function calculateRateConstant() {
var rate = parseFloat(document.getElementById('reactionRate').value);
var concA = parseFloat(document.getElementById('concA').value);
var orderA = parseFloat(document.getElementById('orderA').value);
var concB_raw = document.getElementById('concB').value;
var orderB_raw = document.getElementById('orderB').value;
if (isNaN(rate) || isNaN(concA) || isNaN(orderA)) {
alert("Please enter values for the Reaction Rate, Concentration A, and Order A.");
return;
}
var concB = concB_raw === "" ? 1 : parseFloat(concB_raw);
var orderB = orderB_raw === "" ? 0 : parseFloat(orderB_raw);
var denominator = Math.pow(concA, orderA) * Math.pow(concB, orderB);
if (denominator === 0) {
alert("Calculation error: Denominator cannot be zero. Ensure concentrations are greater than zero.");
return;
}
var k = rate / denominator;
var overallOrder = orderA + orderB;
var unitStr = "";
if (overallOrder === 0) { unitStr = "M/s"; }
else if (overallOrder === 1) { unitStr = "s⁻¹"; }
else if (overallOrder === 2) { unitStr = "M⁻¹s⁻¹"; }
else if (overallOrder === 3) { unitStr = "M⁻²s⁻¹"; }
else { unitStr = "M^(1-" + overallOrder + ")s⁻¹"; }
document.getElementById('rateResult').style.display = "block";
document.getElementById('kValueDisplay').innerHTML = "k = " + k.toExponential(4);
document.getElementById('unitDisplay').innerHTML = "Units: " + unitStr;
document.getElementById('overallOrderDisplay').innerHTML = "Overall Reaction Order: " + overallOrder;
}
Understanding the Rate Constant (k)
In chemical kinetics, the rate constant k is a proportionality constant that relates the molar concentration of reactants to the rate of a chemical reaction. Every chemical reaction has a unique rate constant that depends on temperature, catalysts, and the specific nature of the reactants.
The Rate Law Formula
The general form of a rate law for a reaction involving two reactants (A and B) is:
Rate = k [A]m [B]n
Where:
Rate: The speed of the reaction (usually in mol/L·s).
k: The rate constant.
[A], [B]: The molar concentrations of the reactants.
m, n: The partial orders of reaction (determined experimentally).
Example Calculation
Suppose you have a first-order reaction where the initial rate is 0.02 M/s and the concentration of reactant [A] is 0.5 M.
Rate: 0.02
[A]: 0.5
Order (m): 1
Formula: k = Rate / [A]1
Result: k = 0.02 / 0.5 = 0.04 s⁻¹
Units of k
The units of the rate constant change depending on the overall reaction order (m + n):
Overall Order
Units of k
0
M/s (or mol·L⁻¹·s⁻¹)
1
s⁻¹
2
M⁻¹s⁻¹ (or L·mol⁻¹·s⁻¹)
3
M⁻²s⁻¹ (or L²·mol⁻²·s⁻¹)
Temperature and k
It is important to note that while the rate constant is "constant" for a specific reaction at a fixed temperature, it increases as temperature rises. This relationship is described by the Arrhenius Equation: k = Ae-Ea/RT, where A is the frequency factor and Ea is the activation energy.