Question

Type the correct answer in the box. Express the answer to two significant figures.

Given:
N2 + 3H2 → 2NH3

Bond Bond Energy (kJ/mol)
N≡N 942
H–H 432
N–H 386

Use the bond energies to calculate the change in enthalpy for the reaction.

The enthalpy change for the reaction is
kilojoules.

Answer 1

Answer: -78

Explanation: I got this correct on Edmentum.

Answer 2

The enthalpy change for the reaction is -78 kJ

Step-by-step explanation:

In the given reaction, 1 mol of
`N\equiv N` and 3 moles of H-H bonds are broken. Also 6 moles of N-H bonds are formed as 1 mol of
`NH_(3)` contains 3 moles of N-H bonds.

Now, energy is released during bond formation. So, for this case, sign of bond energy will be negative. Also energy if supplied during bond breaking. So, for this case, sign of bond energy will be positive.

Hence change in enthalpy of reaction=
`(1* bond enrgy of N\equiv N)+(3* bond energy of H-H)-(6* bond energy of N-H)`=
`(1* 942)+(3* 432)-(6* 386)kJ= -78 kJ`