Final Review - Chem 31A
Terms in this set (185)
6.02 x 10^23
What is the mass of a neutron?
How much is 1 amu?
Ideal Gas Law
Real gas deviates at low temps and high pressures; also, its particles exert forces on each other (intermolecular forces)
Difference between ideal gas and real gas
a property of matter representing the mass per unit volume;
Density = molar mass/ molar volume
ideal molar volume = 22.4 L
Density of gas under ideal conditions
Kinetic Molar Theory of Gases
a model used to explain the behavior of gases
1. The size of a particle is negligibly small
2. The average kinetic energy of a particle is proportional to the temperature in kelvins
3. The collision of one particle (or with the walls) is completely elastic
**In a gas mixture at a given temperature, lighter particles travel faster (on average) than heavier ones
root mean square velocity
square root of the average of the squares of the particle velocities
Average KE of a gas
KE = 1/2mv² = 3/2(kB)
w = -P∆V
What is the equation for work?
∆H = ∆E + P∆V = q (at constant pressure)
∆H = ∆E (at constant volume)
What is the equation for enthalpy
heat of products-heat of reactants=heat of reation
A reaction that ABSORBS energy in the form of heat
A reaction that releases energy in the form of heat
q = mC∆T
heat transfer (no phase change)
q = C∆T
equation for heat of a system when heat capacity is given (used in calorimetry)
q = n∆H
Equation of heat of reaction in J/mol when given ∆Hrxn and number of moles of reaction
Pauli exclusion principle
An atomic orbital may describe at most two electrons, each with opposite spin direction
* Fill in each box once, then start filling in the next one. Sub level orbitals are singly occupied as far as possible.
decreases as you move down a group (elements are getting larger/ electrons are held less tightly to nucleus), increases as you go across a period (electrons are held closer to nucleus)
Trends in Ionization Energy
decreases as you go down a group, increases as you go across a period
decreases as you go down a group, increases as you go across a period
A measure of the ability of an atom in a chemical compound to attract electrons
A bond formed when atoms share one or more pairs of electrons
bonding with uneven electrons
a covalent bond in which electrons are shared equally by both atoms
Formed when one or more electrons are transferred from one atom to another
the chemical bonding that results from the attraction between metal atoms and the surrounding sea of electrons
a molecular geometry in which all atoms line up along a straight line
180 degree bond angle
2 electron groups; 2 bonding; 0 lone pairs
Also: 5 groups; 2 bonding, 3 LP; sp3d
trigonal planar geometry
three electron groups
3 atoms 0 LP
nonlinear molecular geometry, in the case of a molecule of three atoms
2 atoms 1 LP = <120 degrees
4 atoms; 2 bonding; 2 LP = <109.5 degrees
4 bonds, 109.5 (sp3)
3 bonds, 1 lone pair
5 electron pair
lone pairs will line up in equatorial positions (position where groups are 120º apart)
90, 120 degree angles
Bond angle: 120 degree equatorial & 90 axial
the molecular geometry of a molecule with trigonal bipyramidal electron geometry and one lone pair in an equatorial position
Bond angle: <90 degree
the molecular geometry of a molecule with trigonal bipyramidal electron geometry and two lone pairs in an equatorial position
5 bonds, 1 lone pair, about 90 bond angle, AB5E typ
4 bonds, 2 lone pairs
Structures that occur when it is possible to draw two or more valid electron dot structures that have the same number of electron pairs for a molecule or ion
representations of bonding in molecules or ions when a single Lewis structure fails to describe accurately the actual electronic structure
Found in molecules containing triple bonds and single bonds. 180° bond angle. Composed of one s-orbital and one p-orbital.
An "S" orbital merges with two "P" orbitals to form three SP2 hybrid orbitals plus a leftover "P."
