What is the enthalpy change and volume change when two
liquids are mixed to form a non-ideal solution which shows
negative deviation from Raoult's Law ?
Answers
Answer: ∆mixH < 0 ( negative)
∆mixV < 0 ( negative)
Explanation:
Explanation:
1) Ideal solutions
An ideal solution may be defined as the solution which obeys Raoult’s law over the entire range of concentration.
a) Such solutions are formed by mixing two components which are identical in molecular size, in structure and have almost identical intermolecular forces.
b)The intermolecular interactions between the components (A – B attractions) are of same magnitude as the intermolecular interactions in pure components (A- A and B-B attractions).
According to Raoult’s law, the partial vapour pressure of two components of the solution may be given as :
pA = pA°xA
pB = pB°xB
Total pressure p is given by
p= pA +pB
p= pA°xA + pB°xB
The ideal solutions have also the following characteristics:
1) Heat change on mixing is zero: Since there is no change in magnitude of the attractive forces in the two components present, the heat change on mixing i.e. ΔmixingH in such solutions must be zero.
2) Volume change on mixing is zero: In ideal solutions, the volume of the solution is the sum of the volumes of the components before mixing i.e. there is no change in volume on mixing or Δmixing V is zero.
The solutions generally tends to become ideal when they are dilute.
The characteristics of an ideal solution may be summed up as follows
(i) It must obey Raoult’s law.
(ii) Δmixing H should be zero.
(ii) Δmixing V should be zero.
Example of Ideal Solutions
(i) Benzene and toluene
(ii) n-hexane and n-heptane
(iii) Bromoethane and iodoethane
(iv) Chlorobenzene and bromobenene
Solutions which obey Raoult’s law are called ideal liquid solution.
Composition in Vapour Phase
The composition of vapour phase in equilibrium with the solution is determined by the partial pressure of the components. If y1and y2 are the mole fraction of the two components 1 and 2 respectively in the vapour phase, then according to Dalton’s law of partial pressures:
Partial pressure of a component =Mole fraction of the component x Total pressure
p1= y1 p
p2 =y2 p
In general, Pi = yi p total
Mole fraction of component 1 in vapour phase y1 = p1/p
Mole fraction of component 2 in vapour phase, y2 = p2 /p
Mole fraction of a component in vapour phase =
Partial vapour pressure of component
—————————————————-
Total Vapour Pressure
2) Non-ideal solutions
The solutions which do not obey Raoult’s law over the entire range of concentration are called non-ideal solutions. Therefore, for such solutions
pA ≠ pA° xA
pB ≠ pB° xB
The vapour pressure of such solutions is either higher or lower than that predicted by Raoult’s law.
In non-ideal solutions, there is a noticeable change in volume and heat energy when the two components are mixed.
Most of the solutions are non-ideal because they deviate from ideal behaviour to more or less extent.
Thus, for non-ideal solutions,
a) none of the components obey Raoult’s law over the entire composition range, i.e.
pA ≠ pA° xA and pB ≠ pB° xB
b) Δmixing H is not equal to zero
(ii) Δmixing V is not equal to zero
Types of Non-ideal Solutions
Non-ideal solutions show positive and negative deviations from the ideal
behaviour depending upon their nature.
(1) Non-ideal solutions showing positive deviations from Raoult’s law
(2 ) Non-ideal solutions showing negative deviations from Raoult’s law.
hope it helps you ♥️♥️
