question_answer

For the gas phase reaction, \[PC{{l}_{5}}_{(g)}PC{{l}_{3}}(g)+C{{l}_{2}}(g)\] which of the following conditions are correct? [AIPMT (S) 2008]

A)  \[\Delta H=0\] and \[\Delta S<0\]

B)  \[\Delta H>0\] and \[\Delta S>0\]

C)  \[\Delta H>0\] and \[\Delta S<0\]

D)  \[\Delta H>0\] and \[\Delta S<0\]

Correct Answer: B

Solution :

Key Idea:

number of moles of product - number of moles of reactants For a spontaneous process AC must be negative.

In this reaction

Thus,  is positive, ie, > 0

If  is positive, then to maintain the value of  negative,  should be positive, ie,