Molar Mass of Gas
Molar mass of a gas can be determined from the ideal gas law: PV=nRT. Rearranging gives M = dRT/P where d is density. Used to identify unknown gases and calculate gas density.
Why This Chemistry Calculation Matters
Why: Identifying unknown gases requires molar mass. The ideal gas law lets you measure mass, volume, P, T and compute M. Essential for lab gas identification.
How: From PV=nRT and n=m/M: M = mRT/(PV). For density: ρ = PM/(RT), so M = ρRT/P. Use consistent units (R = 0.08206 L·atm/(mol·K)).
- ●M = mRT/(PV) from ideal gas law; n = PV/RT, M = m/n.
- ●ρ = PM/(RT) for gas density at given P and T.
- ●STP: 1 atm, 273.15 K; Vm ≈ 22.4 L/mol.
Compact Examples
Calculation Mode
Molar Mass Calculation Inputs
Educational Content
What is Molar Mass of a Gas?
The molar mass of a gas is the mass of one mole of that gas, expressed in grams per mole (g/mol). It can be determined experimentally using the ideal gas law when the mass, volume, pressure, and temperature of a gas sample are known. This is particularly useful for identifying unknown gases in laboratory settings.
How to Calculate Molar Mass from Ideal Gas Law
The ideal gas law is PV = nRT, where:
- P = pressure
- V = volume
- n = number of moles
- R = gas constant
- T = temperature (in Kelvin)
Since n = m/M (where m is mass and M is molar mass), we can rearrange:
M = (mRT) / (PV)
Gas Density Formula
Gas density can be calculated from molar mass using:
where ρ is density, P is pressure, M is molar mass, R is the gas constant, and T is temperature.
Standard Conditions
| Condition | Temperature | Pressure | Molar Volume |
|---|---|---|---|
| STP (Standard Temperature and Pressure) | 0°C (273.15 K) | 1 atm (101.325 kPa) | 22.414 L/mol |
| SATP (Standard Ambient Temperature and Pressure) | 25°C (298.15 K) | 1 bar (100 kPa) | 24.789 L/mol |
| NTP (Normal Temperature and Pressure) | 20°C (293.15 K) | 1 atm (101.325 kPa) | 24.055 L/mol |
When to Use This Calculator
- Gas Identification: Determine the identity of an unknown gas by calculating its molar mass
- Stoichiometry: Calculate gas quantities needed for chemical reactions
- Density Calculations: Find gas density at specific conditions
- Laboratory Work: Verify gas purity and composition
- Educational Purposes: Understand ideal gas law applications
Important Notes
• The ideal gas law assumes gases behave ideally (no intermolecular forces, negligible volume)
• Real gases deviate from ideal behavior at high pressures and low temperatures
• Always use absolute temperature (Kelvin) in calculations
• Ensure consistent units throughout calculations
📚 Official Data Sources
⚠️ Disclaimer: This calculator uses the ideal gas law (PV=nRT) and CODATA gas constant. For precise work, consult NIST Chemistry WebBook for gas properties, IUPAC Gold Book for molar mass definitions, and CODATA for the universal gas constant. Ideal gas assumptions may not hold at high pressures or low temperatures.
⚠️For educational and informational purposes only. Verify with a qualified professional.
🔬 Chemistry Facts
M = mRT/(PV) derives from n = PV/RT and M = m/n.
— Ideal gas law
R = 0.08206 L·atm/(mol·K) or 8.314 J/(mol·K).
— CODATA
H₂ = 2.016 g/mol; CO₂ = 44.01 g/mol at STP.
— NIST
Always use Kelvin for T in ideal gas calculations.
— IUPAC
📋 Key Takeaways
- • M = mRT/(PV) | Molar mass from ideal gas law
- • ρ = PM/(RT) | Gas density from molar mass
- • STP: 1 atm, 273.15 K; Vm = 22.4 L/mol
- • SATP: 1 bar, 298.15 K; Vm = 24.8 L/mol
Did You Know?
M = mRT/(PV) from n = PV/(RT) and M = m/n.
Source: Ideal gas law
H₂ = 2.016 g/mol; CO₂ = 44.01 g/mol.
Source: Known gases
R = 0.08206 L·atm/(mol·K) or 8.314 J/(mol·K).
Source: CODATA
Use Kelvin for T in ideal gas law.
Source: Units
Identify unknown gas by comparing M to known gases.
Source: Lab
ρ = PM/(RT) for gas density.
Source: Density
How the Molar Mass of Gas Calculator Works
Enter mass, volume, P, T. M = mRT/(PV). Or enter M, P, T for density. Supports STP, SATP, NTP.
Molar Mass
M = mRT/(PV)
Density
ρ = PM/(RT)
Expert Tips
Units
Match R to P, V, T units.
Presets
STP, SATP, NTP auto-fill P, T.
Identify
Compare M to known gas database.
Ideal
Assumes ideal gas behavior.
Standard Conditions
| Condition | P | T | Vm (L/mol) |
|---|---|---|---|
| STP | 1 atm | 273.15 K | 22.414 |
| SATP | 1 bar | 298.15 K | 24.789 |
| NTP | 1 atm | 293.15 K | 24.055 |
FAQ
How to find molar mass of gas?
M = mRT/(PV). Measure m, V, P, T; use ideal gas law.
What is STP?
1 atm, 273.15 K (0°C). Vm = 22.4 L/mol.
Gas density formula?
ρ = PM/(RT).
R value?
0.08206 L·atm/(mol·K) or 8.314 J/(mol·K).
Ideal gas assumption?
Low P, high T. Real gases deviate.
Identify unknown gas?
Compare calculated M to known gas database.
Key Numbers
📚 Official Sources
⚠️ Disclaimer: Uses ideal gas law. Consult NIST for real gas data.