Use bond energy values to estimate delta H fro the following reaction in the gas phase:
C2H4 + Br2 -> CH2BrCH2Br
I am in dire need of help! Thank you
To estimate ΔH for the reaction using bond energy values, we need to follow these steps:
1. Write the balanced chemical equation for the reaction:
C2H4 + Br2 → CH2BrCH2Br
2. Determine the bonds broken and formed in the reaction:
Bonds broken:
- C-C bond in C2H4 (ethene)
- Br-Br bond in Br2
Bonds formed:
- C-Br bond in CH2BrCH2Br
3. Look up the bond energies for the bonds involved. Here are some typical values (in kilojoules per mole):
C-C bond energy: ~347 kJ/mol
Br-Br bond energy: ~193 kJ/mol
C-Br bond energy: ~276 kJ/mol
4. Calculate the energy change by summing the bond energies of the bonds broken and subtracting the sum of the bond energies of the bonds formed.
ΔH = (bonds broken) - (bonds formed)
= [2 × (C-C bond energy)] + [1 × (Br-Br bond energy)] - [4 × (C-Br bond energy)]
ΔH = [2 × 347 kJ/mol] + [1 × 193 kJ/mol] - [4 × 276 kJ/mol]
ΔH = 694 kJ/mol + 193 kJ/mol - 1104 kJ/mol
ΔH = -217 kJ/mol
Therefore, the estimated ΔH for the reaction C2H4 + Br2 → CH2BrCH2Br is approximately -217 kJ/mol in the gas phase.
Note: These bond energy values are approximate, and actual values may vary slightly.
Of course, I'm here to help! To estimate ΔH for the given reaction using bond energy values, we need to follow these steps:
Step 1: Write the balanced equation for the reaction:
C2H4 + Br2 -> CH2BrCH2Br
Step 2: Calculate the total bond energy of the reactants:
For C2H4:
- C-C bond energy: 2 * C-C bond energy
- C-H bond energy: 4 * C-H bond energy
For Br2:
- Br-Br bond energy: 1 * Br-Br bond energy
Step 3: Calculate the total bond energy of the product:
For CH2BrCH2Br:
- C-Br bond energy: 4 * C-Br bond energy
- C-C bond energy: 1 * C-C bond energy
Step 4: Calculate the ΔH value:
ΔH = (Total bond energy of products) - (Total bond energy of reactants)
Now, we need the bond energy values for each bond involved in the reaction.
Typically, bond energy values can be found in reference tables or databases. One commonly used source for bond energy values is the CRC Handbook of Chemistry and Physics. Let's assume the following approximate bond energy values in kilojoules per mole (kJ/mol):
C-H: 413 kJ/mol
C-C: 346 kJ/mol
C-Br: 288 kJ/mol
Br-Br: 193 kJ/mol
Using these values, we can proceed to calculate ΔH:
Reactants:
C2H4:
- C-C bond energy: 2 * 346 = 692 kJ/mol
- C-H bond energy: 4 * 413 = 1652 kJ/mol
Br2:
- Br-Br bond energy: 1 * 193 = 193 kJ/mol
Total bond energy of reactants = 692 kJ/mol + 1652 kJ/mol + 193 kJ/mol = 2537 kJ/mol
Product:
CH2BrCH2Br:
- C-Br bond energy: 4 * 288 = 1152 kJ/mol
- C-C bond energy: 1 * 346 = 346 kJ/mol
Total bond energy of product = 1152 kJ/mol + 346 kJ/mol = 1498 kJ/mol
ΔH = (Total bond energy of products) - (Total bond energy of reactants)
ΔH = 1498 kJ/mol - 2537 kJ/mol
Therefore, the estimated ΔH for the given reaction in the gas phase is approximately -1039 kJ/mol. Please note that the sign (positive or negative) indicates if the reaction is endothermic (positive) or exothermic (negative). In this case, the reaction is exothermic as it releases energy.
Look up the bond energies for each bond.
Then bond energies broken - bond energies formed = dH rxn
Here is a tutorial + bond energies listed.
http://www.kentchemistry.com/links/Kinetics/BondEnergy.htm