CHEM 107 Final Brown
f =
c / λ
chemical bonds =
(bonds broken cancel out) reactants - products
E =
(h x c)/wavelength
Under what conditions does the enthalpy change equal the heat of a process?
constant pressure
when l = 2
d
if a reaction gets hotter, the enthalpy:
decreases (negative)
ln k =
-Ea/RT + lnA
polar bond value
0<x<1.8
Maximum number of electrons in atoms in a given quantum number: n = 3 , l = 1, ml = -1, ms = -1/2
1 electron
Suppose that a 58.25-g block of nickel at 145°C is placed in a thermos bottle containing 125 g of water at 21.0°C. Assuming that no heat is lost to or gained from the surroundings, what will be the final temperature of the nickel and water?
1. Thermal energy gained by water = mass of water x specific heat of water x (final temperature - initial temperature)
given temps(K) and k(s^-1) determine Ea in kJ/mol
1. arrhenius equation: ln(k2/k2) = Ea/R(1/T1-1/T2) 2. plug in the numbers from the chart 3. solve for Ea
A sample of a smokestack emission was collected into a 1.25-L tank at 725mm Hg and analyzed. The analysis showed 92% CO2, 3.6% NO, 1.2% SO2, and 4.1% H2O by mass. What is the partial pressure exerted by each gas?
1. assume 100 g sample and use the percentage for each molecule's mass to find moles of each 2. calculate total moles by adding the moles of each molecule together 3. find mole fraction for each molecule and multiply each by the pressure 4. answer = pressure of each molecule
A calorimeter contained 75.0 g of water at 16.95 C. A 93.3-g sample of iron at 65.58 C was placed in it, giving a final temperature of 19.68 C for the system. Calculate the heat capacity of the calorimeter. Specific heats are 4.184 J/gC for H2O and .444 J/gC for Fe
1. determine the heat gained by the calorimeter 2. find the heat capacity of the calorimeter 1. heat lost(iron) = heat gained(water) = heat gained(calorimeter) specific heat x mass x T(iron) = specific heat x mass x T(water) + heat gained(calorimeter) 2. heat capacity(calorimeter) = heat gained(calorimeter) /T change in water C(calorimeter) = q/T
A sample containing only NO2 and SO2 has a total pressure of 120 torr. Measurements show that the partial pressure of NO2 is 43 torr. If the vessel has a volume of 800 mL and the temperature is 22 C, how many moles of each gas are present?
1. subract 23 torr from the total for SO2 2. find total temp (Kelvin) 3. use volume and R involving torr 4. n=PV/RT (calculate for each pressure)
What is the total pressure (in atm) of a 15-L container at 28C that contains 3.5 g of N2, 4.5 g of O2, and 13 g of Cl2?
1. use the total number of moles present 2. determine the moles of each gas 3. use ideal gas law to calculate pressure
When octane is combusted with inadequate oxygen, carbon monoxide may form. If 100 g of octane are burned in 200 g of O2, are conditions conducive to forming carbon monoxide?
1. write a balanced equation 2. stoichiometry calculation to determine if there is excess O2 (mol to mol ratio) 3. insufficient O2 present and CO will form 4. conditions are conductive
What volume of oxygen at 24 C and .88 atm is needed to completely react (combustion ) with 45 g of methane gas?
1. write the equation 2. determine moles of methane by dividing molar mass 3. relate moles of methane to O2 (mole to mole ratio) 4. use ideal gas law to calculate the volume O2
second order with graphs:
1/concentration v time = positive slope (k) linear
The following mechanism is proposed for a reaction: NO + Br2 = NOBr2 (slow) NOBr2 + NO = 2NOBr (fast) overall equation for reaction:
2NO + Br2 = 2NOBr
N2 + O2 = 2NO H = 180.5 kJ how much energy is required to generate 35 moles of NO
35 mol NO x (1 mol rxn/2 mol NO) x (180.5 kJ/ mol rxn) = 3200 kJ
A particular orbital has n = 4 and l =2. What type of orbital must this be? 3p, 4p, 5d, or 4d
4d
What is the maximum number of 3d orbitals that could be present in any one atom?
5
Maximum number of electrons in atoms in a given quantum number: n= 3 , l = 1
6 electrons
Generally, an excess of O2 is needed for the reaction Sn+O2=SnO2. What is the minimum number of moles of oxygen required to oxidize 7.3 moles of tin?
7.3 moles of O2 is minimum moles of oxygen tin is limiting
Maximum number of electrons in atoms in a given quantum number: n = 2
8 electrons
XeF4 bond angles
90
What type of atom is needed as a dopant in a p-type semiconductor? Why is it called p-type?
A semiconductor is named p-type because a dopant creates "positive" holes in the valence band. To do this, the dopant must have fewer valence electrons than the atom that is replaced.
k =
Ae^(-Ea/RT)
When a reaction is exothermic, how does that influence S of the system? Of the surroundings?
