Equilibrium 2 Flashcards
explain chemical equilibrium
When the rates of the
forward and reverse reactions become equal,
the concentrations of the reactants and the
products remain constant. This is the stage of
chemical equilibrium. This equilibrium is
dynamic in nature as it consists of a forward
reaction in which the reactants give product(s)
and reverse reaction in which product(s) gives
the original reactants.
the equilibrium can be attained in different ways?
If we start with equal
initial concentration of H2
and I2
, the reaction
proceeds in the forward direction and the
concentration of H2
and I2
decreases while that
of HI increases, until all of these become
constant at equilibrium (Fig. 7.5). We can also
start with HI alone and make the reaction to
proceed in the reverse direction; the
concentration of HI will decrease and
concentration of H2
and I2
will increase until
they all become constant when equilibrium is
reached (Fig.7.5). If total number of H and I
atoms are same in a given volume, the same
equilibrium mixture is obtained whether we
start it from pure reactants or pure product.
what are the charcateristics of chemical equilibrium
(i) The concentrations of the reactants and products become constant at equilibrium.
(ii) at chemical equilibrium, the rates of forward and backward reactions become equal and the equilibrium is dynamic in nature.
(iii) The equilibrium can be attaine donly if the products are not allowed to escape.
(iv) the equilibrium can be attained from any direction(whether we start from reactants or products)
(v) Catalysts do not change the state of equilibrium. They help to attin equilibrium faster( they increaee reate of of both forward and backward reacns)
what is the law of constant mass action
The rate at which a substance reacts is directly proportional to it active mass, and hence The rate of chemical reaction is directly proportional to the product of active mass of the reactants.
what is the law of equilibrium
At constant temperature, the products of the molar concentration of the products raised to their respective stoichiometric coefficients in the balanced chemical equation divided by the products of the molar concentrations of the reactants raised to their respective stoichiometric coefficients is a constant.
This constant Kc is called as equilibrium constant( c represents that K is in terms of concentreation)
This statement is called law of chemical equilibriu,
what are homogenous equilibria
In a homogeneous system, all the reactants
and products are in the same phase. For
example, in the gaseous reaction,
N2
(g) + 3H2
(g) ⇌ 2NH3
(g), reactants and
products are in the homogeneous phase.
what is heterogenus equilibria
Equilibrium in a system having more than one
phase is called heterogeneous equilibrium.
Heterogeneous equilibria often involve pure
solids or liquids. We can simplify equilibrium
expressions for the heterogeneous equilibria
involving a pure liquid or a pure solid, as the
molar concentration of a pure solid or liquid
is constant (i.e., independent of the amount
present).
however the molar conc of gases and aqueos solutions keep chaningg
charcatertistics of equilibrium constant
-equilibrium constant K is a constant at a given temperature and does not depend upon the concentration so freactants or products.
-If a reaction is reversed, eq constant is reversed(1/K)
-if a reaction is multiplied by any number n, the eq constant is K raised to n
-If the equation has equilibrium constant K, and the reaction can take place in 2 steps with equilibrium constant K=K1 and K2
then K= K1 x K2
-The numerical value of constant K is not affected by the presence of a catalyst(b//c it speeds up both forward and backward reacn)
what are the 3 main application s of eq constant
predict the extent of a reaction on the basis
of its magnitude,
* predict the direction of the reaction, and
* calculate equilibrium concentrations
what is the relationship of Kc on products and reactant concentration? how is it useful to us?
The numerical value of the equilibrium
constant for a reaction indicates the extent of
the reaction. But it is important to note that
an equilibrium constant does not give any
information about the rate at which the
equilibrium is reached. The magnitude of Kc
or Kp is directly proportional to the
concentrations of products (as these appear
in the numerator of equilibrium constant
expression) and inversely proportional to the
concentrations of the reactants (these appear
in the denominator).
how can magnitude of Kc be used to predict extent of reactions
- If Kc> 10³
, products predominate over
reactants, i.e., if Kc
is very large, the reaction
proceeds nearly to completion. - If Kc
< 10⁻³, reactants predominate over
products, i.e., if Kc
is very small, the reaction
proceeds rarely. - If Kc is in the range of 10⁻³ to 10³ ,appreciable concentrations of both
reactants and products are present.
what is reaction quotient Q
The reaction quotient ( Q
) measures the relative amounts of products and reactants present during a reaction at a particular point in time.
The equilibrium constant helps in predicting
the direction in which a given reaction will
proceed at any stage. For this purpose, we
calculate the reaction quotient Q. The
reaction quotient, Q.
How does Qc help us find out reaction quotient
If Qc > Kc, the reaction will proceed in the
direction of reactants (reverse reaction).
If Qc< Kc , the reaction will proceed in the
direction of the products (forward reaction).
If Qc
= Kc
, the reaction mixture is already
at equilibrium.
