Consider the following reaction: c2h4(g) + f2(g) > c2h4f2(g) delta h = -549 kjestimate the carbon-fluorine bond energy given that the c-c bond energy is 347 kj/mol, the c=c bond energy is 614 kj/mol, and the f-f bond energy is 154 kj/mol.

Bond energy of carbon-fluorine bond is 485 kJ/mol

Explanation:

Enthalpy change for a reaction,  is given as:

Where  and represents average bond energy in breaking "i" th bond and forming "j" th bond respectively. and are number of moles of bond break and form respectively.

In this reaction, one mol of C=C, four moles of C-H and one mol of F-F bonds are broken. One mol of C-C bond, four moles of C-H bonds and two moles of C-F bonds are formed

So,

or,

or,

So bond energy of carbon-fluorine bond is 485 kJ/mol

2fe + 3h2so4 -> fe2(so4)3 + 3h2

it is necessary to balance equations in order to get the proper amount of reactants as well as products in order not to make a miscalculation.

you cannot change the subscripts as that would change the substance itself. for instance, diatomic elements such as h2 only have the subscript two when a gas. another example would be so4, if you were to change the subscript, the element would no longer be sulfate.

we change the coefficients instead as that only changes the number of molecules rather than the substance itself.

hope this !