An exothermic reaction releases heat. This process has no significant effect on the entropy of the system. The heat released is absorbed by the surroundings, which increases the molecular motion and randomness of the surroundings. This will have a very significant effect (increase) on the entropy of the surroundings.
pressure and LeChatelier's principle:
An increase in pressure causes the gas molecules to be colliding more often. LeChatelier's principle states that the system will try to "undo" the change we've made. The system does this by shifting the equilibrium to favor the reaction where fewer gas molecules are produced, thus causing molecules to collide less often
The following mechanism is proposed for a reaction: NO + Br2 = NOBr2 (slow) NOBr2 + NO = 2NOBr (fast) intermediate:
An intermediate is a substance in the mechanism that is neither a product nor a reactant. It forms in one step but is consumed in a later step; therefore it does not appear in the overall reaction. NOBr2 is an intermediate in this mechanism.
Describe the differences between a covalent bond and an ionic bond.
An ionic bond is the electrostatic force of attraction between oppositely charged ions. A covalent bond is a force of attraction between neutral atoms that occurs when the two atoms share a pair of electrons in overlapping atomic orbitals. The main difference is the extent to which electrons are shared versus transferred between the two bonding atoms.
metals tend to form:
cations
For the reaction, PCl5(g) = PCl3 +Cl2(g) , the measured equilibrium constant is 7.7 x 10^-3 at 25 C. (a) Based on this information, predict if G is positive or negative. Explain your answer.
Because the value of K is less than 1, it suggests that equilibrium lies toward reactants, and therefore G should be a positive number
Define the term calorimetry.
Calorimetry is the science of measuring heat flow. It is the primary way that we determine changes in the energy of systems.
For green light with a wavelength of 532 nm, what is the minimum number of photons the eye could detect?
E = hc/ wavelength
Distinguish between electron affinity and electronegativity.
Electron affinity is defined as the energy change associated with the addition of an electron. It is related to formation of anions. Electronegativity is a property measuring the ability of an atom to attract electrons to it when the atom is involved in a bond.
According to the second law of thermodynamics, how does the sign of S(u) relate to the concept that some energy is "wasted" or lost to the surroundings when we attempt to convert heat into work?
Entropy changes can be defined as heat flow at constant temperature. By converting heat to work, the temperature of the system is lowered, resulting in a decrease in the entropy of the system. The entropy change of the universe must be positive, so the entropy change of the surroundings must be larger than the absolute value of the entropy change of the system and have a positive value. So heat must be lost from the system to the surroundings, S(surr) = q(surr)/T
sigma and pi bonds
Every single covalent bond is a sigma bond. Every double covalent bond has both a sigma and a pi bond in it. Every triple covalent bond has a sigma and two pi bonds in it.
Order with respect to each reactant and overall order: A + B + C = D + E rate = k[A][B]^2
First order with respect to A, second order with respect to B, zero order with respect to C, and third order overall.
If 14.8 kJ of heat are given off when 1.6 g of HCl condenses from vapor liquid, what is H(cond) for this substance?
H(cond) is the heatflow per mole of HCl condensing: H = q/mol HCl
combustion reaction products:
H2O and CO2
Under what conditions do the postulates of the kinetic theory break down?
High pressure and/or low temperature
band diagrams: insulators:
completely separated
band diagrams: metals
completely together
Covalently bonded compounds tend to have much lower melting and boiling points than ionic compounds. How can the differences between ionic and covalent bonding explain this observation?
In a covalently bonded compound, strong bonds hold the atoms together in molecules, and the forces between molecules are much weaker. Only those weaker intermolecular forces need to be overcome to melt or boil the substance. In ionic compounds, discrete molecules do not exist. The strong Coulombic interactions between ions extend throughout the crystal, leading to high melting and boiling points.
Coulombic forces are often used to explain ionic bonding. Are coulombic forces involved in covalent bonding as well? Explain.
In a different way, negatively charged electrons in the bond are attracted to the positively charged protons in both nuclei, creating coulombic forces.
What is the difference between homogeneous equilibrium and heterogeneous equilibrium?
In a homogeneous equilibrium all species are in the same phase. This is not the case in a heterogeneous equilibrium.
second order units:
L/mol*s
first order with graphs:
concentration v time is not linear (exponential looking) negative slope ln(concentration) v time slope = -k
The following mechanism is proposed for a reaction: NO + Br2 = NOBr2 (slow) NOBr2 + NO = 2NOBr (fast) molecularity:
Molecularity refers to the number of molecules involved in the mechanism step and indicates the order of that step. Steps one and two are both bimolecular.
the element X in a trigonal bipyramidal compound with the formula XCl5?
