Chemistry question:
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*dH BE reactants) - (n*dH BE products)
BE = bond energy which you have listed.
To get you started C-H is 99 kcal and you have four of them so you must break 4 C-H bonds at 99 each so it costs almost 400 kcal to break those four bonds. Then you put together CO2 and you must break a O-O bond but form two O=C bonds in forming O=C=O. etc.
To calculate the change in energy for the CH4 - O2 system, we can use the enthalpy of formation values for each compound involved in the reaction. The enthalpy of formation is the energy change that occurs when one mole of a compound is formed from its constituent elements, in their standard states, under standard conditions.
The balanced chemical equation provided is: CH4 + 2O2 → CO2 + 2H2O
We need to calculate the change in energy for the reactants (CH4 and O2) and products (CO2 and H2O) separately, and then subtract the energy change of the reactants from that of the products to determine the overall change in energy.
The enthalpy of formation values for the compounds involved are as follows:
- ΔHf (CH4) = -75 kcal/mol
- ΔHf (O2) = 0 kcal/mol
- ΔHf (CO2) = -94 kcal/mol
- ΔHf (H2O) = -68 kcal/mol
Step 1: Calculate the change in energy for the reactants (CH4 and O2):
The change in energy for CH4 would be ΔH(CH4) = ΔHf (CO2) - ΔHf (CH4).
ΔH(CH4) = -94 kcal/mol - (-75 kcal/mol)
ΔH(CH4) = -19 kcal/mol
The change in energy for O2 would be ΔH(O2) = 2 x ΔHf (O2) (since there are two moles of O2 in the reaction).
ΔH(O2) = 2 x 0 kcal/mol
ΔH(O2) = 0 kcal/mol
Step 2: Calculate the change in energy for the products (CO2 and H2O):
The change in energy for CO2 would be ΔH(CO2) = ΔHf (CO2).
ΔH(CO2) = -94 kcal/mol
The change in energy for H2O would be ΔH(H2O) = 2 x ΔHf (H2O) (since there are two moles of H2O in the reaction).
ΔH(H2O) = 2 x (-68 kcal/mol)
ΔH(H2O) = -136 kcal/mol
Step 3: Calculate the overall change in energy:
The overall change in energy (ΔH) for the system would be:
ΔH = (ΔH(products)) - (ΔH(reactants))
ΔH = (ΔH(CO2) + ΔH(H2O)) - (ΔH(CH4) + ΔH(O2))
ΔH = (-94 kcal/mol + (-136 kcal/mol)) - (-19 kcal/mol + 0 kcal/mol)
ΔH = -230 kcal/mol - (-19 kcal/mol)
ΔH = -211 kcal/mol
Therefore, the change in energy for the CH4 - O2 system is -211 kcal/mol.