The enthalpy of the reaction is maximum in which of the following reaction ?
1) NaOH +HBr ------>NaBr+h2o
2)NaOH+HF--------->NaF +h2O

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Solution

1. All the three reactions here are an example of neutralisation reactions between an acid and a a common base NaOH.
2. As we know,heat of neutralisation for strong acid and strong base is between -56 to -57 kJ/mole. This is because ions of strong acid and base are completely dissociated and reaction mainly involves formation of water by H+ and OH-.

H+ + OH−→H2O

and the energy released from the above reaction is almost near to -56 to -57 kJ/mole.

3. But in the case of weak acid strong base neutralisation,energy released is more negative i.e.,the energy released is less. This is because,energy so released by neutralisation of dissociated H+ and OH- is consumed in dissociating the weak acid.

4. Thus out of above three,HF is the weak acid and HBr is strongest acid since Br- so released is stable as negative charge is stabilised over empty d-orbitals.

Thus correct option is 1)formation of NaBr

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