Chemistry Test
What is the change in entropy for the reaction: H2(g) + Cl2(g)-> 2HCl(g) at 298K This process is?
+20.04J/K Favorable
What is the change in entropy for the reaction 3O2 → 2O3 at 298 K?
-138.0
Fe2O3(s) + 3CO(g) -> 2Fe(s) + 3CO2(g) Determine the standard Gibbs free energy and if it's spontaneous
-28.1kJ Yes, it's spontaneous
What is the enthalpy of formatin of Pb(NO3)2(s)?
-452.0
2H2(g) + O2(g)-> 2H2O(g) at 298K What is the standard change in Gibbs free energy? What are the conditions of this reaction?
-457.0 Favorable and spontaneous
Consider the reaction 4NH3+ 5O2 (g)-> 4NO (g) +6H2O (l). If the standard free energy of the reaction is -1.01x10^3kJ, then what is the Gibbs free energy of a reaction vessel containing 0.50atm NH3, 0.24 atm O2, and 1.3atm NO at 298K? Is it spontaneous?
-983kJ Yes, it is spontaneous
For the reaction A + 2B-> 3C, the rate of change of C is found to be 0.06 M/s. Find the rate of the reaction.
0.02
he rate constant for the following first-order reaction is 3.4 s: 2N2O(g)->2 N2(g) + O2(g) Calculate [N2O] in M that remains after 0.35 s if the initial concentration of N2O is 0.56 M
0.17 ln[A]= -3.4*0.35+ ln0.56
Consider the reaction A → B. Here, we have a 1:1 mole ratio of reactant-to-product. Suppose you start with 1.0 mole of A and the reaction commences. You observe that it takes 1.0 minute for 0.2 moles of A to be consumed. Hence, the rate of change of A over this time interval is (-0.2 moles)/(1.0 minute)= -0.2 moles/min In the same 1.0 minute period, how many moles of B formed?
0.2
Rank the following from least to greatest magnitude of entropy: C3H8(g), CH4(g), C4H10(g), C2H6(g)
1. CH4(g) 2. C2H6(g) 3. C3H8(g) 4. C4H10(g)
Rank the following from least to greatest magnitude of entropy CO2(s), CO2(g), CO2(l)
1. CO2(s) 2. CO2(l) 3. CO2(g)
Rank the rates of change in the reaction A + 2B->3C. Place the greatest rate of change at the top and the lowest at the bottom
1. Delta[C]/delta t 2. delta[B]/delta t 3. delta[A]/delta t
Rank the following species from least to greatest magnitude of entropy: H2(g), Cl2(g), N2(g), F2(g)
1. H2(g) 2. N2(g) 3. F2(g) 4. Cl2(g)
A zeroth order reaction A->B has [A] = 0.012 M. After 5.0 minutes had elapsed, [A] was found to be 0.0080 M. Determine the rate constant k in units of Ms
1.3x10^-5
A second order reaction has an initial reactant concentration of 0.032 M and a rate constant k of 1.4 M-1s-1. What will be the concentration of the reactant in M after 6.3 seconds of reaction?
1/0.025= 1.4t+ 1/0.032 0.025
A reaction rate is found to decrease by a factor of ¼ when a reactant's concentration is halved. What is the order with respect to this reactant?
2
In a zero order reaction, it takes 342 seconds for 75% of a hypothetical reactant to decompose. Determine the half life t1/2 in units of seconds.
227 [A]= -kt +[A]0 0.25=-k*342+1 k=0.0022-1 [A]0/2k 1/2(0.0022-1)
Consider the evaporation of bromine: Br2(l)-> Br2(g), where delta H= 30.9kJ/mol and delta S=102J/molK. At what temperature will this phase change become spontaneous?
303.0
If a system has 1x10^15 ways of arranging its energy, what will its entropy be?
4.77x10^-22J/molK
The reaction 2H2(g) + O2(g) → 2H2O(g) is used to fuel some liquid-propellant rockets. Although it has an unfavorable change in entropy (ΔS = −88.84 J/K), it is very exothermic, with a negative enthalpy of reaction (ΔH = −438.6 kJ). Below what temperature will this reaction be spontaneous? (Combustion reactions in rocket engines can reach around 3500 K.)
