Calculate The Enthalpy Change for The Following Decomposition of Nitroglycerine
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This calculator helps determine the enthalpy change for the decomposition of nitroglycerine (C₃H₅N₃O₉) into its products. The calculation uses standard enthalpies of formation to determine the energy change in the reaction.
Introduction
Nitroglycerine (C₃H₅N₃O₹) is a highly unstable explosive compound that decomposes exothermically. The decomposition reaction releases energy in the form of heat, which is measured as the enthalpy change (ΔH).
The standard decomposition reaction is:
C₃H₅N₃O₉(l) → 3CO₂(g) + 3H₂O(g) + 2N₂(g) + ½O₂(g)
This reaction is highly exothermic, meaning it releases a large amount of heat energy. The enthalpy change for this reaction is typically measured in kilojoules per mole (kJ/mol).
Formula
The enthalpy change for the decomposition of nitroglycerine can be calculated using the standard enthalpies of formation of the reactants and products. The formula is:
ΔH = ΣΔHf(products) - ΣΔHf(reactants)
Where:
- ΔHf(products) = Sum of standard enthalpies of formation of all products
- ΔHf(reactants) = Sum of standard enthalpies of formation of all reactants
For the decomposition of nitroglycerine, the standard enthalpies of formation are typically available in thermodynamic databases.
Example Calculation
Let's calculate the enthalpy change for the decomposition of 1 mole of nitroglycerine using standard enthalpies of formation:
| Compound | State | ΔHf (kJ/mol) |
|---|---|---|
| Nitroglycerine (C₃H₅N₃O₉) | Liquid | -360.0 |
| Carbon dioxide (CO₂) | Gas | -393.5 |
| Water (H₂O) | Gas | -241.8 |
| Nitrogen (N₂) | Gas | 0.0 |
| Oxygen (O₂) | Gas | 0.0 |
Using the formula:
ΔH = [3(-393.5) + 3(-241.8) + 2(0) + ½(0)] - (-360.0)
ΔH = [-1180.5 - 725.4 + 0 + 0] - (-360.0)
ΔH = -1905.9 + 360.0
ΔH = -1545.9 kJ/mol
The calculation shows that the decomposition of 1 mole of nitroglycerine releases 1545.9 kJ of energy.
Interpreting Results
The negative value for ΔH indicates that the reaction is exothermic, meaning it releases heat to the surroundings. This is characteristic of explosive decomposition reactions.
The large magnitude of the enthalpy change (1545.9 kJ/mol) explains why nitroglycerine is so dangerous - it releases a tremendous amount of energy when it decomposes.
Note: The actual enthalpy change may vary slightly depending on the specific conditions and the source of thermodynamic data used.
FAQ
What is the standard enthalpy change for nitroglycerine decomposition?
The standard enthalpy change for the decomposition of nitroglycerine is approximately -1545.9 kJ/mol, indicating a highly exothermic reaction.
Why is nitroglycerine decomposition so dangerous?
Nitroglycerine decomposition releases a large amount of energy (1545.9 kJ/mol) as heat, which can cause rapid expansion and explosive pressure buildup.
What are the main products of nitroglycerine decomposition?
The main products are carbon dioxide, water vapor, nitrogen gas, and oxygen gas, as shown in the decomposition equation.