Used for double bonds
Ion ion attraction (strongest), hydrogen bonding, dipole dipole, dispersion (weakest)
4 types of Intermolecular Forces
Dissolving, the state of having been dissolved; breaking bonds
When compounds dissolve in water and break up into ions
very week attractions between non polar molecules
dipole dipole forces
attractions between oppositely charged regions of polar molecules
type of molecular attraction in which a hydrogen atom covalently bonded to an electronegative atom (e.g., O, N, F) in one molecule is attracted to an electronegative atom in a different molecule or in another part of the same molecule
compounds do not interact with water
are soluble in water. they dissolve in water (salt, sugar)
An equation that displays the exponential relationship between vapor pressure and temperature
ln(P2/P1) = -Hvap/R(1/T2-1/T1)
A liquid's resistance to flowing
Solid to liquid
Liquid to solid
Gas to solid
Solid to gas
Liquid to gas
Gas to liquid
A measure of how difficult it is to stretch or break the surface of a liquid
the temperature at which a liquid's vapor pressure reaches the external pressure
normal boiling point
the boiling point of a liquid at a pressure of 101.3 kPa or 1 atm
The line that indicates the interface between liquid and solid. Melting point can also be found along this line.
A line (set of ordered pairs of critical temperature and critical pressure) that represents the equilibrium between a solid and a gas
A line (set of ordered pairs of temperature and pressure) on which each point is the boiling point of the substance at that pressure
the temperature and pressure conditions at which the solid, liquid, and gaseous phases of a substance coexist at equilibrium
the temperature and pressure at which the gas and liquid states of a substance become identical and form one phase
Any substance at a temperature and pressure above its critical point, where distinct liquid and gas phases do not exist
1. water exists in three states 2. it has very high heat capacity 3. water is an extremely strong solvent 4. it undergoes unusual variations in density and temp change and ice(solid water) has a lower density than liquid water
unusual properties of water
light and/or gas emitted, temperature change, color change, precipitate forms, electrical potential
Evidence of a chemical change
color change, gas, water is a new product
The separation of ZnL2 back into its constituent elements through electrolysis is an ______
The Law of conservation of mass
Chemical equations must be balanced to satisfy
In a chemical reaction, matter is not created or destroyed, but is conserved
Law of Definite Proportions
a given compound always contains exactly the same proportion of elements by mass
Law of Multiple Proportions
whenever two elements form more than one compound, the different masses of one element that combine with the same mass of the other element are in the ratio of small whole numbers
1.602 x 10^-19 C
Charge of Proton in Coulombs
-1.602 x 10^-19 C
Charge of Electron in Coulombs
Charge of Neutron in Coulombs
mass of proton/ neutron
9.109 x 10^-31 kg
mass of electron
What is the symbol for the atom or ion that contains 9 protons, 10 neutrons and 10 electrons?
12C has a mass of 12.0000amu and a natural abundance of 98.892%
13C has a mass of 13.003amu and a natural abundance of 1.108%
What would be the most likely mass of a carbon atom selected at random?
(1) 12.0000 amu
(2) Slightly more than 12.0000amu
(3) Slightly less than 12.0000 amu
(4) 13.003 amu
(5) Slightly less than 13.003 amu
What is the mass of 2.0 moles carbon atoms in atomic mass units?
a) 24 amu
b) 1.2*1024 amu
c) 1.4*1025 amu
d) 3.3*10-24 amu
e) 4.0*10-23 amu
Compared to 2.0g of I2, 2.0 g of Zn will:
a) Contain more atoms of Zn than atoms of I
b) Contain fewer atoms of Zn than atoms of I
c) Contain the same number of atoms
What is the empirical formula of the compound of nitrogen and oxygen which is 47% nitrogen by mass?
a chemical reaction that occurs when a substance reacts with oxygen, releasing energy in the form of heat and light
A reaction in which oxygen reacts with another substance to produce carbon dioxide and water
With 100 moles of hydrogen and 100 moles
of oxygen, how many moles of water can be produced in the reaction?
2 H2(g) + O2(g) → 2H2O(g)
(A) 100 moles
(B) 200 moles
(C) 50 moles
(D) 25 moles
A gas that follows the gas laws at all conditions of pressure and temperature
what is an ideal gas?
Equal volumes of gases at the same temperature and pressure contain equal numbers of particles
The density of Hg is 13.6 g/cm3. The density of water is 1.0 g/cm3. If we were to make a barometer out of water, how tall would the
glass tube need to be?
