Using the following bond energies, calculate the molar heat of hydrogenation, ΔHhydrogenation, for the conversion of C2H2 to C2H6
CH (triple bond) CH (g) + 2H2 (g) --> CH3CH3 (g)
Well, first of all, we need to look at the bond energies to determine the energy needed for the reaction. The bond energies are as follows:
C≡C: 835 kJ/mol
C-H: 413 kJ/mol
To calculate the molar heat of hydrogenation (ΔHhydrogenation), we need to sum up the bond energies of the reactants and subtract the bond energies of the products. So, let's do some math, shall we?
In the reactant C₂H₂, we have one C≡C bond and two C-H bonds.
Total bond energy of reactant = (1 x C≡C) + (2 x C-H) = (1 x 835) + (2 x 413) = 1661 + 826 = 2487 kJ/mol
In the product C₂H₆, we have three C-C bonds and eight C-H bonds.
Total bond energy of product = (3 x C-C) + (8 x C-H) = (3 x 348) + (8 x 413) = 1044 + 3304 = 4348 kJ/mol
Now, to find ΔHhydrogenation, we subtract the bond energy of the reactant from the bond energy of the product:
ΔHhydrogenation = Total bond energy of product - Total bond energy of reactant
= 4348 kJ/mol - 2487 kJ/mol
= 1861 kJ/mol
So, the molar heat of hydrogenation (ΔHhydrogenation) for the conversion of C₂H₂ to C₂H₆ is 1861 kJ/mol.
Remember, though, that "bond energies" can be a bit clingy, like when you try to break up with your significant other but they just won't let go.
To calculate the molar heat of hydrogenation, ΔHhydrogenation, we need to find the difference in bond energies between the reactants and the products.
Given bond energies:
C-H bond energy: 413 kJ/mol
C-C triple bond energy: 839 kJ/mol
C-C single bond energy: 348 kJ/mol
H-H bond energy: 436 kJ/mol
Now, let's break down the reactants and products into their individual bonds:
Reactants:
1 C-C triple bond (C≡C): -839 kJ/mol
2 H-H bonds (H-H): -2 * 436 kJ/mol
Products:
4 C-H bonds (C-H): -4 * 413 kJ/mol
6 C-C single bonds (C-C): -6 * 348 kJ/mol
To calculate the molar heat of hydrogenation, ΔHhydrogenation, we can use the equation:
ΔHhydrogenation = Σ (ΔHbonds broken) - Σ (ΔHbonds formed)
ΔHhydrogenation = (-839 kJ/mol) + (-2 * 436 kJ/mol) - (-4 * 413 kJ/mol) - (6 * 348 kJ/mol)
Simplifying the equation, we have:
ΔHhydrogenation = -839 kJ/mol - 872 kJ/mol + 1652 kJ/mol - 2088 kJ/mol
ΔHhydrogenation = -313 kJ/mol
Therefore, the molar heat of hydrogenation, ΔHhydrogenation, for the conversion of C2H2 to C2H6 is -313 kJ/mol.
To calculate the molar heat of hydrogenation (ΔHhydrogenation) for the conversion of C2H2 to C2H6, you need to determine the energy change associated with breaking the bonds in C2H2 and forming the bonds in C2H6.
First, you need to find the bond energies for the bonds involved in the reaction. Bond energy refers to the amount of energy required to break a particular bond in a molecule. Here are the bond energies you will need for this calculation:
- C≡C triple bond: 837 kJ/mol
- H−H single bond: 436 kJ/mol
- C−C single bond: 348 kJ/mol
- C−H single bond: 413 kJ/mol
Next, you will use these bond energies to calculate the molar heat of hydrogenation:
1. Breaking the triple bond in C2H2:
Since there is one triple bond in the reactant (C2H2), you need to break it. The energy required to break the triple bond is 837 kJ/mol multiplied by the number of moles (1 mol in this case).
Energy change = 837 kJ/mol × 1 mol = 837 kJ
2. Forming the single bonds in C2H6:
The product C2H6 has three C−H bonds and one C−C bond. Multiply each bond energy by the number of moles (1 mol in this case) and sum them up.
Energy change = (413 kJ/mol × 4 moles of C−H bonds) + (348 kJ/mol × 1 mole of C−C bond)
Energy change = (1652 kJ) + (348 kJ) = 2000 kJ
Now, to calculate ΔHhydrogenation, you need to subtract the energy used to break the bonds (bond dissociation energy) from the energy released when forming the new bonds (bond formation energy):
ΔHhydrogenation = Energy released - Energy used
ΔHhydrogenation = Energy change of bond formation - Energy change of bond dissociation
ΔHhydrogenation = 2000 kJ - 837 kJ
ΔHhydrogenation = 1163 kJ
Therefore, the molar heat of hydrogenation (ΔHhydrogenation) for the conversion of C2H2 to C2H6 is 1163 kJ.
dHrxn = [BE reactants] = [BE products]
Here is tutorial
http://www.kentchemistry.com/links/Kinetics/BondEnergy.htm
Post your work if you get stuck.