UNIT 2 Flashcards
When equal volumes of 0.2 M NH4Cl and 0.2 M CuSO4 are combined,
Select one:
a. a precipitate of both (NH4)2 SO4 and CuCl2 forms.
b. a precipitate of (NH4)2 SO4 forms.
c. a precipitate does not form.
d. a precipitate of CuCl2 forms
C.
Careful with this one. Copper (II) Chloride is soluble…it is Copper (I) Chloride that is low solubility.
Consider the following equilibrium:
N2O4(g) ⇌ 2NO2(g)
A 1.00 L container is initially filled with 0.200 mol N2O4At equilibrium, 0.160 mol NO2are present. What is the equilibrium concentration of N2O4?
Select one:
a. 0. 080 mol/L
b. 0.120 mol/L
c. 0.100 mol/L
d. 0. 040 mol/L
e. 0.160 mol/L
B.
First column:
- 20
- 0.08 - 12
Second column:
0
+0.16
0.16
Consider the following equilibrium:
2HBr(g) ⇌ H2(g)+ Br2(g)
Initially, 0.100 mol HBr is placed into a 2.0 L container. At equilibrium, there are 0.040 mol HBr present. The equilibrium concentration of H2 is …..
Select one:
a. 0. 010 mol/L
b. 0. 030 mol/L
c. 0.100 mol/L
d. 0. 015 mol/L
e. 0. 0050 mol/L
D.
From the following, select the situation where both enthalpy and entropy favour the reaction toward products:
**NEEDS PICTURE!
Select one:
a. C
b. D
c. A
d. B
D. To favour products for both, minimum enthalpy (or enthalpy is DECREASING from reactants to products) and maximum entropy (increasing from reactants to products) must occur.
Consider the following equilibrium:
2NO2(g) ⇌ N2O4(g) keq= 1.15
The equilibrium concentration of NO2is 0.50 mol L.
Calculate the equilibrium concentration of N2O4(g).
Select one:
a. 0.29 mol/L
b. 0 .58mol/L
c. 0.43mol/L
d. 0.22 mol/L
(table , but was a broken link)
Consider the following equilibrium:
2 NO (g) + Cl2 (g) 2 NOCl (g)
At constant temperature and volume, Cl2 is added to the above equilibrium system. As equilibrium reestablishes, the
Select one:
a. [NO] will increase.
b. Keq will decrease.
c. [NOCl] will increase.
d. Keq will increase.
C
Consider the following equilibrium:
2 NO (g) + Cl2 (g) 2 NOCl (g) keq = 12
At equilibrium, [NOCl] = 1. 60 mol / L and [NO] = 0. 80 mol / L. The [Cl2] is
Select one:
a. 0.17 mol /L
b. 0. 27 mol /L
c. 0. 33 mol /L
d. 3. 0 mol /L
C
Consider the following:
2 C (s) + O2 (g) 2 CO (g)
A 1.00 L flask is initially filled with 2.00 mol C and 0.500 mol O2 . At equilibrium, the [O2] is
0.250 mol / L. The keq value is
Select one:
a. 2.00
b. 2.25
c. 1.00
d. 0.444
H2+Br<−−>2HBr
Keq=15.0
Equal moles of H2 and Br2 are added to a 2.00 L flask. When equilibrium is reached, the [HBr] = 0.244 M
What was the initial mass of Br2 added to the flask?
x=0.185
mass of Br2 = 59.1 grams initially
H2+I2<−−>2HI
Keq=49.8
500 mL flask
HI = 1.50 mol
Calculate the change in concentrations at equilibrium with the initial HI mol concentration only.
[H2] = 0.331
[I2] = 0.331
[HI] = 2.34
x=0.331
2NO+Cl2<−−>2NO
Keq=6.25x104
[NO] = 0.020 M
[CL2] = 0.040 M
[NOCl] = 0.90 M
Does this go to equilibrium?
No. K trial < K eq (K trial = 50.625). Too low to reach equilibrium. Moves to the right. More Product and less Reactants, and ratio will continue to increase until 6.25 x 10^4 is reached. Then equilibrium will be reached.