A. 0.760 meters.
B. About 5 meters.
C. About 10 meters.
D. About 20 meters.
E. You are kidding me; not enough information to guess.
Lake Lagunita at Stanford is about 10 m deep in the winter during the rainy season. What is the pressure at the bottom of the lake?
A. About 1 Atm
B. About 2 Atm
C. About 0 Atm
D. Not enough information. It depends on the area of the lake.
Clicker: Which of the following samples would have the largest volume at 25oC and 750mmHg?
(1) 100g CO2
(2) 100g CH4
(3) 100g NO
(4) 100g SO2
(5) All volumes would be the same
Identify an unknown gas
• 1.32g of an unknown gas occupies 0.8206L at 760.mmHg and 27°C.
• Identify the unknown gas.
Dalton's Law of Partial pressure
the total pressure exerted by the sum of the partial pressure of the gases present.
Why are runners who train at sea level disadvantaged when they
run a marathon in Denver (most important reason)?
A. The mountain air freaks them out.
B. The air is drier and they dehydrate more quickly.
C. There is less oxygen in the air in Denver.
D. The fans in Denver are not very polite.
E. The air is thinner and there is less wind resistance.
There is 0 motion of particles
The coldest temperature, 0 Kelvin, that can be reached. It is the hypothetical temperature at which all molecular motion stops.
1. Increase number of atoms (more collisions)
2.Increase frequency of collisions
3. Increase Momentum
How to increase pressure of a gas (Kinetic Theory of Gases)
a measure of the kinetic energy of molecules
Maxwell-Boltzmann Velocity Distribution
A a given temperature, some molecules move fast, some average, some slow
As T increases, peak of distribution moves to higher velocity and width of distribution increases
decreasing molar mass
Average kinetic energy increases with _____________
Graham's Law of Effusion
the rate of effusion of a gas is inversely proportional to the square root of the mass of its particles
rateA/rateB = sqrt(massB/massA)
A process by which gas particles pass through a tiny opening
The four most common gases in the atmosphere are N2, O2, Ar, and CO2. Which gas has the highest average kinetic energy at room temperature?
E) All have the same average kinetic energy
If held at the same temperature, a mole of Argon gas molecules versus a mole of Helium molecules will
2) Havethesame<Vx>,but Ar will have a greater <KE>
3) Have the same <Vx> , but Ar will have a smaller <KE>
4) Have the same <KE>, but Ar will have a smaller <Vx>
van der Waals equation
a mathematical expression for describing the behavior of real gases
For which system is the change in energy negative?
A) An ice cube (the system) melts and the surrounding beverage cools
B) A metal cylinder (system) is rolled up a ramp; assume there is no friction
C) Some steam (the system) condenses on skin, causing a burn.
D) All of these have a positive DE
E) All of these have a negative DE
∆E = q + w
Equation for ∆E
The plunger on a syringe of gas that was
previously compressed to 2atm absolute pressure is released. Which is true?
(1)The energy of the gas in the syringe is conserved: DEsys = 0
(2)The energy of the surroundings is conserved: DEsur = 0
(3)The gas in the syringe does work on the atmosphere: w < 0
(4)Work is done by the atmosphere on the gas in the syringe: w > 0
If the following reaction is run at
100oC and 1 atm, work, w, will be: 2 H2(g) + O2(g) → 2 H2O(g)
1. < 0
2. = 0
3. > 0
The reaction below is
O (g)+ O(g) → O2 (g).
2.No heat will be generated or adsorbed
4.Not enough information
forming bonds from atoms
Heat is released in a reaction when _______
Heat is absorbed in a reaction to __________
The enthalpy change for the reaction: 2 H2(g) + O2(g) → 2 H2O(g)
is -484kJ/mol at 100oC and 1atm.
What is q, if 1mol H2(g) is consumed by this reaction at constant pressure and temperature?
The amount of energy required to raise the temperature of 1 gram of a substance by 1 degree Celsius
Assuming this temperature increase has been constant, how much heat has been absorbed by the world's oceans over the last 3 decades?
If 1mol H2O(l) at 10oC is placed in contact with 1mol Hg(l) at 50oC, the final temperature is:
Which statement is true?
