Given: CH4 + 2O2 ~ CO2 + 2H2O
C - H = 99 kcal O - O = 119 kcal
C = O = 192 kcal O - H = 111 kcal
Calculate the change in energy for the CH4 - O2 system.
dHrxn = (n*BE reactants) - (n*BE products).
BE = bond energy.
For example You have broken 4 C-H bonds so that is 4*99 = ? kcal.
You have broken 2*119 O bonds = ? kcal
you have formed two C-O bonds for CO2
etc.
To calculate the change in energy for the CH4 - O2 system, we can use the concept of bond energies. Bond energy is the amount of energy required to break a bond between two atoms.
We are given the bond energies for C - H, O - O, C = O, and O - H.
The reaction CH4 + 2O2 → CO2 + 2H2O involves breaking the bonds in CH4 and O2 and forming the bonds in CO2 and H2O.
Let's break it down step by step:
1. Breaking the bonds in CH4:
CH4 → C + 4H
Since there are four C-H bonds, the total energy required will be:
4 * (C - H) kcal
2. Breaking the bonds in O2:
O2 → 2O
Since there are two O-O bonds, the total energy required will be:
2 * (O - O) kcal
3. Forming the bonds in CO2:
C + 2O → CO2
Since there is one C = O bond, the energy released will be:
1 * (C = O) kcal
4. Forming the bonds in 2H2O:
4H + O → 2H2O
Since there are four O-H bonds, the energy released will be:
4 * (O - H) kcal
Now, let's calculate the change in energy:
Change in energy = Energy required for breaking bonds - Energy released by forming bonds
Change in energy = [4 * (C - H) + 2 * (O - O)] - [(C = O) + 4 * (O - H)]
Substituting the given bond energies:
Change in energy = [4 * 99 + 2 * 119] - [192 + 4 * 111]
Change in energy = [396 + 238] - [192 + 444]
Change in energy = 634 - 636
Change in energy = -2 kcal
Therefore, the change in energy for the CH4 - O2 system is -2 kcal.