# Thermodynamics, Kinetics and Equilibrium

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27 Οκτ 2013 (πριν από 4 χρόνια και 7 μήνες)

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Thermodynamics, Kinetics and Equilibrium

Word

Definition

Effective collision

A collision between reactant particles that results in a chemical reaction taking
place.

Reaction rate

The amount of reactant consumed or product formed per unit of time.

Cata
lyst

A substance that is added to a reaction to increase the reaction rate by
decreasing the activation energy without being consumed itself.

Heat of reaction

H

heat of the products minus heat of reactants.

Activation energy

The energy that must be a
dded to the reactants to allow them to react.

Activated complex

intermediate stage in a reaction between reactants and products

Entropy

A system’s state of disorder or randomness.

Spontaneous

A change that, once started, continues the rest of the way
on its own.

Nonspontaneous

A change that requires a constant input of energy to occur.

Equilibrium

A condition where the rate of the forward change equals the rate of the reverse
change.

Enthalpy

H

same as heat of reaction

Energy of Chemical Reacti
ons

A. Chemical Kinetics

1.
Chemical Kinetics

relates to movement of reacting particles

2. Explain
the collision theory

of reactions

a.) Chemical change may occur when reactant particles collide.

b.) The relative particle velocity must be large to prod
uce an effective collision.

c.) The particles must collide with proper alignment to product a chemical
change

3. Account for the factors that affect reaction rates: nature of reactants, surface area,
concentration, temperature of reacting system, presence

of a catalyst

a.)Nature of reactants

o

Ionic compounds react faster than covalent/molecular compounds

b.) Surface area

o

Solids only react on their surface

o

Smaller solid particles have more surface area per gram

Powder will react faster than chunks

c.) Concentration

o

Solid and liquid reactants have a constant concentration

o

Solutions and gases have variable concentrations

o

The greater the concentration of mobile particles the greater the
probability of collision

Faster rat
e of reaction

d.) Temperature

o

Temperature equals the average kinetic energy of the system

o

An increase in temperature increases the rate of
ALL
chemical
reactions

o

Higher temperature causes a greater frequency of collisions

o

Higher temperature causes greater
percentage of collisions
occurring with sufficient energy

effective collisions

e.) Catalyst

o

A catalyst lowers the
activation energy

required to start the reaction

o

A catalyst increases the rate of all chemical reactions (both forward
and reverse reactions
)

o

A catalyst is not consumed during a chemical reaction

f) Pressure

o

Pressure only effects gases

o

An increase in pressure reduces the volume of a gas and acts like
an increase in concentration of that gas, which will increase the
effective collisions (and t
herefore reaction rate)

B.

Thermodynamics

1.
Thermodynamics

relates to transfer of energy between kinetic energy and potential

energy.

2. Interpret potential energy diagrams

a.) Potential energy diagrams

o

The symbol “

H” is the change in en
thalpy, or heat

o

H
reaction
= [H
products
]

[H
reactants
]

o

The reaction is labeled an
endothermic reaction

if the energy of
products is greater than reactants

energy is absorbed

o

H is positive for endothermic reactions

o

The reaction is labeled an
exotherm
ic reaction

if the energy of
reactants is greater than products

energy is released

o

H is negative for exothermic reactions

o

A graph may be used to show energy changes during a chemical
reaction.

3. Interpret significance of changes of heat in chemi
cal or physical changes using
Reference Table I

a.) If

H is negative

heat is released = Exothermic (note at bottom of Table I

b.) If

H is positive

heat is absorbed = Endothermic

4. Describe the role o
f changes in entropy on chemical and physical changes

a.)
Entropy

is randomness or disorder

b.) High temperature favors large entropies

c.) Low temperature favors low entropies

d.) Entropy is related to the phase of matter
-
Solids have low entropy

Gases
h
ave high entropy

e.) An increase in total entropy of a system favors a spontaneous change

C. Chemical Equilibrium

1. During
chemical equilibrium
the
rate

of a forward reaction is equal to the
rate

of a
reverse reaction. (The
concentrations

of the products

and reactants
are constant

NOT

equal
)