Calculate Molarity from being given moles of a substance.
NO = 0.100 mol
CL2 = 0.200 mol
NOCl = 4.50 mol
in a 5.00 L vessel
- 02 M
- 04 M
- 90 M
2H2+S2<−−>2H2S
(all are gases)
Calculate moles of H2 if Keq = 1.08 x 10^7 in a 5.00 L vessel.
S2 = 5.63 X 10^-6 mol
H2S = 3.625 mol
H2 = ?
H2 = 1.04 mol
2NO+Br2<−−>2NOBr
(all are gases)
Calculate Keq.
[NO] = 0.119 M
[Br2] = 0.0595 M
[NOBr] = 1.50 M
2.67 x 10^3
What is Chatelier’s Principle predicting ?
Predicting the effects of changes (pressure, concentrations, temperature) to a system at equilibrium
In an exothermic equilibrium reaction involving only gases, the value of Keq can be decreased by …
Select one:
a. increasing the temperature.
b. decreasing the temperature.
c. decreasing the pressure.
d. removing some reactant gas.
e. adding some reactant gas.
A
What will cause the value of keq for an exothermic reaction to decrease?
Select one:
a. decreasing the temperature
b. decreasing the surface area
c. increasing the pressure
d. increasing the temperature
D
Consider the following equilibrium:
2SO3(g) ⇌ 2SO2(g) + O2(g)
The volume of the system is decreased at a constant temperature. A new state of equilibrium is established by a shift of the original equilibrium to the …
Select one:
a. left and [SO3] increases.
b. right and [SO3] decreases.
c. right and [SO3] increases.
d. right and [SO3] remains unchanged.
e. left and [SO3] remains unchanged.
A
The value of the equilibrium constant will change when ….
Select one:
a. reactant or product concentrations change. This will cause the equilibrium to shift to re-establish equilibrium , but this will not affect the keq. Only temperature will change the equilibrium constant
b. the volume of gaseous systems change.
c. the temperature changes.
d. only product concentrations change.
e. a catalyst is used.
C. Adding more product to change the concentrations will cause the equilibrium to shift to re-establish equilibrium. But not affect Keq.
A catalyst is added to a system already at equilibrium. How are the forward and reverse reaction rates affected by the addition of the catalyst?
Select one:
a. Forward Rate remains constant; Reverse Rate decreases
b. Forward Rate remains constant; Reverse Rate remains constant;
c. Forward Rate increases; Reverse Rate increases
d. Forward Rate increases; Reverse Rate remains constant
C
An indication that an equilibrium system favours the products is a ….
Select one:
a. one step mechanism.
b. low activation energy.
c. large Keq .
d. high activation energy.
e. positive ΔH.
C
An equilibrium system shifts to the left when the temperature is increased. The forward reaction is …
Select one:
a. endothermic and Δ H is negative.
b. endothermic and ΔH is positive.
c. exothermic and ΔH is positive.
d. endothermic and Δ H is zero
e. exothermic and ΔH is negative.
E
Consider the following equilibrium:
N2(g) + 3H2(g) ⇌ 2NH3(g) + 92 kJ
The forward reaction is
Select one:
a. endothermic and entropy is decreasing.
b. endothermic and entropy is increasing.
c. exothermic and entropy is increasing.
d. endothermic and entropy is constant.
e. exothermic and entropy is decreasing.
E
Consider the following reaction:
N2(g) + 3H2(g) → 2NH3(g) + energy
Which of the following describes the changes in enthalpy and entropy as the reaction proceeds?
Enthalpy Entropy
A. Increases Decreases
B. Increases Increases
C. Decreases Decreases
D. Decreases Increases
E. No Change Decreases
C
Consider the following equilibrium:
C(s)+ 2H2(g) ⇌ CH4(g) + 74 kJ
When a small amount of solid C is added to the system …
Select one:
a. [C] increases.
b. [H2] decreases.
c. the temperature increases.
d. [CH4] increases
e. all concentrations remain constant
E. Adding solids does nothing to the concentrations.
Consider the following equilibrium:
N2 (g) + 3 H2 (g) 2 NH3 (g) + 92 kJ
In which of the following will both changes shift the equilibrium right?
