One mole of anhydrous MgCl2 dissolves in water and librates 25 cal/mol of heat. ∆Hhydration of MgCl2 = –30 cal/mol. Heat of dissolution of MgCl2.7H2O(s) is :-

(1) +5 cal/mol
(2) –5 cal/mol
(3) 55 cal/mol
(4) –55 cal/mol

Asked by Atulcaald | 25th May, 2018, 12:24: AM

Expert Answer:

Option (1) is correct.
 
Heat of dissolution is + 5 cal/mol.
 
Solution:
Given colon

Heat space liberated space when space MgCl subscript 2 space dissolve space in space water space equals space 25 space cal divided by mol

Heat space of space ionisation space equals space 25 space cal divided by mol

Heat space of space hydration space equals space minus 30 space cal divided by mol

We space have comma space space

Heat space of space solution space equals space Heat space of space ionisation space plus space Heat space of space hydration space

space space space space space space space space space space space space space space space space space space space space space space space space space equals space 25 plus left parenthesis negative 30 right parenthesis

space space space space space space space space space space space space space space space space space space space space space space space space space space equals space left parenthesis negative 5 right parenthesis space cal divided by mol

As space Heat space of space ionisation space greater than space bold space Heat space of space hydration space

therefore space Heat space of space solution space equals space plus space 5 space cal divided by mol
It space is space endothermic space dissolution.
space

Answered by Varsha | 25th May, 2018, 11:31: AM