Using the following thermochemical data, what is the change in enthalpy for the following reaction?

a.

120.9 kj

b.

-251.1 kj

c.

251.1 kj

d.

-120.9 kj

D. -120.9 kJ

Explanation:

According to Hess's law ,the total enthalpy change for a reaction is the sum of all changes regardless of the stages or the steps of the reaction.

....(1)

(this reaction should be reversed in order to reach the required reaction )

On reversing the reaction the sign of get reversed.

(In this case change sign from '-' to'+'. Hence   = + 65 kJ)

....(1)

......(2)

Adding equation (1) and (2)

(It is nearly equal to -120.9 kJ)

the correct answer would be d. hope this !