Chemistry 12
Self Test Sec 2.1 – 2.3
Solutions Sec 2.1 – 2.2
1. Given the reaction:
Characteristics of Dynamic Equilibrium
NO2(g) + CO(g)
NO(g) + CO2(g)
a)
If one mole of NO2 and one mole of CO are mixed in a 1.0 litre container, the rate of
the forward reaction will initially be (fast / slow)
_______fast_________________
b)
Immediately after mixing, the rate of the reverse reaction will be
c)
While the forward rate > the reverse rate, the [NO] and the [CO2] will be
__zero___________
(increasing / decreasing) ______increasing__________________________________
d)
After the initial mixing, the rate of the forward reaction will be
The rate of the reverse reaction will we
e)
_____decreasing.
__________________________increasing.
Once equilibrium is established, what can be said about the rates of the forward and
reverse reaction?
______the rates will be equal_________________________
f)
Once equilibrium is established, what is happening to the [NO]?
__stays constant
g)
Once equilibrium is established, what is happening to the [CO2]? ___ stays constant ___
h)
Once equilibrium is established, what is happening to the [NO2]?
i)
Once equilibrium is established, what is happening to the [CO]?
j)
NO2 is a dark brown colour. All of the other gases are colourless. Describe what will
happen to the colour of the gas mixture from when the NO2 and the CO are mixed
until equilibrium is established.
It will be dark at first ( high [NO2]), then the colour will gradually get lighter
until equilibrium is reached. The final color will be a lighter brown
k)
One mole of NO and one mole of CO2 are mixed. If left alone at a constant temperature
__ stays constant __
__ stays constant
_________equilibrium___________________ will be established. Once this
equilibrium is reached, will the colour be different than the equilibrium in
question "j" ?
NO, it will be the same colour, equilibrium can be approached from both sides of the reaction.
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Chemistry 12
2.
Given the reaction: CO(g) + Cl2(g)
Self Test Sec 2.1 – 2.3
COCl2(g)
One mole of CO and one mole of Cl2 are mixed at a certain temperature. On the axes
below, draw graphs which show how the rates of the forward reaction and the reverse
reaction vary with time.
Reaction Rate
Time
3. Give four characteristics of a system at equilibrium.
1.
The rate of the forward reaction = The rate of the reverse reaction
2.
Microscopic processes (the forward and reverse reaction) continue in a balance
which yields no macroscopic changes. (so nothing appears to be happening.)
3.
The system is closed and the temperature is constant and uniform throughout.
4.
The equilibrium can be approached from the left (starting with reactants) or from the
right (starting with products).
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Chemistry 12
Self Test Sec 2.1 – 2.3
Answers to Self Test Sec 2.3
Enthalpy and Entropy
1.
What is meant by enthalpy?
__heat content or chemical potential energy _______
2.
What is meant by entropy?
3.
In an endothermic reaction, the ____reactants_________________________ have
minimum enthalpy.
4.
In an exothermic reaction, the _________products_____________________ have
minimum enthalpy.
5.
Arrange the following in order from least entropy to greatest entropy:
a) liquids b) gases c) aqueous solutions d) solids
_____________________disorder_______________
__solids__ < ___liquids___ < __aqueous solutions___ < __gases_____
6.
There is a natural tendency toward _________minimum_______________enthalpy
and _________maximum_________ entropy.
7.
A process in which entropy increases and enthalpy decreases will
(go to completion/ reach a state of equilibrium/not occur at all)
8.
A process in which entropy increases and enthalpy increases will
(go to completion/ reach a state of equilibrium/not occur at all)
9.
___go to completion__________
___reach a state of equilibrium____
A process in which entropy decreases and enthalpy decreases will
(go to completion/ reach a state of equilibrium/not occur at all) ___reach a state of equilibrium___
10.
A process in which entropy decreases and enthalpy increases will
(go to completion/ reach a state of equilibrium/not occur at all)
11.
A process in which both the enthalpy and entropy trends favour reactants will
(go to completion/ reach a state of equilibrium/not occur at all)
12.
___not occur at all____________
_______not occur at all________
A process in which both the enthalpy and entropy trends favour products will
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Chemistry 12
Self Test Sec 2.1 – 2.3
(go to completion/ reach a state of equilibrium/not occur at all)
13.
________go to completion_____
A process in which the enthalpy and entropy trends oppose each other will
(go to completion/ reach a state of equilibrium/not occur at all)
14.