Select one:
a. An increase in volume and an increase in temperature.
b. A decrease in volume and a decrease in temperature.
c. An increase in volume and a decrease in temperature.
d. A decrease in volume and an increase in temperature.
B
Consider the following equilibrium:
SO2Cl2 (g) SO2 (g) + Cl2 (g)
A 1.0 L container is initially filled with 2.0 mol of SO2Cl2. As the reaction proceeds towards equilibrium, the rate of the forward reaction:
Select one:
a. increases and the [SO2] increases.
b. decreases and the [SO2] increases.
c. increases and the [SO2] decreases.
d. decreases and the [SO2] decreases.
B.
Initially it increases but as it approaches equilibrium, it decreases.
Consider the following equilibrium:
2SO3 (g) 2SO2 (g) + O2 (g)
The volume of the system is decreased at a constant temperature. A new state of equilibrium is established by a shift of the original equilibrium to the
Select one:
a. right and [SO3] remains unchanged.
b. right and [SO3] decreases.
c. left and [SO3] remains unchanged.
d. left and [SO3] increases.
D. Shifts to side with fewer gas particles and concentration increases while equilibrium established again.
Consider the following equilibrium:
H2 (g) + CO2 (g) CO (g) + H2O (g) ΔH = + 41 kJ
The temperature of the above equilibrium system is increased while kept at a constant volume. A new state of equilibrium is established in which there is
Select one:
a. an increase in [CO 2] and an increase in keq
b. an increase in [CO] and an increase in Keq
c. an increase in [CO 2] and a decrease in Keq
d. an increase in [CO] and a decrease in Keq
B
Temperature will change the keq. In this case, the reaction is endothermic so an increase in temperature will shift the reaction to the right, increasing the concentration of products, and decreasing the concentration of reactants, and increasing the keq
In an exothermic equilibrium reaction involving only gases, the value of keq can be decreased by
Select one:
a. removing some reactant gas.
b. adding some reactant gas.
c. increasing the temperature.
d. decreasing the temperature.
C.
R ↔ P + energy represents an exothermic reaction
Only changing temperature could change a keq. To decrease keq, the concentration of reactants must increase and the concentration of products must decrease and concentration of reactants must increase…As this is an exothermic reaction, when temperature is increased, it will cause a shift to the right (reactants) to reduce the stress and re-establish equilibrium
The correct answer is: increasing the temperature.
In which of the following does the entropy decrease?
Select one:
a. 4NO (g) + 6H2O(g) → 4NH3(g) + 5O2 (g)
b. 2NaHCO3 (s) → Na2CO3 (s) + CO2 (g) + H2O (g)
c. NaCl (s) → Na+ (aq) + Cl− (aq)
d. CaCO3 (s) + 2 HCl (aq) → CaCl2 (aq) + CO2 (g) + H2O (l)
A. Either gas particles decreasing or reactants going from acqueous to solid
Given initial concentrations of all substances and just one concentration at equilibrium, calculate the Keq.
2SO3<−−>2SO2+O2
2.00 L flask
SO3 = 10 mol
[O2] = 0.588 m
[SO3] = 3.824 M
[S02] = 1.176 M
Keq = 0.0556
C2H6<−−>2C+3H2
H=+83kJH = +83 kJH=+83kJ
Min. enthalpy favours the _____
Max entropy favours the _____
Equilibrium, completion, or no reaction at all?
reactants (endo)
products (1 vs. 5 mol)
equilibrium
PCl5+HEAT<−−>PCl3+Cl2
Min. enthalpy favours the _____
Max entropy favours the _____
Equilibrium, completion, or no reaction at all?
reactants (endo)
product (1 vs 2 mol)
equilibrium
2NH4NO3+1Ba(OH)2∗8H2O<−−>10H2O+2NH3+Ba2++2NO3−
Max entropy favours the _____
PRODUCTS
2POCl3<−−>2PCl3+IO3
H = 572 kJ
Min. enthalpy favours the _____
Max entropy favours the _____
Equilibrium, completion, or no reaction at all?
reactants
products
equilibrium
Either entropy or enthalpy must dominate a reaction (min/max), but:
if min. enthalpy favours the reactants, and max entropy favours the products
what happens?
