Understanding the order of a chemical reaction is crucial for predicting how the reaction rate changes with the concentration of reactants. The rate law expresses the relationship between the reaction rate and the concentrations of reactants. For a general reaction:
aA + bB → Products
The rate law is typically written as:
Rate = k[A]x[B]y
where:
'Rate' is the speed of the reaction.
'k' is the rate constant.
'[A]' and '[B]' are the molar concentrations of reactants A and B.
'x' and 'y' are the orders of the reaction with respect to reactants A and B, respectively. These orders are determined experimentally and are not necessarily equal to the stoichiometric coefficients 'a' and 'b'.
This calculator helps determine the order of a reaction with respect to a single reactant, assuming other reactant concentrations are held constant or are not involved in determining the order of the reactant in question.
function calculateRateOrder() {
var initialConcentration = parseFloat(document.getElementById("initialConcentration").value);
var initialRate = parseFloat(document.getElementById("initialRate").value);
var doubledConcentration = parseFloat(document.getElementById("doubledConcentration").value);
var doubledRate = parseFloat(document.getElementById("doubledRate").value);
var resultDiv = document.getElementById("result");
resultDiv.innerHTML = ""; // Clear previous results
if (isNaN(initialConcentration) || isNaN(initialRate) || isNaN(doubledConcentration) || isNaN(doubledRate) ||
initialConcentration <= 0 || doubledConcentration <= 0 || initialRate < 0 || doubledRate < 0) {
resultDiv.innerHTML = "Please enter valid positive numbers for concentrations and non-negative numbers for rates.";
return;
}
// The relationship we are using is:
// Rate2 / Rate1 = (k * [Conc2]^x) / (k * [Conc1]^x)
// Rate2 / Rate1 = ([Conc2] / [Conc1])^x
// We are given that [Conc2] is double [Conc1], so [Conc2] / [Conc1] = 2.
// Rate2 / Rate1 = 2^x
var concentrationRatio = doubledConcentration / initialConcentration;
var rateRatio = doubledRate / initialRate;
if (concentrationRatio <= 0 || rateRatio <= 0) {
resultDiv.innerHTML = "Concentration ratio and rate ratio must be positive for calculation.";
return;
}
// To solve for x, we use logarithms:
// log(Rate2 / Rate1) = x * log(Conc2 / Conc1)
// x = log(Rate2 / Rate1) / log(Conc2 / Conc1)
// If the concentration is doubled, Conc2/Conc1 = 2
// x = log(Rate2 / Rate1) / log(2)
var reactionOrder = Math.log(rateRatio) / Math.log(concentrationRatio);
// Check for common integer orders for clarity in output
var roundedOrder = Math.round(reactionOrder * 100) / 100; // Round to two decimal places
var orderDescription = "";
if (Math.abs(roundedOrder – 0) < 0.05) {
orderDescription = "Zero-order reaction";
} else if (Math.abs(roundedOrder – 1) < 0.05) {
orderDescription = "First-order reaction";
} else if (Math.abs(roundedOrder – 2) < 0.05) {
orderDescription = "Second-order reaction";
} else if (Math.abs(roundedOrder – 3) < 0.05) {
orderDescription = "Third-order reaction";
} else {
orderDescription = "Reaction order";
}
resultDiv.innerHTML = "The calculated order of the reaction with respect to the reactant is: " + roundedOrder + ". This suggests a " + orderDescription + ".";
}