P, As
P1V1 =
P2V2
P1V1/T1 =
P2V2/T2
For the reaction, PCl5(g) = PCl3 +Cl2(g) , the measured equilibrium constant is 7.7 x 10^-3 at 25 C. calculate G
T = 289 G = -RT(lnK) 12kJ/mol
What type of molecular shape?: IF3
T-shape
Keq =
[C]^x[D]^x/[A]^x[B]^x
first law of thermodynamics:
The law which states that the total energy of a system and its surroundings remain constant The change in the energy of a system equals the heat flow in the system from the surroundings minus the work done by the system on the surroundings
Explain why the s block of the periodic table contains two columns, the p block contains six columns, and the d block contains ten columns.
The number of columns in each block matches the number of electrons that can be accommodated in the corresponding subshell. An s subshell consists of just 1 orbital, so it can hold 2 electrons. A p subshell contains 3 orbitals, so it can hold up to 6 electrons. A dsubshell has 5 orbitals, and can hold 10 electrons.
Ammonia can react with oxygen to produce nitric oxide and water. 4NH3(g) + 5O2(g) = 4NO(g) + 6H2O(g) If the rate at which ammonia is consumed in a laboratory experiment is 4.23x10^-4 mol/L/S, at what rate is oxygen consumed? At what rate is NO produced? At what rate is water vapor produced?
The rate of consumption of NH3 is related to the rates of the other substances in the equation through stoichoimetry: the molar ratios. Recall that the rate of consumption of a reactant is negative and the rate of formation of a product is positive. 4.23 X 10^-4 x 5 mol O2/ 4 mole NH3 etc
A reaction has the experimental rate equation rate = k[A]^2. How will the rate change if the concentration of A is tripled? If the concentration of A is halved?
The rate will increase by a factor of 9 if [A] is tripled. The rate will decrease by a factor of 4 if [A] is halved.
Why do we need to consider the surroundings of a system when applying the second law of thermodynamics?
The second law of thermodynamics states that the total entropy change of a spontaneous process is always positive. The universe is the sum of the system and the surroundings; therefore, the surroundings must be considered.
The following mechanism is proposed for a reaction: NO + Br2 = NOBr2 (slow) NOBr2 + NO = 2NOBr (fast) rate determining step:
The slowest step in the mechanism is the rate-determining step. This is the first step in this mechanism: (first reaction)
In the reaction of arsenic with bromine, will form only when excess bromine is present. Write a balanced chemical equation for this reaction. Determine the minimum number of moles of bromine that are needed if 9.6 moles of arsenic are present.
The two reactants are arsenic, As, and bromine, Br2. The balanced equation is: 2As + 5Br2 = 2AsBr5 We need to do a stoichiometry calculation to determine the minimum number of moles required to react with 9.6 moles As. 9.6 mol As x 5 mol Br2/2 mol As = 24 mol Br2 required to react with all the There must be at least 24 moles Br2.
EQ EQUATION A system of mole of oxygen gas, O2(g) , is placed in a closed 1.00-L container and is brought to equilibrium at 600 K. O2(g) = 2O K = 2.8 x 10^-39 What are the equilibrium concentrations of O and O2?
This is a basic equilibrium problem: given the K and initial amounts, solve for the equilibrium amounts. A three-step approach is useful for these. 1. fill out ice table 2. write the eq constant expression set to K 3. substitute eq concentrations in terms of X into this equation and solve for X 4. plug X in for O and O2 concentrations
The decomposition of N2O5 in solution in carbon tetrachloride is a first-order reaction: 2N2O5 = 4NO2 + O2 The rate constant at a given temperature is found to be 5.25 x 10^-4. If the initial concentration of N2O5 is .200 M, what is its concentration after 10 minutes have passed?
This is an integrated rate law problem where we are given the elapsed time and must solve for the final amount of reactant. The first-order integrated rate equation is: ln[x]t/[x]0 = -kt or [x]t = [x]0e^(-kt) [x]t=final concentration [x]0 = initial concentration t = time elapsed k = rate constant [N2O5] is unknown [N2O5] = .200(e^(-5.25x10^-4 x 600) = .15 M
A group of students working on chemistry homework calculates the equilibrium constants for three reactions. Reaction 1 has G =-50kJ, reaction 2 has G =-30kJ. The students are surprised when their answers for each reaction are very close to K=1. Suggest what error the students must have made and calculate the actual values of K for these reactions.
This was probably an error in units. The value for R is in J and the G value is in kJ. If the numbers obtained for G are converted to J, the differences among the reactions become more obvious. The correct K values are 5.8x10^8, 1.8x10^5, and 57, respectively.
When you buy a Mylar™ balloon in the winter months in colder places, the shopkeeper will often tell you not to worry about it losing shape when you take it home (outside), because it will return to shape once inside. What behavior of gases is responsible for this advice?