Equilibrium. ENDOTHERMIC.
Either entropy or enthalpy must dominate a reaction (min/max), but:
if min. enthalpy favours the products and max. entropy favours the reactants
what happens?
equilibrium will occur. EXOTHERMIC.
Either entropy or enthalpy must dominate a reaction (min/max), but:
if min. enthalpy and max. entropy favour the reactants
what happens?
No reaction when reactants mixed
Entropy or Enthalpy?
_____ is a thermodynamic quantity equaling the total heat content
_____ is a thermodynamic quantity equaling the unavailability of thermal energy for conversion into mechanical work
Enthalphy, Entropy
1CO+3H2<−−>1CH4+1H2O
Which side has greater entropy?
LEFT SIDE (MORE MOLECULES)
1PCl5<−−−>1Cl2+1PCl3
Which side has greater entropy?
right side. (more molecules)
Would entropy be highest with solids or gases?
GASES
Thinking of an exothermic graph, does enthalpy in equilibrium favour the reactants or products?
PRODUCTS
Thinking of an endothermic graph, does enthalpy in equilibrium favour the reactants or the products?
reactants. HHH is lowest on the reactant side.
Concerning Enthalpy/Entropy, what are the 2 natural tendencies for chemical reactions to progress to?
to have minimum enthalpy (be exothermic)
and
to have maximum entropy (to become more disordered)
1stLaw of Thermodynamics: ?
Law of Conservation of Energy (energy can’t be created or destroyed)
3rd Law of Thermodynamics: explain Entropy.
thermodynamic quantity in a system of equilibrium representing the unavailability of a system’s thermal energy for conversion into mechanical work, often interpreted as the degree of disorder or randomness in the system.
H2O+CL2O<−−>2HOClH2O + CL2O <–> 2HOClH2O+CL2O<−−>2HOCl
K eq = 9.0 x 10^-2
What will happen to the K value if the molar concentrations are squared? (not doubled, squared)
4 HOCl <–> 2H2O + 2CL2O
square the K value, too. [0.09]^2 and since it’s also switched, the reciprocal is applied.
1 / [0.09]^2 = 1.2 x 10^2
H2O+CL2O<−−>2HOCl
Keq = 9.0 x 10^-2
What will happen to the K value if the formula is switched?
2 HOCl <–> H2O + CL2O
The reciprocal. 1 / 9.0 x 10^-2 = 11.1
H2O+CL2O<−−>2HOCl
K eq = 9.0 x 10^-2
What will happen to the K value if the molar concentrations are doubled?
2H2O+2CL2O<−−−>4HOCl
K eq = 1.8 x 10^-1. It will doubled also.
What is the correct equation for mathematically determining the concentrations of a system at equilibrium?
K=reactants/products
OR
K=products/reactants
K=products/reactants
What are two things that can be done to maximise yield of NOCl in this system at equilibrium?
2NO+1CL2<−−>2NOCl
H=−77.2kJ
Increase pressure by reducing volume
Lower the temperature
If a system is in equilibrium and it’s exothermic, when heat is increased, how does the system shift?
LEFT
3 things that will disturb the equilibrium and shift the reaction..?
pressure, temperature, concentration
What is Le Chatelier’s Principle?
Concerning equilibrium (also called the ‘equilibrium law’):
when a system is at equilibrium, and pressure (increasing or decreasing the volume), concentration, temperature are changed, the system will counteract it and establish a new equilibrium.
The change will partially counteract the applied change.
Equilibrium or Completion:
Strong exothermic reactions tend towards _________
Reactions with slight heat expelled tend towards___________
completion —->, equilibrium <—>
Explain chemical equilibrium.
chemical equilibrium is the state in which both reactants and products are present in concentrations which have no further tendency to change with time, so that there is no observable change in the properties of the system.
Usually, this state results when the forward reaction proceeds at the same rate as the reverse reaction
