Question

If melting one mole of ice to water requires $6$ kJ of enthalpy, then freezing of water to two mole of ice will require ________ kJ of energy.

• A. $6$
• B. $12$
• C. $-12$
• D. $-6$

Answer 1

The correct option is C $-12$

Melting one mole of ice to water$\to 6kj$

Melting 2 moles of ice to water$\to 12kj$

If the reaction is reversed i.e. freezing of water to two moles of ice, energy required would be multiplied with $(-1)$ , here it would be $-12kj$

It is beacuse enthalpy is a state function.