The rate of a chemical reaction describes how quickly reactants are consumed or products are formed over time. It's typically measured in units of concentration per unit time, such as moles per liter per second (mol/L/s).
For a general reaction involving reactants A and B:
aA + bB → Products
The rate law often takes the form:
Rate = k[A]^m [B]^n
Where:
Rate is the reaction rate.
k is the rate constant, which is specific to the reaction and temperature.
[A] and [B] are the molar concentrations of reactants A and B.
m and n are the reaction orders with respect to A and B, respectively. These are experimentally determined and do not necessarily equal the stoichiometric coefficients (a and b).
This calculator allows you to compute the instantaneous rate using initial concentrations and the rate constant. It can also estimate the average rate if you provide a time interval and the change in concentration of a reactant over that interval.
Instantaneous Rate Calculation:
If you provide the initial concentrations of reactants, their respective reaction orders, and the rate constant (k), the calculator will compute the initial instantaneous rate using the formula: Rate = k[A]^m [B]^n
Average Rate Calculation:
If you provide a time interval and the change in concentration of a reactant (e.g., A) over that interval (Δ[A]), the calculator can estimate the average rate using: Average Rate = -Δ[A] / Δt (where Δt is the time interval). The negative sign indicates the consumption of a reactant.
function calculateReactionRate() {
var initialConcentrationA = parseFloat(document.getElementById("initialConcentrationA").value);
var initialConcentrationB = parseFloat(document.getElementById("initialConcentrationB").value);
var reactionOrderA = parseFloat(document.getElementById("reactionOrderA").value);
var reactionOrderB = parseFloat(document.getElementById("reactionOrderB").value);
var rateConstant = parseFloat(document.getElementById("rateConstant").value);
var timeInterval = parseFloat(document.getElementById("timeInterval").value);
var finalConcentrationA = parseFloat(document.getElementById("finalConcentrationA").value);
var resultDiv = document.getElementById("result");
var resultHTML = "";
// Input validation
var isValidInstantaneous = !isNaN(initialConcentrationA) && !isNaN(initialConcentrationB) && !isNaN(reactionOrderA) && !isNaN(reactionOrderB) && !isNaN(rateConstant);
var isValidAverage = !isNaN(timeInterval) && !isNaN(finalConcentrationA) && !isNaN(initialConcentrationA);
if (isValidInstantaneous) {
var instantaneousRate = rateConstant * Math.pow(initialConcentrationA, reactionOrderA) * Math.pow(initialConcentrationB, reactionOrderB);
if (!isNaN(instantaneousRate)) {
resultHTML += "Instantaneous Rate (at t=0): " + instantaneousRate.toFixed(5) + " mol/L/s";
}
} else {
resultHTML += "Please provide valid values for initial concentrations, reaction orders, and rate constant to calculate instantaneous rate.";
}
if (isValidAverage && !isNaN(timeInterval) && timeInterval > 0) {
var deltaConcentrationA = finalConcentrationA – initialConcentrationA;
var averageRate = -deltaConcentrationA / timeInterval;
if (!isNaN(averageRate)) {
resultHTML += "Average Rate over " + timeInterval + " s: " + averageRate.toFixed(5) + " mol/L/s";
}
} else if (isValidAverage && timeInterval <= 0) {
resultHTML += "Time interval for average rate must be positive.";
}
if (resultHTML === "") {
resultDiv.innerHTML = "Please enter valid inputs for calculation.";
} else {
resultDiv.innerHTML = resultHTML;
}
}