Volume and absolute temperature are directly related when moles of gas and pressure remain constant. This relationship is known as Charles's Law. When the balloon is taken outside in the winter, the temperature of the gas decreases and so the volume of the balloon decreases as well. When the balloon is returned to room temperature, however, the balloon returns to its original size.
what do nonmetals tend to form:
anions
λ=
c / f
molecules to moles:
divide by Avagadro's number
when finding the largest electronegativity:
don't consider the noble gases (8th row)
0 order =
doubling concentration and nothing happens
when l = 3
f
E =
hv
BE + KE =
hv = E photon
How many of the following statements are true? (i) A material with a large band gap will act as an electrical insulator. (ii) Doping silicon with phosphorus produces a p-type semiconductor. (iii) The conductivity of pure silicon increases at higher temperatures. (iv) The conduction band lies at higher energies than the valence band.
i, ii, iv
state function:
internal energy, enthalpy, and entropy are state quantities because they describe quantitatively an equilibrium state of a thermodynamic system, irrespective of how the system arrived in that state.
how to determine paramagnetism:
it has unpaired electrons
HCl and CaCl2 are both strong electrolytes. Suppose 125 mL of 0.120 M HCl and 250 mL of 0.240 M CaCl2 are mixed. Assuming a final volume of 375 mL, what is the concentration of Cl- ions in the resulting solution?
just add the molarities together (.360 M)
using arrhenius expression determine highest activation energy:
largest exponent
using arrhenius expression determine which reaction is fastest:
largest number in chart
huge Keq =
lots of product and not much reactant
Kinetic energy is proportional to temperature, so:
molecules with smaller mass have the faster molecular speed at constant temperature
entropy: more moles =
more entropy
at higher temps:
more molecules will move with higher speeds needed to produce reactive collisions
n-type band diagrams:
more negative (more black)
moles to grams:
multiply by molar mass
q =
nCΔT mCΔT
PV =
nRT
when l = 1
p
ΔG, ΔH, ΔS =
products-reactants
A metal radiator is made from 26.0 kg of iron. The specific heat of iron is 0.449 J/gC. How much heat must be supplied to the radiator to raise its temperature from 25.0 to 55.0 C?
q = mcT q = (mass, g)(specific heat, J/gC)(temperature change, C) m = 26.0 kg = 26,000 g q = (26000g)(0.449J/gC)(55.0-25.0 C) = 3.5 x 10^5
heat balance:
q(cold) = -q(hot)
A = B+C :
rate = k[A]
A+B = C+D
rate = k[A][B]
The following mechanism is proposed for a reaction: NO + Br2 = NOBr2 (slow) NOBr2 + NO = 2NOBr (fast) rate expression for each step:
rate1 = k1[NO][Br2] rate2 = k2[NOBr2][NO]
chapter 1 equations to know:
relationships between moles, mass, volume, etc. Stoichiometry
when l = 0
s
SeF4 molecular geometry:
seesaw
What type of molecular shape?: TeF4
seesaw
The following reaction is in equilibrium in lake water: HCO3(aq) + H(aq) = H2CO3 Predict the change in the reaction quotient, Q, for each disturbance below, and use that prediction to explain how the equilibrium is shifted by the stress. b) H2CO3 is added:
shift to the left
The following reaction is in equilibrium in lake water: HCO3(aq) + H(aq) = H2CO3 Predict the change in the reaction quotient, Q, for each disturbance below, and use that prediction to explain how the equilibrium is shifted by the stress. c) NaOH is added
shift to the left
The following reaction is in equilibrium in lake water: HCO3(aq) + H(aq) = H2CO3 Predict the change in the reaction quotient, Q, for each disturbance below, and use that prediction to explain how the equilibrium is shifted by the stress. a) NaHCO3 is added to the lake:
shifts to the right
at lower temps:
slower molecular speeds
using arrhenius expression determine the lowest activation energy:
smallest exponent in chart
hybrid orbitals: single bonds double bonds triple bonds
sp, sp2, sp3 sp, sp2 sp
hybridization of GeF4
sp3
What type of molecular shape?: XeO4
tetrahedral
ionization energy definition:
the minimum amount of energy required to remove an electron from the neutral atom and form a cation
smaller K value =
the more reverse reaction is favored
zero order with graphs:
the slope of the line is -k concentration v time = linear
What type of molecular shape?: ClO3-
trigonal pyramid
covalent/non-polar bond value
x = 0
The hypothetical reaction, A+B=C, has the rate law Rate = k[A]^x[ B]^y When [A] is doubled and [B] is held constant, the rate doubles. But the rate increases fourfold when [B] is doubled and [A] is held constant. What are the values of x and y?
x = 1 y = 2
ionic bond value
x>= 2
ΔG =
ΔH - TΔS
rate =
Δ[A]/ ΔT
c =
λv
