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CHEM 115: Exam 2
Pressure
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The force exerted per unit area of surface
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Acceleration
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The change of speed per unit time. m/s
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Force
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Mass x constant acceleration of gravity
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Pressure
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Force/area
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Barometer
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Device for measuring the pressure of the atmosphere
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Manometer
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Device that measures the pressure of a gas or liquid in a vessel
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Millimeters of mercury
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Aka torr. A unit of pressure equal to that exerted by a column of mercury m high at 0.00 degrees Celsius
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Atmosphere
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Unit of pressure equal to exactly 760 mmHg
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P=gdh
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Relationship between pressure and the height of a liquid column in a barometer or manometer
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Boyle's Law
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The volume of a sample of gas at a given temperature varies inversely with the applied pressure
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Equation for Boyle's law
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PV=constant
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John Dalton & Joseph Louis Gay-Lussac theory
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A sample of gas at a fixed pressure increases in volume linearly with temperature
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Charles Law
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The volume occupied by any sample of gas at a constant pressure is directly proportional to the absolute temperature
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Equation for Charles Law
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V/T
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Combined Gas law
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The volume occupied by a given amount of gas is proportional to the absolute temperature divided by the pressure.
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Avogadro's Law
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Equal volume of any two gases at the same temperature and pressure contain the same number of molecules
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Molar gas volume
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Vm. The volume of one mole of gas
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Standard temperature and pressure
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Reference conditions for gases chosen by convention to be 0 degrees Celsius and pressure
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Avogadro's law on molar gas volume
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The molar gas volume at a given temp and pressure is a specific constant independent of the nature of the gas
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Ideal gas equation
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V= constant x T/P
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Molar gas constant
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R. The constant of proportionality relating the molar volume of a gas to temp and pressure
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Ideal gas law
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Combination of the gas laws. Includes all the information contained in Boyle's, Charles's, and Avogadro's laws
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According to John Dalton
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Each gas in a mixture of unreactive gases act as though it were the only gas in the mixture.
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Ideal gas law equation
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PV=nRT
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Partial pressure
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The pressure exerted by a particular gas in a mixture
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Dalton's law of partial pressure
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The sum of the partial pressures of all the different gasses in a mixture is equal to the total pressure of the mixture
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Mole fraction
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A component gas is the fraction of moles of that component in the total miles of gas mixtures.
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Kinetic-Molecular theory
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A gas consists of molecules in constant rands motion
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Postulates
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The basic statements from which all conclusions of predictions of a theory are deduced
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Kinetic postulate 1
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Gases are composed of molecules whose size is negligible compared with the average distance between them
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Kinetic postulate 2
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Molecules move randomly in straight lines in all directions and at various speeds
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Kinetic postulate 3
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The forces of attraction or repulsion between two molecules in a gas are very weak or negligible, expect when they collide
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Kinetic postulate 4
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When molecules collide with one another, the collisions are elastic
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Elastic collision
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The total kinetic energy remains constant; no kinetic energy is lost
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Kinetic Postulate 5
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The average kinetic energy of a molecule is proportional to the absolute temperature
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According to the kinetic theory
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The pressure of a gas results from the bombardment of container walls by molecules
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According to the kinetic theory
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Pressure of gas will be proportional to the frequency of molecular collisions with a surface and to the average force exerted by a molecule in collision
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Speeds of molecules Ina gas vary over a range of values
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Speeds of molecules Ina gas vary over a range of values
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Root-mean- square molecular speed
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A type of average molecular speed, equal to the speed of a molecule having the average molecular kinetic energy
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Gaseous diffusion
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The precedes where by a gas spreads out through another gas to occupy the space uniformly.
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Effusion
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Process in which a gas flows through a small hole in a container
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Graham's law of effusion
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The rate of effusion of gas molecules from a particular hole is inversely proportional to the square root of the molecular mass of the gas at constant temperature and pressure
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Rate of effusion depend on 3 factors
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1. The cross-sectional area of the hole- larger the hole, more likely molecules are to escape
2. The number of molecules per unit volume- more crowded, more likely to encounter the hole
3. The average molecular speed- faster the molecules, the sooner they will escape
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Van set Waals equation
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An equation similar to the ideal gas law, but included two constants, a and b, to account for deviations from ideal behavior.
(P+ n2a/V2) (V-nb)= nRT
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Chemical bond
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A strong attractive force that exists between certain atoms in a substance
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Covalent bonding
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Two atoms share valence electrons, which are attracted to the positively charged cored of both atoms, thus linking them
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Metallic bonding
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Valence electrons move throughout the crystal. Attraction holds the crystal together
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Ionic bond
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A chemical bond formed by the electrostatic attraction between positive and negative ions.