15.
__reach a state of equilibrium __
In each of the following, state which has the maximum entropy, (reactants or products)
a)
C(s)
CO2(g)
b)
2Al(s) + 6HCl(aq)
c)
2SO3(g)
d)
e)
2(g)
_______________product________
3H2(g) + 2AlCl3(aq)
_________________products____
2SO2(g) + O2(g)
_____________products______________
HCl(g)
H+(aq) + Cl-(aq)
_________________reactant___________
KOH(s)
K+(aq) + OH-(aq)
________________product____________
For each of the following reactions decide which has minimum enthalpy (reactants or products),
which has maximum entropy (reactants or products), and if the reactants are mixed, what will
happen? (go to completion/ reach a state of equilibrium/not occur at all). Assume there is sufficient
activation energy to initiate any spontaneous reaction.
a)
PCl3(g) + Cl2(g) ; H = +92.5 kJ
PCl5(g)
The ______reactant______________ has/have minimum enthalpy.
The __________products_________ has/have maximum entropy.
If PCl5 is put in a flask what should happen?(go to completion/ reach a state of
equilibrium/not occur at all)
__________________reach a state of equilibrium ___________________
b)
2NO(g) + O2(g)
2NO2(g) + energy
The _________products_______ has/have minimum enthalpy.
The _________reactants_________ has/have maximum entropy.
If NO and O2 were put in a flask, what should happen?(go to completion/ reach a
state of equilibrium/not occur at all)
__________________reach a state of equilibrium _________________
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Chemistry 12
c)
Self Test Sec 2.1 – 2.3
Na2CO3(s) + 2HCl(aq)
2NaCl(aq) + CO2(g) + H2O(l) + 27.7 kJ
The ______products_______ has/have minimum enthalpy.
The _________products_____ has/have maximum entropy.
If Na2CO3(s) + 2HCl(aq) were put in a flask, what should happen?(go to
completion/ reach a state of equilibrium/not occur at all)
______go to completion__________________
d)
2Pb(NO3)2(s) + 597 kJ
2PbO(s) + 4NO2(g) + O2(g) ;
The ______reactant______ has/have minimum enthalpy.
The __________products______ has/have maximum entropy.
If Pb(NO3)2 was put in a flask, what should happen?(go to completion/ reach a state of
equilibrium/not occur at all)
_________________________reach a state of equilibrium_______________
16.
Reactions which result in a/an _____decrease__ in enthalpy and a/an
__increase___ in entropy will always be spontaneous.
17.
Reactions which result in a/an ____increase____ in enthalpy and a/an
__decrease___ in entropy will always be non-spontaneous.
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Chemistry 12
Self Test Sec 2.1 – 2.3
Solutions Intro to Sec 2.4 Factors Affecting Equilibrium
1.
When a chemical system is at equilibrium, when the temperature is increased, the
________endothermic reaction speeds up the most.
2.
In the reaction:
A + B
C + 43.3 kJ
a) When the temperature is increased the (forward/reverse)
reaction speeds up more.
________reverse_______
b) During this time, the [A] and [B] will _____crease and the [C] will ______decrease.
c) Because [A] and [B] are _______increasing, the rate of the
reaction will increase.
________forward____
d) Sooner or later, the forward rate and the reverse rate will again become
___equal__.
At this point a new __________equilibrium_________ is established.
e) In the new equilibrium, [A] and [B] will be __________higher than they were
before the temperature is increased.
In the new equilibrium, [C] will be ________________lower than it was before.
f) In this example, we say that the equilibrium has shifted to the
3.
Given the reaction:
A + B
________left______
C + 43.3 kJ
a) When the temperature is decreased the (forward/reverse)
___________forward___
reaction will be the faster one.. (the endothermic reverse reaction slows down)
b) During this time, the [A] and [B] will ____decrease and the [C] will ____increase.
c) Because [C] is _________increasing, the rate of the
reaction will increase.
____________reverse_____
d) Sooner or later, the forward rate and the reverse rate will again become
__equal___.
At this point a new ___________equilibrium______ is established.
e) In the new equilibrium, [A] and [B] will be ____________lower than they were
before the temperature is increased.
In the new equilibrium, [C] will be ________________higher than it was before.
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Chemistry 12
Self Test Sec 2.1 – 2.3
f) In this example, we say that the equilibrium has shifted to the
4.
