Using some of the bond energies, calculate AH(in kJ) for the following reaction: CH4 (g) + 202(g) → CO2(g) + 2H₂O(g) You will need to draw the Lewis Structure for the reactant and product molecules to determine which bond energy values to use. C=C 614 kJ/mol O-H 467 kJ/mol C-H= 413 kJ/mol C=C= 839 kJ/mol O-O 204 kJ/mol O=O= 498 kJ/mol C=O=799 kJ/mol C-C = 347 kJ/mol
Thermochemistry
Thermochemistry can be considered as a branch of thermodynamics that deals with the connections between warmth, work, and various types of energy, formed because of different synthetic and actual cycles. Thermochemistry describes the energy changes that occur as a result of reactions or chemical changes in a substance.
Exergonic Reaction
The term exergonic is derived from the Greek word in which ‘ergon’ means work and exergonic means ‘work outside’. Exergonic reactions releases work energy. Exergonic reactions are different from exothermic reactions, the one that releases only heat energy during the course of the reaction. So, exothermic reaction is one type of exergonic reaction. Exergonic reaction releases work energy in different forms like heat, light or sound. For example, a glow stick releases light making that an exergonic reaction and not an exothermic reaction since no heat is released. Even endothermic reactions at very high temperature are exergonic.
![### Calculating ΔH for a Chemical Reaction
**Objective:** Using some of the bond energies, calculate ΔH (in kJ) for the following reaction:
\[ \text{CH}_4 \text{ (g)} + 2\text{O}_2 \text{ (g)} \rightarrow \text{CO}_2 \text{ (g)} + 2\text{H}_2\text{O} \text{ (g)} \]
You will need to draw the Lewis Structure for the reactant and product molecules to determine which bond energy values to use.
#### Bond Energies
- C=C = 614 kJ/mol
- O-H = 467 kJ/mol
- C-H = 413 kJ/mol
- C≡C = 839 kJ/mol
- O=O = 204 kJ/mol
- O=O = 498 kJ/mol
- C=O = 799 kJ/mol
- C-C = 347 kJ/mol
#### Steps for Calculation
1. **Draw the Lewis Structures** for each molecule in the reaction to identify the types and numbers of bonds.
2. **Calculate the total bond energy** for bonds broken in the reactants.
3. **Calculate the total bond energy** for bonds formed in the products.
4. **Subtract the bond energies of the products from the bond energies of the reactants** to find the overall ΔH:
\[ \Delta H = \Sigma \text{Bond Energies of Reactants} - \Sigma \text{Bond Energies of Products} \]
#### Example Calculation
**Reactants:**
- **CH4**: 4 C-H bonds
- **2 O2**: 2 O=O bonds
**Products:**
- **CO2**: 2 C=O bonds
- **2 H2O**: 4 O-H bonds
### Bond Energies in the Reaction
- **Reactants:**
- C-H: 4 × 413 = 1652 kJ/mol
- O=O: 2 × 498 = 996 kJ/mol
- Total bond energy for reactants = 1652 + 996 = 2648 kJ/mol
- **Products:**
- C=O: 2 × 799 = 1598 kJ/mol
- O-H: 4](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2F0a6c9e0c-0b6a-4785-ae3f-5e292bd65bb9%2F2a033a71-1b20-4fa6-b30a-7842cc49af81%2F0sw5esf_processed.jpeg&w=3840&q=75)
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