4962.0
What is the equilibrium constant of the reaction N2(g) + 3H2(g)-> 2NH3(g) if its standard free energy is -32.9kJ at 298K? Is it spontaneous? Which species are favored?
5.8x10^5 Yes it's spontaneous Products are favored
If a system has 100 ways of arranging its energy, what will its entropy be?
6.36x10^-23J/molK
Which chemical species would have the most microstates at the same temperature for a given measured macrostate?
A polyatomic gas like H2S
Positive entropy, negative enthalpy
Both favorable, all temperatures will be spontaneous
The entropy of an exothermic reaction increases. This reaction will be spontaneous under which of the following temperatures?
Both high and low temperatures
Negative entropy, positive enthalpy
Both unfavorable, no temperatures will be spontaneous
Which of the following atoms and compounds would you expect to have the most degrees of freedom (translational, rotational, plus vibrational modes)? Ar, O2, H2S, CH4
CH4
Macrostate
Collection of measured properties of the system
Enthalpy
Delta H= sum of products- sum of constituent elements Equal to the heat flow
Entropy
Distribution of energy in a system Increases as the number of microstates increases Associated with disorder
Gases and entropy
Don't have any restrictions on how they can distribute their energy, so gases have higher entropy than liquids or solids
What will happen to the rate if the concentration of A doubles
Doubles
Electrophiles
Electron deficient centers Accepts electrons
Nucleophiles
Electron rich centers Donates electrons
Activation
Energy difference between reactants and transition states Slower reaction has larger activation energy, while faster reactions have smaller activation energy
Intermeidate
Energy valley between the transition states Has a discrete lifetime
delta G= 0
Equilibrium Q=K Neither reactants nor products are favored
True or False: The following reaction is endothermic: 2 H(g) + O(g) → 2 HO(l)
False
Positive entropy, positive enthalpy
Favorable entropy, unfavorable enthalpy, high temperatures will be spontaneous
Exothermic Graph
Heat is given off, enthalpy
Concentration and rate of reaction
Higher concentration, faster the rate
Frequency of molecular collisions and rate of reaction
Higher frequency, faster rate By increasing the amount of reactant molecules, the frequency of collisions between A and B increases, resulting in a higher reaction rate Reaction rate is directly proportional to reactant concentration
Temperature and rate of reaction
Higher the temperature, faster the rate of reaction
Which molecule has the strongest london dispersion forces F, I, Cl, Br
I Larger molecules have larger london dispersion forces
Liquid and entropy
Liquids aren't held rigidly, which increases the degrees of freedom, have a greater entropy than solids
The catalyzed pathway in a reaction mechanism has _ activation energy which causes a _ reaction rate
Lower, faster
What are the units of k for a zeroth order reaction?
M/s
What are the units of k for a third order reaction?
M^-2s-1
Transition state
Maximum on an energy diagram
Degrees of freedom
Molecules have 3N total modes of motion, where N is the number of atoms in the compound
Write an equation for the enthalpy of formation of NaHCO3 (s). What are the correct constituent elements in NaHCO3(s)?
Na(s), H2(g), O2(g), C(s, graphite)
The entropy of an endothermic reaction decreases. This reaction will be spontaneous under which of the following temperatures?
Neither high nor low temperatures
Microstate
One possible arrangement of the energy in a system, which is whatever macroscopic object is made up of the molecules
The entropy of an endothermic reaction increases. This reaction will be spontaneous under which of the following temperatures?
Only high temperatures
The entropy of an exothermic reaction decreases. This reaction will be spontaneous under which of the following temperatures?
Only low temperatures
Endergonic
Positive delta G non-spontaneous forward reaction, reverse reaction is exergonic
Integrated Rate Law
Provide a quantitative relationship between reactant concentration and time
What will happen to the rate if the concentration of B doubles
Quadruples
What is the expression for the rate law for A+2B->C?
