Calculating heat chnge in a reacti using bond energy?:/

[Mozmozil]

Hello,,can anyone help me with this please ,,

CH4 + 2O2 → CO2 + 2H2O

Energy needed to break bonds: 4 (C-H): 435 x 4 = 1740 KJ/Mol 2 (O=O): 497 x 1 = 994 KJ/Mol Total energy in: 1740 + 994 = 2734 KJ/Mol Energy needed to form bonds: 2 (C=O): 803 x 2 = 1606 KJ/Mol 4 (H-O): 464 x 4 = 1856 KJ/Mol Total energy out: 1606 + 1856 = 3462 KJ/Mol ΔH= 2734 – 3462 = -728 KJ/Mol r Therefore reaction is Exothermic

Now my question is ,,why didnt we time 2O2 by 4 like we did with CH4 ? does this mean that we only consider the number on the right hand side only ? if yes,, then why did we time 2H2O by 4 :/

thanks..

 

[Saadiya Ahmed]

because when u act draw the structure of CH4, u see tht 1 carbon atom is bonded to four other hydrogen atoms and tht's why u multiply the bond energy by 4...whereas in 2O2, O shares a double bond with another O atom and is therefore multiplied by 2..
for understanding bond energies u will have to draw the structure of the molecule and only then will u be able to understand it...
i hope i was able to help!! :|

 

[Mozmozil]

because when u act draw the structure of CH4, u see tht 1 carbon atom is bonded to four other hydrogen atoms and tht's why u multiply the bond energy by 4...whereas in 2O2, O shares a double bond with another O atom and is therefore multiplied by 2..
for understanding bond energies u will have to draw the structure of the molecule and only then will u be able to understand it...
i hope i was able to help!! :|

thanksss ^-^

 

[Saadiya Ahmed]

No prob

 

[JOEJOE]

Change in energy = energy of reactants - energy of products!!!!

if its negative its exo
if +ve its endo!!!!!!!!
Energy would be given..

If they say why is it exo
The energy for bond forming is > than energy needed for bond breaking

Why endo

The energy for bond breaking > than energy for bond forming!!!

 

[Mozmozil]

Change in energy = energy of reactants - energy of products!!!!

if its negative its exo
if +ve its endo!!!!!!!!
Energy would be given..

If they say why is it exo
The energy for bond forming is > than energy needed for bond breaking

Why endo

The energy for bond breaking > than energy for bond forming!!!

Thankooo sooi much .

 

[Abu mota]

Hello,,can anyone help me with this please ,,

CH4 + 2O2 → CO2 + 2H2O

Energy needed to break bonds: 4 (C-H): 435 x 4 = 1740 KJ/Mol 2 (O=O): 497 x 1 = 994 KJ/Mol Total energy in: 1740 + 994 = 2734 KJ/Mol Energy needed to form bonds: 2 (C=O): 803 x 2 = 1606 KJ/Mol 4 (H-O): 464 x 4 = 1856 KJ/Mol Total energy out: 1606 + 1856 = 3462 KJ/Mol ΔH= 2734 – 3462 = -728 KJ/Mol r Therefore reaction is Exothermic

Now my question is ,,why didnt we time 2O2 by 4 like we did with CH4 ? does this mean that we only consider the number on the right hand side only ? if yes,, then why did we time 2H2O by 4 :/

thanks..

i think that the easiest way to do this is to draw them as structural formula and count the number of lines (bonds) and multiply the energy in kj/mol which is usually written in the question. then do this for the exothermic part where u just use negative numbers instead of positive numbers and add the negative number with the positve number if the answer is positive then it is endothermic but if negative then it is exothermic.

 

[Mozmozil]

i think that the easiest way to do this is to draw them as structural formula and count the number of lines (bonds) and multiply the energy in kj/mol which is usually written in the question. then do this for the exothermic part where u just use negative numbers instead of positive numbers and add the negative number with the positve number if the answer is positive then it is endothermic but if negative then it is exothermic.

Thankss .