Properties

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-Properties of solutions that depend on the number of solute particles present per solvent molecule are called COLLIGATIVE PROPERTIES. The concentration of solute in a solution can affect various physical properties of the solvent including its freezing point, boiling point, and vapor pressure.

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Freezing Point Depression

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-the freezing point of a substance is defined as the temperature at which the vapor pressure of the solid and the liquid states of that substance are equal. If the vapor pressure of the liquid is lowered, the freezing point decreases.

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Calculation for the Effect of Solute Particles

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ΔT(f) = K(f) x m(solute) x i
-ΔT(f)=the change in freezing point
-K(f)=molal freezing point depression constant for the substance (for water= 1.86C/m)
-m=molality of the solution
-i=number of ions in solution (this is equal to 1 for covalent compounds and is equal to the number of ions in solution for ionic compounds)

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Boiling Point Elevation

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-the boiling point of a substance is the temperature at which the vapor pressure equals atmospheric pressure.

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Calculating the change in Boiling Point

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ΔT(b)=K(b) x m(solute) x i
-K(b)=molal boiling point elevation constant (for water = 0.51C/m)