Input Data
Define gaseous species participating in the reaction and specify their stoichiometric coefficients and initial partial pressures. Positive coefficients represent products; negative coefficients represent reactants.
Example Data Table
This example shows typical input values and the corresponding equilibrium results for a hypothetical gas-phase reaction.
| Species | ν | Initial partial pressure (atm) | Equilibrium partial pressure (atm) |
|---|---|---|---|
| A (reactant) | -1 | 1.00 | 0.40 |
| B (reactant) | -1 | 1.00 | 0.40 |
| C (product) | 1 | 0.00 | 1.20 |
Formula Used
For a general gas-phase reaction, the equilibrium constant in terms of partial pressure is written as Kp = ∏ Piνi, where Pi is the partial pressure of species i and νi is its stoichiometric coefficient (positive for products, negative for reactants).
If initial partial pressures are Pi,0 and the reaction extent is x, then the equilibrium partial pressure of each species is Pi = Pi,0 + νix, provided all pressures remain positive. The calculator numerically solves for x so that the calculated Kp matches the specified value.
How to Use This Calculator
- Identify all gaseous species in your balanced chemical reaction.
- Assign negative stoichiometric coefficients to reactants and positive coefficients to products.
- Enter the value of the equilibrium constant Kp at the reaction temperature.
- Specify the initial partial pressure for each gaseous species in atmospheres.
- Leave unused rows blank or with zero stoichiometric coefficients.
- Click the calculate button to compute equilibrium partial pressures and mole fractions.
- Download results as CSV or PDF for reporting or further analysis.
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Equilibrium Partial Pressure Concepts
Equilibrium partial pressure describes the pressure exerted by each gaseous component when a reaction mixture has reached a state of dynamic equilibrium. At equilibrium, forward and reverse reaction rates are equal, so macroscopic pressures remain constant despite continuous molecular-level activity.
The equilibrium constant Kp encodes how strongly products are favored over reactants at a given temperature. Larger Kp values generally correspond to product-favored equilibria, while small Kp values indicate reactant-favored systems. Translating Kp into individual partial pressures is essential for reactor design and safety assessments.
This calculator uses a numerical method to solve the equilibrium condition instead of relying on manual algebra, which becomes challenging for multi-species or non-integer stoichiometries. By directly working with partial pressures, it stays consistent with common thermodynamic data tables and laboratory measurements.
Frequently Asked Questions
1. Which units should I use for partial pressures?
This calculator is set up for atmospheres. If your data uses other units, convert them to atmospheres before entering values to keep Kp interpretation consistent and meaningful.
2. What does a negative stoichiometric coefficient represent?
Negative coefficients correspond to reactants, indicating that their partial pressures decrease as the reaction proceeds toward equilibrium. Positive coefficients represent products, whose pressures increase as equilibrium is approached.
3. Why do I receive an error about bracketing the solution?
The numerical routine needs a range where the equilibrium condition changes sign. If inputs are inconsistent with the given Kp, no valid solution exists within the physically allowed pressure range.
4. Can this calculator handle reactions with more than four gases?
The interface currently supports up to four gaseous species. For more complex systems, group minor species, simplify the mechanism, or perform custom calculations using similar equations in numerical software.
5. How accurate are the computed equilibrium partial pressures?
The underlying algorithm uses a bisection-based numerical method with a strict tolerance. For well-posed problems with realistic input data, the results are more than adequate for teaching, design, and preliminary research.
6. Do temperature changes affect the equilibrium partial pressures?
Yes, temperature influences Kp through the van't Hoff relationship. If temperature changes, recalculate Kp from thermodynamic data or tables, then rerun this calculator with the updated constant for consistent equilibrium predictions.