1-1H + 3-1 H yield 4-2 He
What is energy in Kj per mole?
To calculate the energy change in kilojoules per mole (ΔE) for a chemical reaction, we can use Hess's Law or the concept of bond enthalpies.
Hess's Law states that the total enthalpy change (ΔH) for a reaction can be calculated by the sum of the enthalpy changes for a series of individual steps. In this case, we need to find the difference in enthalpy between the reactants and products.
The balanced chemical equation for the reaction is:
1-1H + 3-1H → 4-2He
First, we need to determine the enthalpy change for each individual bond broken and formed in the reaction. The bond enthalpy values represent the energy required to break or form a bond.
The bond enthalpy of an H-H bond is +436 kJ/mol (energy required to break it), and the bond enthalpy of an H-He bond is -434 kJ/mol (energy released when it forms).
Considering the reaction:
(1-1H - (1 x H-H)) + (3-1H - (3 x H-H)) → (4-2He)
(1 x -434 kJ/mol) + (3 x -436 kJ/mol) = -434 kJ/mol - 1308 kJ/mol = -1742 kJ/mol
The negative sign indicates that the reaction releases energy. Therefore, the energy change in kilojoules per mole (ΔE) for this reaction is -1742 kJ/mol.