Question

one mole of diatomic molecule a₂ reacts with one mole of diatomic molecule b₂ to yield two moles of diatomic molecule ab.

calculate the enthalpy of reaction in kj/mol.
express your answer to three significant figures. do not include units in your answer.

Explanation:

Step1: Calculate energy to break bonds

Energy to break \(A - A\) and \(B - B\) bonds:
$$(123 + 234)\text{ kJ/mol}$$

Step2: Calculate energy released from forming bonds

Energy released from forming \(2\) \(A - B\) bonds:
$$2\times345\text{ kJ/mol}$$

Step3: Calculate enthalpy of reaction

Enthalpy of reaction \(\Delta H=\text{(Energy to break bonds)}-\text{(Energy released from forming bonds)}\)
$$\Delta H=(123 + 234)-2\times345$$
$$\Delta H = 357-690$$
$$\Delta H=- 333$$

Answer:

\(-333\)