2. Le Chatelier's Principle states that when a stress is placed on a system that

system will shift in a direction to relieve that stress. The reaction will shift
A
way
from any
A
dded stress, and
T
owards any stre
ss
T
aken or removed.

a)

Stresses

o

Pressure

For solid and liquid systems changes in pressure have no
effect

Pressure affects some systems containing gases

The side with more moles of gas is the one being stressed

If there is an equal amount of moles of gas on b
oth sides
the reaction is not stressed

o

Temperature

o

The side of the reaction containing energy is the one that is
stressed

o

Concentration

o

An increase in the concentration of any reactant causes the
reaction to shift toward the product side and vice versa

o

A d
ecrease in the concentration of species causes the
reaction to shift toward that species

o

Catalyst

o

A catalyst affects both sides of a reaction equally, so it is not a
stress

1) Kinetics Homework

1) Explain how the following will affect the reaction rat
e (increase, decrease, remains the same):

2

(g) to the reaction N
2

+ 3 H
2

2 NH
3

(g)

____
Increase
_________________

b) Removing H
2

(g) from the reaction N
2

+ 3 H
2

2 NH
3

(g)

____
Decrease
_________________

c) Increasing the press
ure on the reaction N
2

(g) + 3 H
2
(g)

2 NH
3

(g)

____
Increase
_________________

d) Using powdered NaCl instead of large crystal NaCl in a reaction

____
Increase
_________________

e) Adding water catalyst to a double replacement reaction

____
Increase
___
______________

f ) Increasing pressure on Na (s) + ZnSO
4

(aq)

Na
2
SO
4

(aq) + Zn (s)

____
Remain the same
__________

2) Place three 5.0 gram samples of sugar in three different 50.0 mL samples of pure water in three different
insulated cups, all at 50.0

o
C. Sample A is a single cube of sugar, Sample B is granulated sugar and Sample C
is powdered sugar. Which sample will dissolve slowest? Explain.

The sugar cube will dissolve the slowest because it has the smallest surface area. A smaller
surface ar
ea decreases the likelihood for effective collisions and therefore decreases rate of
dissolution.

3) Place three identical 5.0 g cubes of sugar into three different 50.0 mL samples of pure water in three
different insulated cups. Cup A contains wa
ter at 20
o
C, Cup B contains water at 10
o
C and Cup C contains
water at 40
o
C. In which cup will the sugar dissolve fastest? Explain.

Cup C will dissolve the fastest because at higher temperatures particles have higher average
kinetic energy. With more
energy, particles move faster and the likelihood of effective collisions is
increased.

2) Potential Energy Diagrams Homework

1) Rewrite the following reactions from Reference Table I, placing the energy on the appropriate side:

Reaction

Rewritten with

Energy on the Correct Side

N
2

(g) + 3 H
2

(g)

2 NH
3

(g)

N
2

(g) + 3 H
2

(g)

2 NH
3

(g) + 91.8kJ

N
2

(g) + 2 O
2

(g)

2 NO
2

(g)

66.4 kJ + N
2

(g) + 2 O
2

(g)

2 NO
2

(g)

H
2

(g) + I
2

(g)

2 HI (g)

53.0 kJ + H
2

(g) + I
2

(g)

2 HI (g)

2) For the
same reactions above, indicate if they are endothermic or exothermic and also indicate whether the
products are stable or unstable.

Reaction

Exothermic or
Endothermic?

N
2

(g) + 3 H
2

(g)

2 NH
3

(g)

Exothermic

N
2

(g) + 2 O
2

(g)

2 NO
2

(g)

Endothermic

H
2

(g) + I
2

(g)

2 HI (g)

Endothermic

3) For the following blank PE Diagram, sketch the shape of an
endothermic

curve and label the H
reactants
,
H
products
, H
activated complex
, activation energy and

H. You do not have to put any numbers in.

4) For the following blank PE Diagram, sketch the shape of an
exothermic

curve and label the H
reactants
, H
products
,
H
activated complex
, activation energy and

H. You do not have to write any numbers in.

5) For the following PE Diagram, answer the ques
tions below:

1) What is the heat of reactants?

a) 20 kJ

b) 50 kJ

c) 90
k
J

d) 30 kJ

2) What is the heat of the products?

a) 20 kJ

b) 50 kJ

c) 90
k
J

d) 30 kJ

3) What is the heat of the activated complex?

a) 20 kJ

b) 50 kJ

c) 90
k
J

d) 30 kJ

4) What is the activation energy for this reaction?

a) 90 kJ

b) 70 kJ

c) 30
k
J

d) 40 kJ

5) What is the

H of this reaction?

a) + 30 kJ

b)

30 kJ

c) +70 kJ

d)
-
70 kJ

6) Draw a dashed line on the above diagram to indicate what the graph would look like if a catalyst was added to this
reaction.

7) What type of reaction is this?

a) exothermic

b) end
othermic

c) both

d) neither

6) For the following PE Diagram, answer the questions below:

1) What is the heat of reactants?

a) 30 kJ

b) 110 kJ

c) 140 KJ

d) 160 kJ

2) What is the heat of the products?

a) 30 kJ

b) 110 kJ

c) 140 KJ

d
) 160 kJ

3) What is the heat of the activated complex for the uncatalyzed reaction?

a) 30 kJ

b) 110 kJ

c) 140 KJ

d) 160 kJ

4) What is the activation energy for the catalyzed reaction?

a) 30 kJ

b) 110 kJ

c) 140 KJ

d) 160 kJ

5) What is th
e

H of this reaction?

a) + 80 kJ

b)

80 kJ

c) +130 kJ

d)
-
130 kJ

6) Draw a dashed line on the above diagram to indicate what the graph would look like if a catalyst was added to this
reaction, using the catalyzed reaction line as your guide.

7)
What type of reaction is this?

a) exothermic

b) endothermic

c) both

d) neither

7) For the following PE Diagram, what does each arrow represent?

a) Heat of Reactants

___
A
_____

b) Heat of Products

___
E
_____

c) Activation

Energy

___
B
_____

d)

H

___
C
__
_
__

e) Heat of Act. Cmplx

___
D
_____

f) Sketch a dashed line to indicate the effect of

3) Will A Reaction Happen On Its Own Once Started? Homework

1) Does entropy increase or decrease in the
following phase changes and reactions? Are these favored or
unfavored changes?

Reaction

Entropy Increase or
Decrease?

CO
2

(s)

CO
2

(g)

Increase

I
2

(g)

I
2

(s)

Decrease

C (s) + O
2

(g)

CO
2

(g)

Decrease

4 Al (s) + 2 O
2

(g)

2 Al
2
O
3

(s)

Decrease

2 CO (g) + O
2

(g)

2 CO
2

(g)

Decrease

2 H
2

(g) + O
2

(g)

2 H
2
O (l)

Decrease

2) Water freezes only at temperatures of 0
o
C and below.

a) Is this an increase or decrease in entropy?___
Decrease
_____________________________

b) When water freezes, is
this exothermic or endothermic?___
E
x
othermic
__________________

3) You have a NiMH AAA rechargeable battery in your mp3 player. After a while, the battery indicator shows
that the battery is losing its charge (running out of “juice”) and needs to be recha
rged, which you do by
placing the battery into a recharger and plugging it into the outlet in your room. After a few hours, the charger
shows that the battery is now full, so you take it out and put it back in your mp3 player and rock to the tunes.

a) Is

discharging the battery endothermic or exothermic? Why?

Exothermic, energy is being released and used by the mp3 player.

b) Is recharging the battery endothermic or exothermic? Why?

Endothermic, energy is being added to the battery.

4
) Equilibrium S
ystems Homework

1) find the heat of reaction for the following and indicate whether they are endothermic or exothermic:

a) 2 H
2

(g) + O
2

(g)

2 H
2
O (g)

________
exothermic
_____________________________

b) N
2

(g) + 3 H
2

(g)

2 NH
3

(g)

________
exother
mic
_____________________________

c) 2 C (s) + H
2

(g)

C
2
H
2

(g)

________
endothermic
____________________________

2) In your opinion, why does the system have to be closed at equilibrium? Please demonstrate thought in

A system must be clo
sed to equilibrate because the conditions in an open system such as temperature, pressure, and
vapor pressure are constantly changing. A closed system will not lose heat or water to the surroundings.

