Calculate Rate of Disappearance based on Rate of Appearance and Stoichiometry.
The stoichiometric number in front of the reactant in the balanced equation.
The stoichiometric number in front of the product in the balanced equation.
Calculated Rate of Disappearance
0.000 M/s
function calculateKinetics() {
// 1. Get input values
var coeffReactant = parseFloat(document.getElementById('coeffDisappearing').value);
var coeffProduct = parseFloat(document.getElementById('coeffAppearing').value);
var rateAppearing = parseFloat(document.getElementById('rateAppearance').value);
var resultBox = document.getElementById('results');
var finalRateDisplay = document.getElementById('finalRate');
var formulaDisplay = document.getElementById('formulaUsed');
// 2. Validate inputs
if (isNaN(coeffReactant) || coeffReactant <= 0) {
alert("Please enter a valid positive coefficient for the reactant.");
return;
}
if (isNaN(coeffProduct) || coeffProduct <= 0) {
alert("Please enter a valid positive coefficient for the product.");
return;
}
if (isNaN(rateAppearing)) {
alert("Please enter a valid number for the Rate of Appearance.");
return;
}
// 3. Calculation Logic
// Formula: Rate_Disappearance = (Coeff_Reactant / Coeff_Product) * Rate_Appearance
var ratio = coeffReactant / coeffProduct;
var rateDisappearance = ratio * rateAppearing;
// 4. Formatting output (handle float precision)
// Check if the result is an integer, otherwise fix to 4 decimals
var displayRate = Number.isInteger(rateDisappearance) ? rateDisappearance : rateDisappearance.toFixed(6);
// Remove trailing zeros if decimal
displayRate = parseFloat(displayRate);
// 5. Update UI
resultBox.style.display = 'block';
finalRateDisplay.innerHTML = displayRate + " M/s";
formulaDisplay.innerHTML =
"Ratedisappearance = (" + coeffReactant + " / " + coeffProduct + ") × " + rateAppearing + " = " + displayRate;
}
How to Calculate Rate of Disappearance from Rate of Appearance
In chemical kinetics, the speed at which a reaction proceeds is often measured by how fast reactants are consumed (disappearance) or how fast products are formed (appearance). These rates are stoichiometrically linked. This guide and calculator help you convert the known rate of appearance of a product into the rate of disappearance of a reactant using the balanced chemical equation.
General Equation: aA + bB → cC + dD
Understanding the Relationship
The fundamental principle connecting these rates is that the rate of reaction normalized by the stoichiometric coefficient is constant for all species in the reaction. Mathematically, for the equation above:
Rate of Reaction = – (1/a)Δ[A]/Δt = (1/c)Δ[C]/Δt
Where:
a is the coefficient of the reactant (disappearing).
c is the coefficient of the product (appearing).
Δ[A]/Δt is the rate of change of reactant A (negative because it decreases).
Δ[C]/Δt is the rate of change of product C (positive because it increases).
The Conversion Formula
To calculate the rate of disappearance of a reactant directly from the rate of appearance of a product, we isolate the disappearance term. While rates of change for reactants are technically negative, we usually express the "Rate of Disappearance" as a positive magnitude.
Formula:
Rate of Disappearance (Reactant) = (CoefficientReactant / CoefficientProduct) × Rate of Appearance (Product)
Step-by-Step Calculation Example
Let's look at the production of Ammonia via the Haber process:
N2 + 3H2 → 2NH3
Suppose we measure that Ammonia (NH3) is appearing at a rate of 0.060 M/s. We want to find the rate of disappearance of Hydrogen (H2).
Identify Coefficients:
Coefficient of appearing product (NH3) = 2
Coefficient of disappearing reactant (H2) = 3
Identify Known Rate: Rate of Appearance = 0.060 M/s.
Thus, Hydrogen is being consumed at a rate of 0.090 M/s.
Why Does Stoichiometry Matter?
Stoichiometry dictates the mole ratios. In the example above ($N_2 + 3H_2 \rightarrow 2NH_3$), for every 2 moles of ammonia made, 3 moles of hydrogen must be used up. Therefore, hydrogen must disappear 1.5 times faster than ammonia appears (3/2 = 1.5).
Common Applications
Field
Application
Industrial Chemistry
Optimizing production lines by monitoring product formation to estimate raw material consumption.
Pharmacology
Determining how fast a drug precursor is metabolized into the active compound.
Environmental Science
Calculating how quickly pollutants degrade based on the appearance of breakdown byproducts.
Frequently Asked Questions
Why is the rate of disappearance usually positive?
Mathematically, the change in concentration of a reactant ($\Delta[Reactant]$) is negative because the concentration drops over time. However, chemists typically define the "Rate of Disappearance" as the negative of the rate of change ($-\Delta[Reactant]/\Delta t$) to make the value a positive number representing speed.
What units should I use?
The most common unit for reaction rates is Molarity per second (M/s), which is equivalent to mol/(L·s). However, the calculator works with any unit (e.g., mol/min, g/s) as long as the input and output units remain consistent.
Can I use this for non-integers?
Yes. Sometimes chemical equations are balanced with fractions (e.g., $H_2 + \frac{1}{2}O_2 \rightarrow H_2O$). The calculator supports decimal coefficients.