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Cation
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Atom that loses electrons. Positive
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Anion
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Atom that gains electrons. Negative
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Lewis electron- for symbol
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A symbol in which the electrons in the valence she'll of an atom of ion are represented by dots places around the letter symbol of the element
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Ionic bonding steps
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1. an electron is transferred between the the two separate atoms to give ions
2. The ions then attract one another to form an ionic bond
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Coulomb's law
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Potential energy obtained in bringing two charges, Q1 and Q2, initially far apart, up to a distance(r) apart is directly proportional to the product of the charges and inversely proportional to the distance between them.
E= (kQ1Q2)/ r
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Lattice energy
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The change in energy that occurs when an ionic solid is separated into isolated ions in the gas phase
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Ionic bonding occurs
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Between a reactive metal and a reactive nonmetal
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Ionic substances are
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High melting solids
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Cations of group IA to IIIA having noble gas or pseudo noble gas configurations
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The ion charges equal the group numbers
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Cations of groups IIIA to VA having noble gas or pseudo noble gas configurations
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The ion charges equal the group numbers minus two
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Anions of groups VA to VIIA having noble gas or pseudo noble gas configurations
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The ion charges equal the group numbers minus eight
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Ionic radius
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A measure of the size of the spherical region around the nucleus of an ion within which the electrons are most likely to be found.
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Isoelectronic
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Refers to different species having the same number and configuration of electrons
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Lewis electron dot formula
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Formula using dogs to represent valence electrons
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Bonding pair
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An electron pair shared between two atoms
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Lone, or nonbonding, pair
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An electron pair that remains on one atom and is not shared
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Coordinate covalent bond
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A bond formed when both electrons of the bond are donated by one atom
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Octet rule
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The tendency of atoms in molecules to have eight electrons in their valence shells
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Single bond
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A covalent bond in which a single pair of electrons is shared by two atoms
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Double bond
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A covalent bond in which two pairs of electrons are shared by two atoms
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Triple bond
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A cone lent bond in which three pairs of electrons are shared by two electrons
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Polar covalent bond
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A covalent bond in which the bonding electrons spend more time best one atom than the other
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Electronegativity
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A measure of the ability of an atom in a molecule to draw bonding electrons to itself l
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Large electronegativity
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An atom that tends to pick up electrons easily and hold on to them strongly
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Small electronegativity
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An atom that tends to lose electrons readily and has little tendency to gain electrons
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Metals
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...
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Nonmetals
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Most electronegative
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Nonpolar
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Small electronegativity
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Polar
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Large electronegativity
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Delocalized bonding
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Type of bonding in which a bonding pair of electrons is spread over a number of atoms rather than localized between two
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Resonance description
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Describe the electron structure of a molecule having delocalized bonding by writing all possible electron dot formulas
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Exceptions to the octet rule
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1. A group of molecules with an atom having fewer than eight valence electrons around it
2. A group of molecules with an atom having more than eight valence electrons around it
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Formal charge
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Hypothetical charge you obtain by assuming that bonding electrons are equally shared between the bonded atoms and that the electrons of each line pair belong completely to one atom.
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Rules for formal charge
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1. 1/2 of the electrons of a bond are assigned to each atom in the bond
2. Both electrons of a line pair are assigned to the atom to which the lone pair belongs
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Rules for deciding which of several resonance formulas best approximates the electron distribution of a molecule or ion
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Rule A: whenever you can write several Lewis formulas for a molecule, choose the one having the lowest magnitudes of formal charges
Rule B: when two proposed Lewis formulas for a molecule have the same magnitudes of formal charges, choose the one having the negative formal charge in the more electronegative atom
Rule C: when possible, choose Lewis formulas that do not have like charges on adjacent atoms
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Bond length
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The distance between the nuclei in a bond.
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Covalent radius
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The value for the atom in a set of covalent radio assigned to atoms in such a way that the sum of the covalent radio of atoms A and B predicts the approximate A-B bond length
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Bond order
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The number of pairs of electrons in a bond
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Bond dissociation
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The energy required to break a particular bond in a molecule
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Bond enthalpy
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Can use as a measure of the average strength of a bond in its compound. The average enthalpy change for the breaking of an A-B bond in a molecule in the gas phase
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Molecular geometry
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The general shape of a molecule, as determined by the relative positions of the atomic nuclei
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