3) What has to be equal at equilibrium?

a)

the mass of

the products and reactants

b)

the volume of the products and reactants

c)

the concentration of the products and reactants

d)

the rates of formation of the products and reactants

4) A stoppered bottle contains 20 grams of liquid water and 20 grams of water vap
or. Does equilibrium exist?

a)

Yes, the amount of each component is equal

b)

Yes, the bottle is stoppered

c)

Only if the rates of evaporation and precipitation are equal

d)

Only if all three of the above are true

5) What word is used to describe a solution at equi
librium?

a) saturated

b) unsaturated

c) supersaturated

d) wet

5) Changing Equilibrium Homework

A) 2 NH
3

(g) + heat

N
2

(g) + 3 H
2

(g)

1) Stress: increase in [N
2
].

Direction of Shift:___
to the left
________________
_____

What is the resulting effect on the concentration of:

a) [NH
3
]____
Increase
____________________

b) [H
2
]_____
Decrease
____________________

2) Stress: increase in temperature

Direction of Shift:____
to the right
___________
_________

What is the resulting effect on the concentration of:

a) [N
2
]_____

Increase
____________________

b) [NH
3
]___

Decrease
______________
_
_____

3) Stress: increase in pressure

Direction of Shift:____
to the
left
__________
__________

What is the resulting effect on the:

a) number of moles of N
2
____
Decrease
__________________

b) number of moles of NH
3
___
Increase
__________________

B) 2 NO (g)

N
2

(g) + O
2

(g) + heat

4) Stress: decrease in [O
2
]

Direction of Shift:_____
to the right
___________________

What is the resulting effect on the concentration of:

a) [N
2
]____
Increase
_____________________

b) [NO]___
Decrease
______________________

5)

Stress: decrease in temperature

Direction of Shift:_____
to the right
___________________

What is the resulting effect on the concentration of:

a) [O
2
]____
In
crease
_____________________

b) [NO]___
_
Decrease
_____________________

6) Stress: increase in pressure

Direction of Shift:____
No effect
____________________

What is the resulting effect on the:

a) number of moles of O
2
____
No change
__________________

b) number of moles of NO____
No change
____________
______

C) Complete the following questions:

Given the equilibrium N
2

(g) + 3 H
2
(g)

2 NH
3
(g)

+ heat :

a) If N
2

is added to the system at equilibrium, which direction will the equilibrium shift?

1. Forward

2. Reverse

b) If H
2

is removed from the system at equilibrium, which direction will the equilibrium shift?

1. Forward

2. Reverse

c) If NH
3

is added to the system at equilibrium, which direction will the equilibrium shift?

1. Forward

2. Reverse

d) If temperature i
s decreased to the system at equilibrium, which direction will the equilibrium shift?

1. Forward

2. Reverse

e) If pressure is increased to the system at equilibrium, which direction will the equilibrium shift?

1. Forward

2. Reverse

f) If H
2

is
removed from the system at equilibrium, what will happen to the concentrations of (circle your choice for
each)

1.

N
2

{increase}

{decrease} {remain the same}

2.

NH
3

{increase}
{decrease}

{remain the same}

g) If NH
3

is removed from the system at equil
ibrium, what will happen to the concentrations of (circle your choice for
each)

1. N
2

{increase}
{decrease}

{remain the same}

2. H
2

{increase}
{decrease}

{remain the same}

D) Given the equilibrium system H
2

(g) + I
2

(g) + 53.0 kJ

2 HI (g), list four

things that can be done to result in
an increase in the concentration of HI (g).

2
2
, Add heat and Remove HI as it is formed.

E) Given the equilibrium system NaOH (s)

+1

(aq) + OH
-
1

(aq) + 44.51 kJ, list four things that ca
n be done
to result in an increase in the concentration of NaOH (s).