A) All dissolution reactions are exothermic because they occur spontaneously
B) All dissolution reactions are endothermic because it requires energy to break apart the bonds within the solid
C)Dissolution reactions could be endo or exothermic depending upon the bonds that form in solution
D)Dissolution reactions will only be exothermic if the solid dissociates into ions
Constant pressure calorimetry
measures q at fixed P (∆H = q)
What is the sign of DT we would measure for an endothermic reaction in a calorimeter?
C. It depends on how big the calorimeter is.
Constant bomb calorimeter
done in a bomb calorimeter
Calculate the change in internal energy (ΔE) for a system that is absorbing 35.8 kJ of heat and is expanding from 8.00 to 24.0 L in volume at 1.00 atm. (Remember that 101.3 J = 1 L∙atm)
A) +51.8 kJ
B) -15.8 kJ
C) -16.6 kJ
D) -29.3 kJ
E) +34.2 kJ
Enthalpy of formation
When one mole of a compound is made from its elements (when written kJ/per mole of product)
Which reaction would not describe a heat of formation for the product?
A)MgO(s) + CO2(g)MgCO3(s)
B) Mg(s) + 1⁄2 O2(g) MgO(s)
C)C(s) +O2(g)CO2(g) D)Mg(s)+C(s)+ 3/2O2(g)MgCO3(s
E) All are heats of formation
Calculate the heat of combustion of methanol, ∆Ho, CH3OH(g) + 3/2 O2(g)CO2(g) + 2 H2O(g)
Which of the following statements are false?
A) If a chemical equation is multiplied by some factor,
ΔH°rxn is also multiplied by the same factor.
B) If a chemical reaction changes direction, then ΔH°rxn changes sign.
C) If a chemical equation can be expressed as the sum of a series of steps, ΔH°rxn for the overall equation is the sum of the heats of reactions for each step.
D) When writing heats of formation, standard states are all in the gas phase.
E) None of these statements are false
As particles and waves
How do light and electrons behave?
How do we know that light can behave like a particle?
B. Light bends in water
C. Einstein's interpretation of photoelectric effect
D. Maxwell's electromagnetic theory
Principle Quantum number
symbolized by n, indicates the main energy level occupied by the electron
angular moment of electron
spin quantum number
The quantum number that has only two possible values, +1/2 and -1/2, which indicate the two fundamental spin states of an electron in an orbital
orientation of electron
m, integers from -l to +l
Which electron in a neutral multi-electron atom would be expected to have the lowest ionization energy?
1) A 2p electron
2) A 2s electron
3) A 3d electron
4) A 3p electron
Higher lever atomic orbitals having significant amounts of probability within space occupied by orbital shaving significant amounts of probability working the space occupied by orbitals of lower energy level
The repulsion between electrons in different inner shells
the reduction of the attractive force between a positively charged nucleus and its outermost electrons due to the cancellation of some of the positive charge by the negative charges of the inner electrons
effective nuclear charge
the net positive charge experienced by an electron in a many-electron atom; this charge is not the full nuclear charge because there is some shielding of the nucleus by the other electrons in the atom
Based on periodic trends, what is the most likely compound of barium and chlorine
Decreases as you go right due to increasing nuclear charge
increases going down due to added energy levels
Atomic radii periodic trend
Boron. It has an electron in the 2p orbital, which is higher in energy than Be's s orbitals
Is it easier to move an electron from B than Be
Easier to remove one from oxygen, since oxygen has two paired electrons
It is easier to remove an electron from O than N? Why?
A particle of electromagnetic radiation with no mass that carries a quantum of energy
If the following reaction is run at
100oC and 1 atm, work, w, will be: 2 H2(g) + O2(g) → 2 H2O(g)
1. < 0 (work done by the system)
2. = 0 (no work will be done)
3. > 0 (work done on the system)
Chemical bonds form because they lower the potential energy between the charged particles that compose atoms.
Why does bonding occur?
Tro defines electronegativity to be the ability of an atom to attract electrons to itself within a chemical bond. Based on your knowledge of ionization energies, which element would have the greatest electronegativity?
the energy released when one mole of an ionic crystalline compound is formed from gaseous ions
Which lattice has the most negative lattice energy or is the most stable?
