close

Вход

Забыли?

вход по аккаунту

код для вставкиСкачать
General Chemistry, 5th ed.
Whitten, Davis & Peck
Definitions
Left click your mouse to continue.
Created by Tara L. Moore, MGCCC
DIRECTIONS
• This slide show presentation is designed to
function like flash cards.
• To check your answer, and/or to move on to
the next slide, simply left click your mouse.
Created by Tara L. Moore, MGCCC
ACTIVITY (of a component of
an ideal mixture)
A dimensionless quantity whose
magnitude is equal to molar
concentration in an ideal solution,
equal to partial pressure (in
atmospheres) in an ideal gas mixture,
and defined as 1 for pure solids or
liquids
Created by Tara L. Moore, MGCCC
CHEMICAL EQUILIBRIUM
A state of dynamic balance in which
the rates of forward and reverse
reactions are equal; there is no net
change in concentrations of reactants
or products while a system is at
equilibrium
Created by Tara L. Moore, MGCCC
DYNAMIC EQUILIBRIUM
An equilibrium in which processes
occur continuously, with no net
charge
Created by Tara L. Moore, MGCCC
EQUILIBRIUM CONSTANT, K
• A quantity that indicates the extent to which
a reversible reaction occurs
• Its magnitude is equal to the mass action
expression at equilibrium
• K varies with temperature
Created by Tara L. Moore, MGCCC
HETEROGENEOUS
EQUILIBRIA
Equilibria involving species in more
than one phase
Created by Tara L. Moore, MGCCC
HOMOGENEOUS
EQUILIBRIA
Equilibria involving only species in a
single phase; all gases, all liquids, or
all solids
Created by Tara L. Moore, MGCCC
LeCHATELIER’S PRINCIPLE
If a stress (change of conditions) is
applied to a system at equilibrium,
the system shifts in the direction that
reduces the stress
Created by Tara L. Moore, MGCCC
MASS ACTION EXPRESSION
aA + bB  cC + dD
Q (or K at equilibrium) = [C]c[D]d
[A]a[B]b
Created by Tara L. Moore, MGCCC
REACTION QUOTIENT, Q
• The mass action expression under any set of
conditions (not necessarily equilibrium)
• Its magnitude relative to K determines the
direction in which reaction must occur to
establish equilibrium
Created by Tara L. Moore, MGCCC
REVERSIBLE REACTIONS
Reactions that do not go to
completion and occur in both the
forward and reverse directions
Created by Tara L. Moore, MGCCC
VAN’T HOFF EQUATION
The relationship between H0 for a reaction and
its equilibrium constants at two different
temperatures
ln [KT2/KT1] = (H0/R)(1/T1 – 1/T2)
Or
log [KT2/KT1] = (H0/2.303R) (1/T1 – 1/T2)
Created by Tara L. Moore, MGCCC
For any reaction, the value of Kc
(equilibrium constant)
• Varies only with temperature
• Is constant at a given temperature
• Is independent of the initial concentrations
Created by Tara L. Moore, MGCCC
Q<K
Forward reaction predominates until
equilibrium is established
Created by Tara L. Moore, MGCCC
Q=K
System is at equilibrium
Created by Tara L. Moore, MGCCC
Q>K
Reverse reaction predominates until
equilibrium is established
Created by Tara L. Moore, MGCCC
If a change of conditions (stress)
is applied to a system at
equilibrium
• The system responds in the way that best
tends to reduce the stress in reaching a new
state of equilibrium
–
–
–
–
Concentration changes
Pressure changes (volume for gas phase)
Temperature changes
Introduction of catalysts
Created by Tara L. Moore, MGCCC
When a “new equilibrium” is
established
• The rates of the forward and reverse
reactions are equal again
• Kc is again satisfied by the concentrations
of reactants and products
Created by Tara L. Moore, MGCCC
A decrease in volume (increase in
pressure)
Shifts the reaction in the direction
that produces the smaller number of
moles of gas
Created by Tara L. Moore, MGCCC
An increase in volume (decrease
in pressure)
Shifts the reaction in the direction
that produces the larger number of
moles of gas
Created by Tara L. Moore, MGCCC
If there is no change in the
number of moles of gases in a
reaction
A volume (pressure) change does not
affect the position of equilibrium
Created by Tara L. Moore, MGCCC
An increase in temperature
Favors endothermic reactions
Created by Tara L. Moore, MGCCC
A decrease in temperature
Favors exothermic reactions
Created by Tara L. Moore, MGCCC
n = ?
n = (ngas prod) – (ngas react)
Created by Tara L. Moore, MGCCC
Kp = ?
Kp = Kc(RT) n
Created by Tara L. Moore, MGCCC
Kc = ?
Kc = Kp (RT)- n
Created by Tara L. Moore, MGCCC
For pure solids or liquids
The activity is taken as 1, so terms for
pure liquids and pure solids do not
appear in the K expression for
heterogeneous equilibria
Created by Tara L. Moore, MGCCC
G0 = ?
G0 = -RT ln K
Or
G0 = -2.303 RT log K
R = 8.314 J/(mol*K)
Created by Tara L. Moore, MGCCC
For equilibria that involve only
gases
The thermodynamic equilibrium
constant (related to G0) is Kp
For those that involve species in
solution, it is equal to Kc
Created by Tara L. Moore, MGCCC
G0 < 0; K > 1
Products favored over reactants at
equilibrium
Created by Tara L. Moore, MGCCC
G0 = 0; K = 1
At equilibrium when
[C]c[D]d…=[A]a[B]b…. (very rare
Created by Tara L. Moore, MGCCC
G0 > 0; K < 1
Reactants favored over products at
equilibrium
Created by Tara L. Moore, MGCCC
1/--страниц
Пожаловаться на содержимое документа