"Given that the bond enthalpy of the carbon-oxygen bonds in carbon monoxide and carbon dioxide are 1073 kJ/mol and 743 kJ/mol respectively, and that of the bond in the oxygen molecule is 496 kJ/mol, calculate the enthalpy change for the combustion of 1 mole of carbon monoxide."
So I have:
2CO2(g) + O2 (g) -> 2CO2(g)
Delta H = (2 mol)(1073 kJ/mol) + (1 mol)(496 kJ/mol)-[(4 mol)(743 kJ/mol)]
Delta H = -330 kJ/mol
But I know that that is not right. It's part of the correct process...what am I missing?
Really? I'm pretty sure part of the process lead to the value -330 kJ/mol...
We're looking for 1 mole of carbon monoxide...is the value we've calculated for 2 moles?
Hm...if I use (2 mol)(743 kJ/mol), I end up with a positive delta H, which doesn't make sense (combustion -> exothermic).
yeah that's right now all you need to do is divide it by 2 because the question says enthalpy change for the combustion of 1 mole of carbon monoxide.
The balanced combustion process for carbon monoxide is as follows,
2CO + O2 --> 2CO2
delta H = delta H (products) - delta H (reactants)
= 2(743) - [2(1073) + 1(496)]
= -1156 kJ/mol of reaction of CO
for 1mol of CO = -1156/2 = -578 kJ/mol
From your given equation for the combustion of carbon monoxide, 2CO(g) + O2(g) -> 2CO2(g), it seems like you have mistakenly written 2CO2(g) on both sides of the equation. The corrected chemical equation for the combustion of 1 mole of carbon monoxide is:
2CO(g) + O2(g) -> 2CO2(g)
Now, let's calculate the enthalpy change for this reaction. The enthalpy change for a reaction can be calculated by summing up the bond energies of the reactants and subtracting the sum of the bond energies of the products.
Given bond enthalpies:
Bond enthalpy (C-O) in CO = 1073 kJ/mol
Bond enthalpy (O=O) in O2 = 496 kJ/mol
Bond enthalpy (C=O) in CO2 = 743 kJ/mol
In the reactants:
2 CO(g): 2 mol x (C-O bond enthalpy) = 2 mol x 1073 kJ/mol = 2146 kJ/mol
1/2 O2(g): 1/2 mol x (O=O bond enthalpy) = 1/2 mol x 496 kJ/mol = 248 kJ/mol
In the products:
2 CO2(g): 2 mol x (2 x C=O bond enthalpy) = 2 mol x (2 x 743 kJ/mol) = 2972 kJ/mol
Enthalpy change (ΔH) = sum of reactants - sum of products
ΔH = [(2 x CO bond enthalpy) + (1/2 x O2 bond enthalpy)] - [2 x (2 x CO2 bond enthalpy)]
ΔH = (2146 kJ/mol + 248 kJ/mol) - (2972 kJ/mol)
ΔH = -578 kJ/mol
Therefore, the enthalpy change for the combustion of 1 mole of carbon monoxide is -578 kJ/mol.