Rate Law Equation Calculator

Determine the reaction rate based on the rate constant, reactant concentrations, and reaction orders.

Resulting Rate:

function calculateRateLaw() { var k = parseFloat(document.getElementById('rateConstant').value); var a = parseFloat(document.getElementById('concA').value); var m = parseFloat(document.getElementById('orderA').value); var bInput = document.getElementById('concB').value; var nInput = document.getElementById('orderB').value; if (isNaN(k) || isNaN(a) || isNaN(m)) { alert("Please enter at least the Rate Constant, Concentration [A], and Order of [A]."); return; } var rate; var b = (bInput === "" || isNaN(parseFloat(bInput))) ? 1 : parseFloat(bInput); var n = (nInput === "" || isNaN(parseFloat(nInput))) ? 0 : parseFloat(nInput); // Calculation: Rate = k * [A]^m * [B]^n rate = k * Math.pow(a, m) * Math.pow(b, n); var resultDiv = document.getElementById('rateResult'); var output = document.getElementById('rateOutput'); var formula = document.getElementById('formulaOutput'); resultDiv.style.display = 'block'; // Format scientific notation for very small/large numbers if (rate 1000) { output.innerHTML = rate.toExponential(4) + " M/s"; } else { output.innerHTML = rate.toFixed(6) + " M/s"; } var formulaString = "Calculation: " + k + " × (" + a + ")^{" + m + "}"; if (bInput !== "" && !isNaN(parseFloat(bInput))) { formulaString += " × (" + b + ")^{" + n + "}"; } formula.innerHTML = formulaString; }

Understanding the Rate Law Equation

The rate law is a mathematical expression that describes the relationship between the speed of a chemical reaction and the concentration of its reactants. In chemical kinetics, the rate of reaction is generally proportional to the product of the concentrations of the reactants, each raised to a specific power known as the "order" of the reactant.

The Basic Formula

Rate = k [A]^m [B]ⁿ

• Rate: The speed of the reaction, typically measured in Molarity per second (M/s).
• k: The rate constant, which is specific to a particular reaction at a specific temperature.
• [A], [B]: The molar concentrations of the reactants (M).
• m, n: The partial orders of the reaction with respect to reactant A and B.

How to Use This Calculator

To use the rate law equation calculator, follow these steps:

1. Enter the Rate Constant (k): This is usually determined experimentally or given in your problem set. Pay attention to the units of k, as they change depending on the overall order.
2. Input Concentration of [A]: Enter the molarity (mol/L) of your first reactant.
3. Set the Order (m): This is the exponent for [A]. If the rate doubles when concentration doubles, the order is 1 (first order). If the rate quadruples, the order is 2 (second order).
4. Add Reactant [B] (Optional): If your reaction has a second reactant, input its concentration and order. If not, leave these fields blank or set the order to 0.
5. Click Calculate: The tool will output the reaction rate in M/s.

Example Calculation

Consider a reaction where k = 0.02 M^-1s^-1, [A] = 0.5 M (first order), and [B] = 0.2 M (first order).

The rate law is: Rate = 0.02 × [0.5]1 × [0.2]1

Step 1: 0.5¹ = 0.5

Step 2: 0.2¹ = 0.2

Step 3: Rate = 0.02 × 0.5 × 0.2 = 0.002 M/s.

Units of the Rate Constant (k)

The units for the rate constant k depend on the overall order of the reaction (sum of m + n):

Overall Order	Units of k
0 (Zero Order)	M/s or M · s^-1
1 (First Order)	s^-1 (1/s)
2 (Second Order)	M^-1 · s^-1 (L/mol·s)
3 (Third Order)	M^-2 · s^-1 (L^2/mol^2·s)