4) They are all approximately equivalent
FC = #valence - #nonbonding - #bonds
1. Maximize octet
2. minimize formal charge
3. negative charge should be on most electronegative atoms
4. non-zero charge on adjacent atoms should be opposite
What makes a good Lewis Dot Structure?
How many equivalent Lewis structures are there for the nitrate ion, NO3-?
Which of the following molecules canNOT satisfy the octet rule?
1. odd number of available valence electrons
2. too few electrons
3. too many electrons
Exceptions to the Octet rule
Consider the molecules NO+, NO3-, and HNO. Which has the shortest NO bond?
A) They are all equivalent
Which element will combine with sulfur to form a linear molecule with the formula XS2?
PC = #valence - #nonbonding - [ENa/(ENa + ENb)]xshared e-
In which molecule would you expect hydrogen to have the most negative partial charge?
5) Hydrogen will never have a negative partial charge
Which molecule would you predict to be polar? (i.e. has a net dipole moment)
Which molecule would you predict to be polar?
Which molecule would you predict to be polar?
(5) none of these
Valence Bond Theory
Valence bond theory describes the formation of bond in a molecule. It states that partially-filled atomic orbitals of different atoms overlap with each other in order to form covalent bonds.
Molecular Orbital theory
Suggests that the orbitals of a molecule's atoms are replaced by totally new orbitals when a molecule forms
Draw the Lewis structure for the molecule CH2CHCH3. How many sigma and pi bonds does it contain?
A) 8 sigma, 1 pi
B) 9 sigma, 0 pi
C) 9 sigma, 1 pi
D) 7 sigma, 2 pi E) 8 sigma, 2 pi
What happens to the vapor pressure of water when it's surface area is increased at constant T?
A. The vapor pressure increases
B. The vapor pressure stays the same
C. The vapor pressure decreases
D. It depends on the heat of vaporization
Increase temperature or pressure
How to increase vapor pressure?
Increasing the external pressure on a liquid will do which of the following:
A) increase the boiling point, but not affect the vapor pressure
B) Decrease the boiling point
C) increase the vapor pressure, therefore increasing the boiling point
D) decrease the amount of heat required to boil a mole of the liquid
E) B and D are true
Which halogen has the highest boiling point?
D. They will all be about the same since they are all diatomic
Clicker: Which molecule(s) will have dipole-dipole interactions present?
D) Both A and B
E) None of these
Suppose that 0.48g of water vapor at 25oC condenses on the surface of a 55g block of aluminum that is initially at 25oC.
Will the temperature of the block:
A) Increase from the water condensing on it
B) Decrease as the water condenses and cools it
C) Stay the same because they are both at the same temperature
The phase of a matter is determined by intermolecular forces, the average kinetic energy of the molecules in the matter (or T ) and P
What determines the phases of a substance?
In most substances, which tends to be greater - the heat of fusion or the heat of vaporization?
a) Heat of vaporization
b) Heat of fusion
c) They are both fairly similar
d) It's really random so there is no real trend
At a pressure of 10 atm, the melting point of ice is
A. Slightly above 0.oC.
B. Slightly below 0.oC.
At and near the triple point of the phase diagram of a substance:
A. The solid, liquid and gas phases of the substance can coexist in thermodynamic equilibrium.
B. Sublimation is likely to occur.
C. At that point, it is possible to change all of the substance to solid, liquid, or gas by making arbitrarily small changes in pressure and temperature.
D. All the above.
E. It is impossible to achieve an exact triple point
A hot air balloon rises because:
a) the pressure inside the balloon increases
b) the hot air in the balloon is less dense
c) the number of air molecules inside the balloon increases
d) all of the above
In which orbital below would an electron (on average) be closest to the nucleus?
Which electrons experience the greatest effective nuclear charge?
a) the valence electrons of Li
b) the valence electrons of Ne
c) the valence electrons of F
d) the valence electrons of N
Which statement is true of a reaction in which ∆V is positive?
A) ∆H = ∆E
b) ∆H > ∆E
c) ∆H < ∆E
d) depends on whether the reaction is exo or endothermic