PPT - Chemical Equilibrium | Additional Documents & Tests for Civil Engineering (CE) PDF Download

 Page 1


16 Chemical Equilibrium
1
Chemical Equilibrium
Reactions seldom go complete such that one of the reactants is
exhausted as we have discussed in stoichiometry and limiting
reagent. Instead, they are mostly reversible. For example,
CO (g) + 3 H
2
(g) « CH
4
(g) + H
2
O (g)
The two-head arrow (or equal signs =) indicates that the reaction
goes both ways. Similarly,
N
2
O
4
(colorless gas) « 2 NO
2
(brown gas) (show a film)
When the forward and reverse reaction rates are equal, the system is
said to be at equilibrium.
Page 2


16 Chemical Equilibrium
1
Chemical Equilibrium
Reactions seldom go complete such that one of the reactants is
exhausted as we have discussed in stoichiometry and limiting
reagent. Instead, they are mostly reversible. For example,
CO (g) + 3 H
2
(g) « CH
4
(g) + H
2
O (g)
The two-head arrow (or equal signs =) indicates that the reaction
goes both ways. Similarly,
N
2
O
4
(colorless gas) « 2 NO
2
(brown gas) (show a film)
When the forward and reverse reaction rates are equal, the system is
said to be at equilibrium.
16 Chemical Equilibrium
2
The NASA Computer program CEA (Chemical Equilibrium with
Applications) calculates chemical equilibrium compositions and
properties of complex mixtures. Applications include assigned
thermodynamic states, theoretical rocket performance, Chapman-
Jouguet detonations, and shock-tube parameters for incident and
reflected shocks.
Page 3


16 Chemical Equilibrium
1
Chemical Equilibrium
Reactions seldom go complete such that one of the reactants is
exhausted as we have discussed in stoichiometry and limiting
reagent. Instead, they are mostly reversible. For example,
CO (g) + 3 H
2
(g) « CH
4
(g) + H
2
O (g)
The two-head arrow (or equal signs =) indicates that the reaction
goes both ways. Similarly,
N
2
O
4
(colorless gas) « 2 NO
2
(brown gas) (show a film)
When the forward and reverse reaction rates are equal, the system is
said to be at equilibrium.
16 Chemical Equilibrium
2
The NASA Computer program CEA (Chemical Equilibrium with
Applications) calculates chemical equilibrium compositions and
properties of complex mixtures. Applications include assigned
thermodynamic states, theoretical rocket performance, Chapman-
Jouguet detonations, and shock-tube parameters for incident and
reflected shocks.
16 Chemical Equilibrium
3
1 mol CH
4
2 mol S
2
T = 1000 K
P = 1.5 atm
Countours
show G/RT
Equilibrium
occur at
minimum
G/RT
Page 4


16 Chemical Equilibrium
1
Chemical Equilibrium
Reactions seldom go complete such that one of the reactants is
exhausted as we have discussed in stoichiometry and limiting
reagent. Instead, they are mostly reversible. For example,
CO (g) + 3 H
2
(g) « CH
4
(g) + H
2
O (g)
The two-head arrow (or equal signs =) indicates that the reaction
goes both ways. Similarly,
N
2
O
4
(colorless gas) « 2 NO
2
(brown gas) (show a film)
When the forward and reverse reaction rates are equal, the system is
said to be at equilibrium.
16 Chemical Equilibrium
2
The NASA Computer program CEA (Chemical Equilibrium with
Applications) calculates chemical equilibrium compositions and
properties of complex mixtures. Applications include assigned
thermodynamic states, theoretical rocket performance, Chapman-
Jouguet detonations, and shock-tube parameters for incident and
reflected shocks.
16 Chemical Equilibrium
3
1 mol CH
4
2 mol S
2
T = 1000 K
P = 1.5 atm
Countours
show G/RT
Equilibrium
occur at
minimum
G/RT
16 Chemical Equilibrium
4
A System
Scientific experiments usually
investigate a system, which is
isolated from its environment or
surrounding.
The system can be a nucleus, an
atom, a molecule, a plant, an
animal, an experimental setup, the
Earth, the solar system, the galaxy, or
the universe.
Matter and energy can be transferred
into or out of a system.
The environment or
The surrounding
The open
or
closed
system
Page 5


16 Chemical Equilibrium
1
Chemical Equilibrium
Reactions seldom go complete such that one of the reactants is
exhausted as we have discussed in stoichiometry and limiting
reagent. Instead, they are mostly reversible. For example,
CO (g) + 3 H
2
(g) « CH
4
(g) + H
2
O (g)
The two-head arrow (or equal signs =) indicates that the reaction
goes both ways. Similarly,
N
2
O
4
(colorless gas) « 2 NO
2
(brown gas) (show a film)
When the forward and reverse reaction rates are equal, the system is
said to be at equilibrium.
16 Chemical Equilibrium
2
The NASA Computer program CEA (Chemical Equilibrium with
Applications) calculates chemical equilibrium compositions and
properties of complex mixtures. Applications include assigned
thermodynamic states, theoretical rocket performance, Chapman-
Jouguet detonations, and shock-tube parameters for incident and
reflected shocks.
16 Chemical Equilibrium
3
1 mol CH
4
2 mol S
2
T = 1000 K
P = 1.5 atm
Countours
show G/RT
Equilibrium
occur at
minimum
G/RT
16 Chemical Equilibrium
4
A System
Scientific experiments usually
investigate a system, which is
isolated from its environment or
surrounding.
The system can be a nucleus, an
atom, a molecule, a plant, an
animal, an experimental setup, the
Earth, the solar system, the galaxy, or
the universe.
Matter and energy can be transferred
into or out of a system.
The environment or
The surrounding
The open
or
closed
system
16 Chemical Equilibrium
5
Chemical Equilibrium – a dynamic process
Chemical equilibrium is a state of a system when reaction rates in both
directions are equal. Changes continue at the molecular level, but the
macroscopic properties stay the same. Equilibrium is a dynamic rather than
static process.
Heat is energy flowing from a high temperature object to a low temperature
object. Equilibrium is reached when the temperatures are the same.
Molecules still exchange kinetic energies during collision.
Water flows from a high potential-energy place to a low potential-energy
place. When potential energies are the same, water stops flowing. Water-
molecule diffusion continues.