CHEM Ch.8 : Gases, Liquids, & Solids
MP, BP, Heat of Fusion and Heat of Vaporization
If intermolecular forces are strong then large amount of heat must be added to overcome these forces, and the heats of fusion and vaporization will be large.
Vapor Pressure
The partial pressure of vapor molecules in equilibrium with a liquid.
Unit of Pressure
mmHg aka torr
Melting Point (MP)
The EXACT temperature at which solid and liquid are in equilibrium.
Kinetic Molecular Theory w/Gas
Each particle in a gas acts independently of all others because there are no attractive forces between them and they are so far apart.
Standard Molar Volume of any ideal gas at STP
22.4 L/mole
Atmospheric Pressure
A column of air weighing 14.7 lb presses down on each square inch of the earth's surface at sea level. A blanket of air pressing down on us. Atmospheric pressure is not constant, it varies slightly from day to day depending on the weather. Density of air is at greatest near the earth's surface, and decreases with increasing altitude. For example, it's 14.7 psi at seal level but only 4.7 psi on summit of Mt.Everest.
States of Matter & Their Changes
A compound exists under a given set of conditions depends on the relative strength of the attractive forces between particles compared to the kinetic energy of particles. Ex. Gases - attractive forces between particles are weak, kinetic energy is strong because particles can move freely Ex. Liquids - attractive forces between particles are strong and so is kinetic energy Ex. Solids - attractive forces between forces are stronger, kinetic energy is lower because particles are held in a specific arrangement.
Intermolecular Force
A force that acts between the molecules and holds molecules close to one another. Act between different molecules rather than within an individual molecule. Three Types: 1. Dipole - Dipole 2. London Dispersion 3. Hydrogen Bonding
Ideal Gas
A gas that obeys all the obeys all the assumptions of the kinetic-molecular theory.
Kinetic - Molecular Theory of Gases
A group of assumptions that explain the behavior of gases.
Surface Tension
A property of liquid. Resistance of a liquid to spreading out and increasing its surface area caused by difference between intermolecular forces experienced by molecules at the surface of the liquid and those experienced by molecules in the interior. Ex: beading up of water on a newly waxed car or the ability of a water strider to walk on water.
Gas Laws
A series of laws that predict the influence of pressure, volume, and temperature on any gas or mixture of gases.
Crystalline Solid
A solid whose atoms, molecules, or ions are rigidly held in an ordered arrangement.
Amorphous Solid
A solid whose particles do not have an orderly arrangement.
Normal Boiling Point
At a liquids boiling point, its vapor is equal to atmospheric pressure.
Standard Temperature and Pressure (STP)
Celsius = 0/Kelvin = 273.15 1 atm = 760 mmHg
Favored Process
Delta H = Negative When energy is released Delta S = Positive When disorder is decreased Delta G = Negative The equation of free-energy equation is used if the two factors (Delta H & Delta S) are not in agreement. This helps to determine if the process is favored at a given temperature. If Delta G is negative, then it is favored, if
Unfavored Process
Delta H = Positive Delta S = Negative Delta G = Positive
Barometer
Instrument used to measure pressure. Atmospheric pressure is 760 mm
Changes of State
Low Temperature: Delta H is larger than T Delta S, Delta G = positive. Melting does NOT occur. High Temperature: Delta H is lesser than T Delta S, Delta G = negative. Melting does occur.
Enthalpy Change (Delta H)
Measure of heat absorbed or released during a given change of state. Ex. Melting of a solid to a liquid, heat is absorbed. Delta H = Positive (endothermic) Ex. Reverse process, freezing of liquid to a solid, heat is released. Delta H = Negative (exothermic)
Entropy Change (Delta S)
Measure of the change in molecular disorder or freedom that occurs during a process. Ex. Melting of a solid to a liquid, disorder increases because freedom of motion Delta S - Positive Ex. Reverse process, freezing liquid to solid, disorder decreases. Delta S - Negative
Charle's Law (Volume & Temperature)
Notice atm stays the same, but temperature affects the volume.
London Dispersion Forces
Short-lived attractive force due to the constant motion of electrons within molecules. All molecules experience this force, regardless of structure. Weak forces, but increase with molecular weight and amount of surface area available for interaction between molecules.
Hydrogen Bonds
The attraction between a hydrogen atom bonded to an electronegative O, N, or F atom and another nearby electronegative O, N, or F atom. Strong attraction. Primary intermolecular force that holds hug biomolecules in shapes needed to play their essential roles in biochemistry. (Ex. DNA are held together by hydrogen bonds) A special kind of dipole-dipole bond Silly Reminder: ONF (on/off)
Dipole - Dipole Force
The attractive force between positive and negative ends of polar molecules. Weak Forces. It is used to determine the difference in boiling points between polar and nonpolar molecules.
Change of State
The change of a substance from one state of matter (gas, liquid, or solid) to another. Characterized by a free-energy change. AKA phase change
Gas Constant (R)
The constant R in ideal gas law, PV=nRT
Partial Pressure
The contribution of a given gas in a mixture to the total pressure.
Pressure (P)
The force (F) per unit area (A) pushing against a surface. P=F/A
Vapor
The gas molecules are in equilibrium with a liquid
Viscosity
The measure of a liquid's resistance to flow.
Gay Lussac's Law
The pressure of gas is directly proportional to the temperature in kelvins for a fixed amount of gas at a constant volume. As temperature goes up, the pressure goes up.
Heat of Vaporization
The quantity of heat needed to completely vaporize one gram of liquid once it has reached its boiling point.
Heat of Fusion
The quantity of heat required to completely melt one gram of a substance once it has reached its melting point.
Boiling Point (BP)
The temperature at which liquid and gas are in equilibrium.
Dalton's Law
The total pressure exerted by a gas mixture is the sum of the partial pressure of the components in the mixture.
Boyle's Law (Volume & Pressure)
The volume of gas decreases proportionately as it's pressure increases. For example if the pressure of a gas sample is doubled, the volume is halved. The kinetic energy is constant, the number of collisions increase as the interior surface of the area of the container decreases, leading to an increase pressure.
Avogadro's Law
Volume is directly proportional to the molar amount, n, at a constant temperature and pressure. As the number of moles goes up, the volume also goes up.
Idea of State Change
When solid is heated, more and more energy is added, the molecules begin to stretch, bend, and vibrate more vigorously, and atoms or ions wiggle about with more energy. Finally, if enough energy is added, the motions become vigorous enough, particles start to break free from one another and the substance starts to melt.
Heat of Vaporization
Where molecules carries away a large amount of heat when it evaporates.