Question

how do you work out bond enthalpies? what is the equation for it?

Answer 1

bond enthalpies are generally given in tables, so if you need to know the bond enthalpy of methane, you'd just look up the bond enthalpy for the C-H bond, multiply it by 4 (because there are 4 C-H bonds in a molecule of methane) and get the enthalpy of methane.

Answer 2

Thank you, but I mean in a sense where you are given an equation, for example: CH4+Cl -> CH3 + HCL (electrophillic substition) and you are given the bond enthalpies in a table, how do i get the answer? Is there a specific equation?

Answer 3

using the bond enthalpies, you always use the general formula:\[\Delta H _{rxn} = \Sigma (bonds broken) - \Sigma (bonds formed)\] and that should get you the overall DH