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The heat of combustion of naphthalene at constant volume at 25 degree celsius was found to be -5133 kj/mole calculate the value of enthalpy change at constant pressure at the same temperature
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The heat of combustion of naphthalene at constant volume at 25 degree ...
Enthalpy of a substance can be determined with the help of the formula mentioned below :
ΔH = ΔU + ΔngRT
where H denotes enthalpy , Δng denotes the changes in the number of gas species involved ibn a reaction , R is the universal gas constant and T is the temperature.
the balanced equation for the combustion of naphthalene is as follows:
C10H8 + 12O2 = 10 CO2 + 4 H2O
Here Δng = ( 10-14 )
Δng = -4
on substituting the above value in the equation of enthalpy , we get
ΔH = ΔU
which means ΔH = 5133Kj/MOL - 4 * RT
ΔH = 5133 - 9.91 KJ/MOL
hence ΔH = 5142 KJ/MOL
This question is part of UPSC exam. View all Class 9 courses
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The heat of combustion of naphthalene at constant volume at 25 degree ...
Understanding Heat of Combustion
The heat of combustion is the energy released when a substance undergoes complete combustion with oxygen. In this case, the value provided is -5133 kJ/mol for naphthalene at constant volume.
Difference Between Constant Volume and Constant Pressure
- The heat of combustion measured at constant volume is known as the internal energy change (ΔU).
- The enthalpy change (ΔH) at constant pressure can be derived from the relationship between internal energy and enthalpy.
Relationship Between ΔH and ΔU
- The relationship is given by the equation:
ΔH = ΔU + ΔnRT
- Where:
- Δn = change in the number of moles of gas during the reaction
- R = universal gas constant (approximately 8.314 J/(mol·K))
- T = absolute temperature in Kelvin
Calculating Δn for Naphthalene
- When naphthalene combusts, it produces carbon dioxide and water.
- Typically, this reaction results in an increase in the number of gas moles during combustion.
Example Calculation
- For naphthalene combustion, let’s assume Δn = 2 (as a rough estimate).
- At 25°C (298 K), the equation simplifies to:
ΔH = -5133 kJ/mol + (2 mol)(8.314 J/(mol·K))(298 K)
- Convert J to kJ for ease: 8.314 J = 0.008314 kJ.
Final Calculation
- ΔH = -5133 kJ/mol + (2 * 0.008314 kJ/mol * 298 K)
- ΔH = -5133 kJ/mol + 4.95 kJ/mol
- Therefore, ΔH ≈ -5128 kJ/mol.
Conclusion
The enthalpy change (ΔH) for the combustion of naphthalene at constant pressure is approximately -5128 kJ/mol, indicating that the process is highly exothermic.
The heat of combustion is the energy released when a substance undergoes complete combustion with oxygen. In this case, the value provided is -5133 kJ/mol for naphthalene at constant volume.
Difference Between Constant Volume and Constant Pressure
- The heat of combustion measured at constant volume is known as the internal energy change (ΔU).
- The enthalpy change (ΔH) at constant pressure can be derived from the relationship between internal energy and enthalpy.
Relationship Between ΔH and ΔU
- The relationship is given by the equation:
ΔH = ΔU + ΔnRT
- Where:
- Δn = change in the number of moles of gas during the reaction
- R = universal gas constant (approximately 8.314 J/(mol·K))
- T = absolute temperature in Kelvin
Calculating Δn for Naphthalene
- When naphthalene combusts, it produces carbon dioxide and water.
- Typically, this reaction results in an increase in the number of gas moles during combustion.
Example Calculation
- For naphthalene combustion, let’s assume Δn = 2 (as a rough estimate).
- At 25°C (298 K), the equation simplifies to:
ΔH = -5133 kJ/mol + (2 mol)(8.314 J/(mol·K))(298 K)
- Convert J to kJ for ease: 8.314 J = 0.008314 kJ.
Final Calculation
- ΔH = -5133 kJ/mol + (2 * 0.008314 kJ/mol * 298 K)
- ΔH = -5133 kJ/mol + 4.95 kJ/mol
- Therefore, ΔH ≈ -5128 kJ/mol.
Conclusion
The enthalpy change (ΔH) for the combustion of naphthalene at constant pressure is approximately -5128 kJ/mol, indicating that the process is highly exothermic.
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The heat of combustion of naphthalene at constant volume at 25 degree celsius was found to be -5133 kj/mole calculate the value of enthalpy change at constant pressure at the same temperature
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The heat of combustion of naphthalene at constant volume at 25 degree celsius was found to be -5133 kj/mole calculate the value of enthalpy change at constant pressure at the same temperature for Class 9 2024 is part of Class 9 preparation. The Question and answers have been prepared according to the Class 9 exam syllabus. Information about The heat of combustion of naphthalene at constant volume at 25 degree celsius was found to be -5133 kj/mole calculate the value of enthalpy change at constant pressure at the same temperature covers all topics & solutions for Class 9 2024 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for The heat of combustion of naphthalene at constant volume at 25 degree celsius was found to be -5133 kj/mole calculate the value of enthalpy change at constant pressure at the same temperature.
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