Enter the molar mass of the substance (e.g., Water ≈ 18.02 g/mol, Oxygen ≈ 32.00 g/mol).
Results
Molar Flow Rate (mol/s):–
Molar Flow Rate (mol/h):–
Molar Flow Rate (kmol/h):–
Pound-mole Rate (lb-mol/h):–
About Molar Flow Rate
The Molar Flow Rate is a fundamental concept in chemical engineering and process chemistry. It represents the amount of substance (measured in moles) that flows past a specific cross-section per unit of time. Unlike mass flow rate, which measures the mass moving through a system, molar flow rate focuses on the number of chemical units (atoms or molecules), which is essential for stoichiometry calculations in chemical reactors.
The Formula
The calculation is derived from the Mass Flow Rate and the Molar Mass of the substance. The fundamental equation is:
ṅ = ṁ / M
Where:
ṅ (n-dot) = Molar Flow Rate (moles per time unit)
ṁ (m-dot) = Mass Flow Rate (mass per time unit)
M = Molar Mass (mass per mole)
How to Calculate Molar Flow Rate
Determine the Mass Flow Rate: Measure or identify the rate at which mass is moving (e.g., 50 grams per second).
Identify the Molar Mass: Find the molar mass of the substance from the periodic table. For example, Water ($H_2O$) is approximately 18.015 g/mol.
Ensure Unit Consistency: Convert your mass flow rate to grams per unit time if your molar mass is in g/mol.
Divide: Divide the mass flow rate by the molar mass to get the molar flow rate.
Example Calculation
Imagine water is flowing through a pipe at a rate of 10 kg/minute. You want to know the molar flow rate in mol/s.
Substance: Water ($H_2O$)
Molar Mass ($M$): 18.015 g/mol
Mass Flow Rate ($ṁ$): 10 kg/min
Step 1: Convert Mass Flow to g/s
10 kg/min = 10,000 g/min = (10,000 / 60) g/s ≈ 166.67 g/s.
Chemical Reactors: Balancing chemical equations happens in moles, not mass. Engineers need molar flow rates to ensure reactants enter in the correct stoichiometric ratios.
Separation Processes: Distillation and absorption column designs rely on molar flows to determine efficiency.
Environmental Engineering: Tracking the molar flow of pollutants in flue gases.
function calculateMolarFlow() {
// Get inputs
var massFlowInput = document.getElementById('massFlowRate').value;
var unitInput = document.getElementById('massFlowUnit').value;
var molarMassInput = document.getElementById('molarMass').value;
// Get Elements for display
var errorDiv = document.getElementById('errorDisplay');
var resultDiv = document.getElementById('resultSection');
var resMolS = document.getElementById('resMolS');
var resMolH = document.getElementById('resMolH');
var resKmolH = document.getElementById('resKmolH');
var resLbMolH = document.getElementById('resLbMolH');
// Reset state
errorDiv.style.display = 'none';
resultDiv.style.display = 'none';
// Validation
if (massFlowInput === "" || molarMassInput === "") {
errorDiv.innerText = "Please enter both Mass Flow Rate and Molar Mass.";
errorDiv.style.display = 'block';
return;
}
var mDot = parseFloat(massFlowInput);
var M = parseFloat(molarMassInput);
if (isNaN(mDot) || isNaN(M)) {
errorDiv.innerText = "Please enter valid numerical values.";
errorDiv.style.display = 'block';
return;
}
if (M <= 0) {
errorDiv.innerText = "Molar Mass must be greater than zero.";
errorDiv.style.display = 'block';
return;
}
if (mDot < 0) {
errorDiv.innerText = "Mass Flow Rate cannot be negative.";
errorDiv.style.display = 'block';
return;
}
// Step 1: Normalize Mass Flow Rate to g/s (grams per second)
// Molar mass is usually g/mol, so g/s is the easiest intermediate unit for mol/s
var massFlowInGramsPerSec = 0;
switch(unitInput) {
case 'kg_s': // kg/s to g/s
massFlowInGramsPerSec = mDot * 1000;
break;
case 'g_s': // g/s to g/s
massFlowInGramsPerSec = mDot;
break;
case 'kg_h': // kg/h to g/s
// 1 kg = 1000g, 1 hr = 3600s
massFlowInGramsPerSec = (mDot * 1000) / 3600;
break;
case 'lb_h': // lb/h to g/s
// 1 lb = 453.59237 g, 1 hr = 3600s
massFlowInGramsPerSec = (mDot * 453.59237) / 3600;
break;
case 'lb_s': // lb/s to g/s
massFlowInGramsPerSec = mDot * 453.59237;
break;
default:
massFlowInGramsPerSec = mDot;
}
// Step 2: Calculate Molar Flow Rate in mol/s
// Formula: n_dot = m_dot (g/s) / M (g/mol)
var molPerSec = massFlowInGramsPerSec / M;
// Step 3: Convert to other output units
// mol/h
var molPerHour = molPerSec * 3600;
// kmol/h (1 kmol = 1000 mol)
var kmolPerHour = molPerHour / 1000;
// lb-mol/h
// 1 lb-mol = 453.59237 mol
var lbMolPerHour = molPerHour / 453.59237;
// Display Results
// Using 4 decimal places for precision, or 6 if very small
resMolS.innerText = molPerSec < 0.001 && molPerSec !== 0 ? molPerSec.toExponential(4) : molPerSec.toFixed(4);
resMolH.innerText = molPerHour < 0.001 && molPerHour !== 0 ? molPerHour.toExponential(4) : molPerHour.toFixed(2);
resKmolH.innerText = kmolPerHour < 0.001 && kmolPerHour !== 0 ? kmolPerHour.toExponential(4) : kmolPerHour.toFixed(4);
resLbMolH.innerText = lbMolPerHour < 0.001 && lbMolPerHour !== 0 ? lbMolPerHour.toExponential(4) : lbMolPerHour.toFixed(4);
resultDiv.style.display = 'block';
}