Equilibrium 1 Flashcards
what is equilibirum
Chemical equilibrium is the state, in which both reactants and products are present in concentrations which have no further tendency to change with time. Usually, this state results when the forward reaction proceeds at the same rate as the reverse reaction.
The system here is in dynamic equilibrium and
we can infer the following:
(i) Both the opposing processes occur
simultaneously.
(ii) Both the processes occur at the same rate
so that the amount of ice and water
remains constant.
what is equilibrium mixture
The mixture
of reactants and products in the equilibrium state is called
an equilibrium mixture.
3 types of reactions
(i) The reactions that proceed nearly to
completion and only negligible
concentrations of the reactants are left. In
some cases, it may not be even possible to
detect these experimentally.
(ii) The reactions in which only small amounts
of products are formed and most of the
reactants remain unchanged at
equilibrium stage.
(iii) The reactions in which the concentrations
of the reactants and products are
comparable, when the system is in
equilibrium.
what does the extent to whcih reaction proceeds depend upon
The extent of a reaction in equilibrium
varies with the experimental conditions such
as concentrations of reactants, temperature,
etc.
what happens in solid-liquid equilibrium
Ice and water kept in a perfectly insulated
thermos flask (no exchange of heat between
its contents and the surroundings) at 273K and the atmospheric pressure are in
equilibrium state.
the mass of ice and water do not change
with time and the temperature remains
constant. However, the equilibrium is not
static. The intense activity can be noticed at
the boundary between ice and water.
Molecules from the liquid water collide against
ice and adhere to it and some molecules of ice
escape into liquid phase. There is no change
of mass of ice and water, as the rates of transfer
of molecules from ice into water and of reverse
transfer from water into ice are equal at
atmospheric pressure and 273 K
what is freezing point/melting point
For any pure substance at
atmospheric pressure, the temperature at
which the solid and liquid phases are at
equilibrium is called the normal melting point
or normal freezing point of the substance.
explain liquid vapour equilibrium experiment
in a large transparent box, connected to a u tube with mercury.
Place a petridish wiht some anhydrous cacl2, it will absorb all the water vapour present in the air leaving it dry.
then place a china dish wit some water. the water starts evaporating into the air(water in dish decreases), due to wich air pressure increases and reaches a constna value.
The pressure increases because the water molecules are being added to air. The pressure in exerted on the mercury causing it to rise.
however the mercury wont fall out because pressure increases only up to a certain level. At this level there is equilibirum between the formation of water vapour and condensation back to liquid.
what is vapour pressure
At equilibrium the pressure exerted by the
water molecules at a given temperature
remains constant and is called the equilibrium
vapour pressure of water (or just vapour
pressure of water); vapour pressure of water
increases with temperature
pressure exerted by a vapour when the vapour is in equilibrium with the liquid or solid form,
what does rate of evaporation depend upon
the time taken for complete
evaporation depends on (i) the nature of the
liquid, (ii) the amount of the liquid and (iii) the
temperature.
and the
liquid which has a higher vapour pressure is
more volatile and has a lower boiling point.
why cant equilibirum take place in an open system
When the watch glass is open to
the atmosphere, the rate of evaporation
remains constant but the molecules are dispersed into large volume of the room. As a
consequence the rate of condensation from
vapour to liquid state is much less than the
rate of evaporation. These are open systems
and it is not possible to reach equilibrium in
an open system
when is water and water vapour at equilibrium
Water and water vapour are in equilibrium
position at atmospheric pressure (1.013 bar)
and at 100°C in a closed vessel. The boiling
point of water is 100°C at 1.013 bar pressure.
what is boiling point
For any pure liquid at one atmospheric
pressure (1.013 bar), the temperature at
which the liquid and vapours are at
equilibrium is called normal boiling point of
the liquid. Boiling point of the liquid depends
on the atmospheric pressure. It depends on
the altitude of the place; at high altitude the
boiling point decreases.
what is solid-vapour equilibrium
If we place solid iodine
in a closed vessel, after sometime the vessel gets
filled up with violet vapour and the intensity of
colour increases with time. After certain time the
intensity of colour becomes constant and at this
stage equilibrium is attained. Hence solid iodine
sublimes to give iodine vapour and the iodine
vapour condenses to give solid iodine. The
equilibrium can be represented as,
I
2
(solid) ⇌ I2
(vapour)
Other examples showing this kind of
equilibrium are,
Camphor (solid) ⇌ Camphor (vapour)
NH4
Cl (solid) ⇌ NH4
Cl (vapour)
what is the dynamic equilibrium in solid- liquid solution
Sugar (solution)⇌Sugar (solid), and
the rate of dissolution of sugar = rate of
crystallisation of sugar.
Equality of the two rates and dynamic
nature of equilibrium has been confirmed with
the help of radioactive sugar
what is henry’s law
which states that the mass of a gas
dissolved in a given mass of a solvent at
any temperature is proportional to the pressure of the gas above the solvent.
This
amount decreases with increase of
temperature
