Calculator Inputs
Page sections stay stacked in one column, while the form fields adapt across large, medium, and mobile screens.
Formula Used
1) Arrhenius temperature correction
k(T) = A × e−Ea / RT
2) Effective reaction constant
keff = k(T) × Fsolvent × Fleaving × Fsteric × Fcatalyst
3) General substitution rate law
Rate = keff × [RX]m × [Nu]n
4) Observed substrate decay constant
kobs = keff × [Nu]n
5) Time models used for conversion
- Zero-order in substrate: [RX]t = [RX]0 − kobst
- First-order in substrate: [RX]t = [RX]0e−kobst
- Second-order in substrate: [RX]t = [RX]0 / (1 + kobs[RX]0t)
Typical mechanistic defaults are SN1: m = 1, n = 0 and SN2: m = 1, n = 1. The adjustment factors are practical multipliers for comparing conditions when complete mechanistic constants are unavailable.
How to Use This Calculator
- Choose SN1, SN2, or Custom based on your mechanistic assumption.
- Enter the pre-exponential factor, activation energy, and reaction temperature.
- Fill in substrate and nucleophile concentrations with consistent units.
- Set rate orders and correction factors for solvent, leaving group, sterics, and catalyst effects.
- Enter the reaction time, then press Calculate Rate.
- Read the result panel above the form for constants, rate, conversion, and half-life.
- Review the Plotly graph to see temperature sensitivity.
- Use the CSV or PDF buttons to export your report.
Example Data Table
| Case | Mechanism | Temperature (°C) | keff | Initial Rate (mol L⁻¹ s⁻¹) | Conversion (%) |
|---|---|---|---|---|---|
| Example A | SN1 | 35 | 0.056039 | 0.005604 | 100.00 % |
| Example B | SN2 | 25 | 0.008083 | 2.4249e-4 | 83.78 % |
| Example C | CUSTOM | 45 | 0.15403 | 0.005305 | 100.00 % |
These sample rows are generated from the same model used by the calculator, so the example outputs stay consistent with the live formula logic.
FAQs
1) What mechanism should I choose?
Select SN1 when rate mainly depends on substrate ionization in polar protic media. Select SN2 when nucleophile attack and substrate concentration jointly control rate, especially for less hindered substrates in polar aprotic solvents.
2) Why can SN1 ignore nucleophile concentration?
SN1’s slow step is carbocation formation. Because nucleophile capture happens later, changing nucleophile concentration usually does not control the measured rate under standard kinetic assumptions.
3) What units should the pre-exponential factor use?
Use units consistent with your overall rate law. First-order models use s⁻¹, while second-order models often use L·mol⁻¹·s⁻¹. Keep concentration units consistent across every input.
4) Why does temperature change rate so sharply?
Temperature enters the Arrhenius term exponentially. Even modest heating can raise the fraction of molecules exceeding activation energy, making the predicted constant and rate increase quickly.
5) What do the adjustment factors represent?
Solvent, leaving-group, steric, and catalyst factors scale the base Arrhenius rate. They are practical multipliers for comparing scenarios when detailed mechanistic constants are unavailable.
6) When is the conversion estimate most reliable?
Conversion is strongest when the chosen integrated order matches the experiment and nucleophile concentration stays effectively constant. For complex multi-step systems, treat it as a screening estimate.
7) Can I use custom reaction orders?
Yes. The initial-rate calculation supports custom orders. Time-profile outputs are fully shown for zero-, first-, and second-order substrate dependence, because those integrated forms are straightforward.
8) What does the graph show?
The graph plots predicted initial rate across a temperature window while holding concentrations and adjustment factors fixed. It highlights Arrhenius sensitivity and helps compare operating conditions visually.