Calculate the Rate Constant

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Rate Constant Calculator (Arrhenius Equation)

Frequency of collisions and orientation factor (same units as k).
kJ/mol J/mol
Kelvin (K) Celsius (°C)
Calculated Rate Constant (k):

Understanding the Rate Constant

In chemical kinetics, the rate constant (k) is a proportionality constant that links the molar concentrations of reactants to the reaction rate. While the concentration of reactants changes as the reaction progresses, the rate constant remains steady for a given reaction at a specific temperature.

The Arrhenius Equation Formula

This calculator uses the Arrhenius Equation to determine the rate constant based on temperature and activation energy:

k = A * e^(-Ea / (R * T))
  • k: The Rate Constant.
  • A: The Pre-exponential factor (frequency factor).
  • Ea: Activation Energy (the minimum energy required for a reaction to occur).
  • R: The Universal Gas Constant (8.314 J/mol·K).
  • T: Absolute Temperature (in Kelvin).

Step-by-Step Calculation Example

Suppose you have a reaction with the following parameters:

  • Pre-exponential factor (A): 1.0 × 1013 s-1
  • Activation Energy (Ea): 100 kJ/mol (100,000 J/mol)
  • Temperature (T): 300 K

Step 1: Identify the gas constant (R = 8.314 J/mol·K).
Step 2: Calculate the exponent: -100,000 / (8.314 * 300) = -40.09.
Step 3: Calculate e-40.09 ≈ 3.88 × 10-18.
Step 4: Multiply by A: (1.0 × 1013) * (3.88 × 10-18) = 3.88 × 10-5 s-1.

Key Factors Affecting the Rate Constant

  1. Temperature: As temperature increases, the kinetic energy of molecules increases, leading to a higher rate constant.
  2. Catalysts: Catalysts provide an alternative pathway with a lower activation energy (Ea), which significantly increases the rate constant.
  3. Nature of Reactants: Different chemical bonds and molecular orientations result in vastly different values for A and Ea.
function calculateRateConstant() { var A = parseFloat(document.getElementById('preFactor').value); var EaInput = parseFloat(document.getElementById('activationEnergy').value); var eaUnit = document.getElementById('eaUnit').value; var tempInput = parseFloat(document.getElementById('temperature').value); var tempUnit = document.getElementById('tempUnit').value; var R = 8.314462618; // Gas constant in J/(mol·K) // Validation if (isNaN(A) || isNaN(EaInput) || isNaN(tempInput)) { alert("Please enter valid numerical values for all fields."); return; } // Convert Ea to Joules var Ea = EaInput; if (eaUnit === "kJ") { Ea = EaInput * 1000; } // Convert Temperature to Kelvin var T = tempInput; if (tempUnit === "C") { T = tempInput + 273.15; } if (T <= 0) { alert("Temperature must be greater than absolute zero."); return; } // Arrhenius Logic: k = A * exp(-Ea / (R * T)) var exponent = -Ea / (R * T); var k = A * Math.exp(exponent); // Display Result var resultDiv = document.getElementById('rateResult'); var display = document.getElementById('kValueDisplay'); resultDiv.style.display = 'block'; // Formatting for scientific notation if very small or large if (k 10000) { display.innerHTML = k.toExponential(4); } else { display.innerHTML = k.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 6}); } }

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