Question

2. Formation of a solution from two components can
be considered as
(i) Pure solvent separated solvent molecules, AH,
(ii) Pure solute separated solute molecules, AH,
(ii) Separated solvent and solute molecules →
solution, ΔΗ.
Solution so formed will be ideal if
(1) ΔΗ = ΔΗ, + ΔΗ, + ΔΗ,
(2) ΔΗ. - ΔΗ, + ΔΗ, - ΔΗ,
(3) ΔΗ. - ΔΗ, - ΔΗ, - ΔΗ,
(4) ΔΗ = ΔΗ, - ΔΗ, - ΔΗ,
in molecular mass​

Answer 1

Student-name Arti answered this.Thank her not me.

It can be understood with the help of Hess'Law. It states that the total amount of heat evolved or absorbed in a chemical process is the same whether the process takes place in one or in several steps.Apply the Hess law in your question.

Let the Pure solvent is A2 and pure solute is B2.And then try to write up the steps.

A2 -> 2A (enthalpy change = ΔH1 )................step-1

B2 -> 2B (enthalpy change = ΔH2 )................step-2

2A +2B -->2AB (enthalpy change = ΔH3 )......step-3

Now the above 3 steps can be written in single step:

A2 + B2 →2AB.......................step-4

​Now by adding step-1 and step-2 to step-3 we are cancelling the common term in left and right to get the equation in step-4.

overall enthalpy change ΔH = ΔH1 + ΔH2 + ΔH3

​So third option is correct.