Organic Chemistry Mechanism Calculator

Organic Chemistry Kinetics & Energetics Calculator

Calculate Reaction Rate (k) and Gibbs Free Energy (ΔG)

Calculation Results:

Rate Constant (k): –
Gibbs Free Energy (ΔG) at T: –
Thermodynamic Feasibility: –

Understanding Organic Chemistry Reaction Mechanisms

In organic chemistry, a mechanism describes the step-by-step sequence of elementary reactions by which overall chemical change occurs. To predict whether a mechanism like SN1, SN2, E1, or E2 will occur, chemists look at the kinetic and thermodynamic barriers.

The Arrhenius Equation & Kinetics

The rate of a mechanism is governed by the Arrhenius equation: k = Ae-Ea/RT. This calculator determines the rate constant (k) based on your activation energy and temperature. In mechanisms like SN2, the transition state involves a high activation energy if the substrate is sterically hindered, significantly lowering the rate constant.

Gibbs Free Energy (ΔG)

While kinetics tell us how fast a reaction happens, thermodynamics tell us if it will happen at all. The Gibbs Free Energy equation, ΔG = ΔH – TΔS, determines spontaneity.

  • Negative ΔG: Exergonic reaction (Spontaneous).
  • Positive ΔG: Endergonic reaction (Non-spontaneous).

Practical Example: SN1 vs SN2

Imagine a tertiary alkyl halide. Because of steric hindrance, the Ea for an SN2 mechanism is extremely high. However, the formation of a stable carbocation in an SN1 mechanism may have a lower Ea for the rate-determining step, making the SN1 path the dominant mechanism at room temperature.

function calculateMechanism() { var ea = parseFloat(document.getElementById("eaInput").value); var tempC = parseFloat(document.getElementById("tempInput").value); var a = parseFloat(document.getElementById("aFactor").value); var deltaS = parseFloat(document.getElementById("entropyInput").value); var R = 8.314; // Gas constant in J/(mol·K) if (isNaN(ea) || isNaN(tempC) || isNaN(a) || isNaN(deltaS)) { alert("Please enter all required values to calculate the mechanism energetics."); return; } // Convert Temperature to Kelvin var T = tempC + 273.15; // 1. Calculate Rate Constant (Arrhenius) // k = A * exp(-Ea / RT). Ea is kJ/mol, so multiply by 1000 for J/mol var exponent = -(ea * 1000) / (R * T); var k = a * Math.exp(exponent); // 2. Calculate Gibbs Free Energy (Simplified for mechanism feasibility) // deltaG = deltaH – T * deltaS. Assuming Ea approximates deltaH for the transition state var deltaG = (ea * 1000) – (T * deltaS); var deltaGkJ = deltaG / 1000; // Display results document.getElementById("resultsArea").style.display = "block"; // Formatting k for scientific notation if (k 1000) { document.getElementById("rateConstant").innerText = k.toExponential(4) + " s⁻¹"; } else { document.getElementById("rateConstant").innerText = k.toFixed(4) + " s⁻¹"; } document.getElementById("gibbsEnergy").innerText = deltaGkJ.toFixed(2) + " kJ/mol"; var feasibilityEl = document.getElementById("feasibility"); if (deltaGkJ < 0) { feasibilityEl.innerText = "Thermodynamically Favored"; feasibilityEl.style.color = "#27ae60"; } else { feasibilityEl.innerText = "Non-Spontaneous / High Barrier"; feasibilityEl.style.color = "#c0392b"; } }

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