Calculate the standard molar enthalpy for the complete combustion of liquid ethanol (C2H5OH) using the standard enthalpies of formation of the reactants and products (see Appendix 4 in the back of the textbook).
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.
![**Combustion Reaction of Ethanol**
The equation represents the combustion of ethanol:
\[ \text{C}_2\text{H}_5\text{OH} (l) + 3\text{O}_2 (g) \rightarrow 2\text{CO}_2 (g) + 3\text{H}_2\text{O} (g) \]
**Reactants:**
- Ethanol (\(\text{C}_2\text{H}_5\text{OH}\)), in its liquid form.
- Oxygen (\(\text{O}_2\)), in gaseous form.
**Products:**
- Carbon dioxide (\(\text{CO}_2\)), in gaseous form.
- Water (\(\text{H}_2\text{O}\)), in gaseous form.
**Description:**
- This balanced chemical equation describes the complete combustion of ethanol, a type of alcohol, with oxygen.
- The process results in the formation of carbon dioxide and water vapor.
- The coefficients in the equation ensure that the number of each type of atom is the same on both sides, maintaining the principle of conservation of mass.](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2Fbc3eda98-838a-48fa-9790-2f190fa845b2%2Ff2763c59-91f0-4dff-9971-a1fd6aac608c%2Fpcisl5c_processed.png&w=3840&q=75)
![**Calculation of Standard Molar Enthalpy for Ethanol Combustion**
To calculate the standard molar enthalpy for the complete combustion of liquid ethanol (\( \text{C}_2\text{H}_5\text{OH} \)), you will need to use the standard enthalpies of formation for both the reactants and products. This information can be typically found in Appendix 4 at the back of your textbook.
**Step-by-Step Instructions:**
1. **Write the Balanced Chemical Equation:**
The balanced equation for the combustion of ethanol is:
\[
\text{C}_2\text{H}_5\text{OH}_{(l)} + 3\text{O}_2_{(g)} \rightarrow 2\text{CO}_2_{(g)} + 3\text{H}_2\text{O}_{(g)}
\]
2. **Identify the Standard Enthalpies of Formation:**
Refer to Appendix 4 for the standard enthalpies of formation (\( \Delta H_f^\circ \)) of the following:
- Ethanol (\( \text{C}_2\text{H}_5\text{OH} \))
- Oxygen (\( \text{O}_2 \)), typically zero as it is in its elemental state
- Carbon dioxide (\( \text{CO}_2 \))
- Water (\( \text{H}_2\text{O} \))
3. **Apply Hess’s Law:**
Use Hess's Law to find the total enthalpy change of the reaction:
\[
\Delta H_{rxn}^\circ = \sum (\Delta H_f^\circ \text{ of products}) - \sum (\Delta H_f^\circ \text{ of reactants})
\]
4. **Calculate the Standard Molar Enthalpy:**
Plug in the values from Appendix 4 to compute the enthalpy change.
**Understanding the Result:**
The result represents the energy change when one mole of ethanol undergoes complete combustion under standard conditions. This value is crucial in studying the energy efficiency of fuels.
Remember, for precise values and further instruction, refer to the relevant appendix in your textbook.](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2Fbc3eda98-838a-48fa-9790-2f190fa845b2%2Ff2763c59-91f0-4dff-9971-a1fd6aac608c%2Flvtjj3h_processed.png&w=3840&q=75)

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