In the reaction:
A + B + 324 kJ
______right______
C
a) When the temperature is increased the (forward/reverse)
reaction speeds up more.
__________forward______
b) During this time, the [A] and [B] will ____decrease and the [C] will _____increase.
c) Because [C] is _increasing, the rate of the _____________reverse_____
reaction will increase.
d) Sooner or later, the forward rate and the reverse rate will again become
__equal__.
At this point a new __________equilibrium__________ is established.
e) In the new equilibrium, [A] and [B] will be _____________lower than they were
before the temperature is increased.
In the new equilibrium, [C] will be ________________higher than it was before.
f) In this example, we say that the equilibrium has shifted to the
5.
Given the equilibrium:
B(g) + C(g)
________right_____
D(g) + E(g) + heat
a) Some B is added to the mixture at equilibrium. The rate of the
________forward_____
reaction will increase due to the increase in the [B].
b) While this is happening, the [D] and [E] will gradually ______increase.
c) The ____increase in the [D] and [E] will cause the rate of the______reverse_____
reaction to increase.
d) When the rates of the forward and reverse reactions are equal, we have a new
___________________________equilibrium________________________
e) Due to the addition of B, the equilibrium will shift to the
[B] and [C] will ______decrease and [D] and [E] will
6.
Given the equilibrium:
B(g) + C(g)
____________right____
_________________increase
D(g) + E(g) + heat
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Chemistry 12
Self Test Sec 2.1 – 2.3
a) Some D is added to the mixture at equilibrium. The rate of the
________reverse______ reaction will increase due to the increase in the [D].
b) While this is happening, the [B] and [C] will gradually ______increase.
c) The _increase in the [B] and [C] will cause the rate of the ____forward__ reaction
to increase.
d) When the rates of the forward and reverse reactions are equal, we have a new
_________________________equilibrium_______________________
e) Due to the addition of D, the equilibrium will shift to the
_______left_______
[B] and [C] will ____increase and [D] and [E] will
7.
Given the equilibrium:
2A(g) + B(g)
____________decrease.
2C(g)
a) If the total pressure on the system is increased, the
___________forward________
reaction will speed up the most. to compensate for the increased pressure.
b) While this is happening, the [C] will _______increase.
c) This _____increase in [C] will cause the _____reverse_____ reaction to speed up.
d) When the new equilibrium is reached, the [A] and [B] will be
___________lower
than before and the [C] will be ____________higher_________ than before.
e) We say that the increase in total pressure has caused the equilibrium to shift to the
_right (the side with the least moles of gas.)_____________________.
8.
Given the equilibrium:
2A(g) + B(g)
2C(g)
a) If the total pressure on the system is decreased, the
reaction will be the faster one.
_____________reverse_____
b) While this is happening, the [A] and the [B] will ________increase.
c) This _____increase in [A] and the [B] will cause the ______forward____reaction
to speed up.
d) When the new equilibrium is reached, the [A] and [B] will be
_________higher
than before and the [C] will be _______lower_________ than before.
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Chemistry 12
Self Test Sec 2.1 – 2.3
e) We say that the decrease in total pressure has caused the equilibrium to shift to the
_______________left____________.
9.
Given the equilibrium :
NO(g) + CO2(g)
NO2(g) + CO(g)
a) Will an increase in total pressure have an affect on the equilibrium?
_____no_____
b) Explain your answer to question (a)
__the same number of moles on both sides.
It could not compensate for the increased pressure by shifting either way.__
10.
Given the equilibrium:
2A(g) + B(g)
2C(g)
a) If the total volume of the system is decreased, the
_____pressure__________
will increase, and the _____forward_______ reaction will be the faster one.
b) While this is happening, the [C] will _________increase.
c) This ___increase in [C] will cause the ____reverse__ reaction to speed up.
d) When the new equilibrium is reached, the [A] and [B] will be
________lower
than before and the [C] will be _______higher_____ than before.
e) We say that the decrease in total volume has caused the equilibrium to shift to the
____________right_______________.
11.
Given the equilibrium:
2A(g) + B(g)
2C(g) + heat
a) How will this equilibrium be affected if a catalyst is added to the mixture? it won't
b) Explain your answer to "a" in terms of forward and reverse reaction rates
a catalyst speeds up the forward rate and the reverse rate by the same amount,
so the rates are still equal and the equilibrium is not affected.
A catalyst will cause a reaction which is not at equilibrium to reach
equilibrium faster.
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