Rate= k[A]^x[B]^y
Zeroth Order Reaction
Rate=K[A]^0
Zeroth Order Reaction
Rate=K[A]^0 Units: M/s half life: [A]0/2k straight line: [A]t=-kt+[A]0
First Order Reaction
Rate=k[A]^1 units: s^-1 half life: ln2/k straight line: ln[A]= -kt+ ln[A0]
Second Order Reaction
Rate=k[A]^2 units: M^-1s^-1 half life: 1/k[A]0 straight line: 1/[At]= kt+ 1/[A]0
Thermodynamics
Relative energies of the reactants and products or the concentrations of reactants and products
Under standard conditions [A]= 1.0 M and [B]= 1.0 M, which reaction will have the greater rate?
Reverse reaction
Concentration time curve slope
Slope is steepest near start, so average reaction rate is fastest at 0
Which phase (solid, liquid, gas) has the lowest amount of entropy
Solids because atoms are held in a rigid crystalline arrangement, the kinetic energy of atoms in a solid is restricted mainly to vibration only, resulting in fewer degrees of freedom
Free energy of activation
Speed of a reaction on an energy diagram associated with the difference in energy between the reactants and the transition state
delta G< 0
Spontaneous forward reaction Q<K Products are favored
Chemical Kinetics
Study of reaction rate and factors affecting this rate
Catalyst
Substance that increases the rate of a chemical reaction by changing the reaction pathway without being changed itself at the end of the reaction, reduces the activation energy
Consider the combustion of propane: C3H8(g) + 5O2(g)->3CO2(g) + 4H2O(l). Which statement(s) is (are) true? -The rate of C3H8 consumption> the rate of CO2 production -The rate of H2O production< the rate of C3H8 consumption -The rate of CO2 production < the rate of H2O production -O2 will react the fastest out of all reactants and products
The rate of CO2 production< the rate of H2O production O2 will react teh fastest out of all reactants and products
Half life
Time required for the concentration of reactants to be reduced to 1/2 of its initial amount t1/2= [A]0/2k
Hammond Postulate
Transition state resembles structure of nearest stable species Exothermic/exergonic reaction, transitions state resembles the reactants Endothermic/ endergonic transition state resembles the products
True or False? The standard enthalpy of formation of any element in its standard state is always zero.
True
Negative entropy, negative enthalpy
Unfavorable entropy, favorable enthalpy, low temperatures will be spontaneous
The Gibbs free energy for a specific reaction is -400kJ, is the reaction spontaneous under the conditions calculated?
Yes
non-standard Gibbs free energy
delta G= delta G°+RTlnQ R= 8.314 J/molK
Equation when non-standard delta G=0
delta G°= -RTlnK
Gibbs free energy
delta G°= delta H-T deltaS Determines the extent that reactants in a given reaction are converted to products The energy available for a system to do work
Consider the following double replacement reaction between silver nitrate and sodium chloride:AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq) Which of the following is the correct expression needed to calculate delta H rxn?
delta H[AgCl(s)] + [NaNO3(aq)]-[AgNO3(aq)] - [NaCl(aq)]
Rate law
k[A][B]^2
The follwing rate data is obtained for two reactoins: X->Y rate= 1.4 Y->X rate= 6.5 What is the equilibrium constant for the reaction?
kf/kr= 1.4/6.5= 0.21
Exergonic
negative delta G spontaneous forward reaction, reverse reaction is endergonic
delta G> 0
non-spontaneous forward reaction Q>K Reactants are favored
A hypothetical compound with t1/2 = 1.4 days decomposes according to second order kinetics and has a concentration of 0.32 M after 0.64 days have elapsed. Find its initial concentration
t1/2= 1.4= 1/k[A]0 k= 1/1.4[A0] 1/[A]t= kt+ 1/[A0] 1/0.32= k(0.64) +1/[A0] 1/0.32= 1/1.4[A0] (0.64)+ 1/[A0] 1/0.32= 1.46/[A0] [A0]= 0.47M
A compound has a half life of 5.2 days and decays following first order kinetics. What percent of the original sample remains after 20 days?
t1/2= 5.2 days= ln2/k k= 0.1333 days^-1 ln[A]= -kt + ln[A]0 ln[A]= (-0.1333(20)) + ln1 A= 0.070 7.0% of the compound remains after 20 days
