What Is The Enthalpy Of Combustion When 1 Mol $C_6H_6(g)$ Completely Reacts With Oxygen?Reaction: $2 C_6H_6(g) + 15 O_2(g) \rightarrow 12 CO_2(g) + 6 H_2O(g)$Options:A. $ − 6339 KJ/mol -6339 \, \text{kJ/mol} − 6339 KJ/mol [/tex]B. $-3169
What is the Enthalpy of Combustion when 1 mol C6H6(g) Completely Reacts with Oxygen?
Understanding the Concept of Enthalpy of Combustion
Enthalpy of combustion is a measure of the energy released when a substance undergoes complete combustion. It is an important concept in chemistry, particularly in the field of thermodynamics. In this article, we will explore the enthalpy of combustion of benzene (C6H6) when it reacts with oxygen.
The Reaction Equation
The reaction equation for the combustion of benzene is:
This equation shows that 2 moles of benzene react with 15 moles of oxygen to produce 12 moles of carbon dioxide and 6 moles of water.
Calculating the Enthalpy of Combustion
To calculate the enthalpy of combustion, we need to determine the energy released when 1 mole of benzene reacts with oxygen. We can do this by using the reaction equation and the standard enthalpies of formation of the reactants and products.
The standard enthalpy of formation of a substance is the energy released or absorbed when 1 mole of the substance is formed from its constituent elements in their standard states. We can look up the standard enthalpies of formation of benzene, oxygen, carbon dioxide, and water in a thermodynamic database.
Standard Enthalpies of Formation
| Substance | Standard Enthalpy of Formation (kJ/mol) |
|---|---|
| C6H6(g) | 49.0 |
| O2(g) | 0.0 |
| CO2(g) | -393.5 |
| H2O(g) | -241.8 |
Calculating the Enthalpy of Reaction
We can now calculate the enthalpy of reaction using the standard enthalpies of formation of the reactants and products.
ΔH = Σ(ΔHf(products)) - Σ(ΔHf(reactants))
ΔH = (12 x -393.5) + (6 x -241.8) - (2 x 49.0) - (15 x 0.0)
ΔH = -4722 - 1450.8 - 98
ΔH = -6171.8 kJ/mol
Calculating the Enthalpy of Combustion
However, we are interested in the enthalpy of combustion of 1 mole of benzene, not 2 moles. To calculate the enthalpy of combustion, we need to divide the enthalpy of reaction by 2.
ΔHcomb = ΔH / 2
ΔHcomb = -6171.8 / 2
ΔHcomb = -3085.9 kJ/mol
Comparing with the Options
Now, let's compare our calculated value with the options provided.
A. -6339 kJ/mol B. -3169 kJ/mol C. -3085.9 kJ/mol
Our calculated value is closest to option C, which is -3085.9 kJ/mol.
Conclusion
In conclusion, the enthalpy of combustion of 1 mole of benzene (C6H6) when it completely reacts with oxygen is -3085.9 kJ/mol. This value is calculated using the standard enthalpies of formation of the reactants and products and the reaction equation.
Frequently Asked Questions about Enthalpy of Combustion
Q: What is the difference between enthalpy of combustion and enthalpy of formation?
A: Enthalpy of combustion is the energy released when a substance undergoes complete combustion, while enthalpy of formation is the energy released or absorbed when 1 mole of a substance is formed from its constituent elements in their standard states.
Q: How is the enthalpy of combustion calculated?
A: The enthalpy of combustion is calculated using the standard enthalpies of formation of the reactants and products, and the reaction equation. The formula for calculating the enthalpy of reaction is:
ΔH = Σ(ΔHf(products)) - Σ(ΔHf(reactants))
Q: What is the standard enthalpy of formation of a substance?
A: The standard enthalpy of formation of a substance is the energy released or absorbed when 1 mole of the substance is formed from its constituent elements in their standard states.
Q: How do I determine the standard enthalpy of formation of a substance?
A: You can look up the standard enthalpy of formation of a substance in a thermodynamic database or calculate it using the standard enthalpies of formation of its constituent elements.
Q: What is the unit of enthalpy of combustion?
A: The unit of enthalpy of combustion is typically kilojoules per mole (kJ/mol).
Q: Can the enthalpy of combustion be negative or positive?
A: Yes, the enthalpy of combustion can be either negative or positive, depending on whether the reaction is exothermic or endothermic.
Q: What is the significance of enthalpy of combustion in real-world applications?
A: Enthalpy of combustion is an important concept in various fields, including chemistry, physics, and engineering. It is used to calculate the energy released or absorbed during combustion reactions, which is crucial in designing and optimizing combustion systems, such as engines and furnaces.
Q: Can the enthalpy of combustion be affected by external factors?
A: Yes, the enthalpy of combustion can be affected by external factors, such as temperature, pressure, and the presence of catalysts or inhibitors.
Q: How do I calculate the enthalpy of combustion of a complex molecule?
A: To calculate the enthalpy of combustion of a complex molecule, you need to break down the molecule into its constituent elements and calculate the standard enthalpies of formation of each element. Then, use the reaction equation and the standard enthalpies of formation of the reactants and products to calculate the enthalpy of reaction.
Q: What are some common mistakes to avoid when calculating the enthalpy of combustion?
A: Some common mistakes to avoid when calculating the enthalpy of combustion include:
- Not using the correct standard enthalpies of formation
- Not accounting for the reaction equation
- Not considering external factors that can affect the enthalpy of combustion
- Not using the correct units
Q: Can the enthalpy of combustion be measured experimentally?
A: Yes, the enthalpy of combustion can be measured experimentally using techniques such as bomb calorimetry or differential scanning calorimetry.