STP Calculator

Convert gas volumes to standard temperature and pressure (0°C, 1 atm), calculate moles, density, and molar mass. The molar volume of an ideal gas at STP is 22.414 L/mol.

Volume of gas at given conditions

Temperature of the gas

Pressure of the gas in atmospheres

Mass of the gas sample in grams

Molar mass of the gas

Standard Temperature and Pressure: STP Conditions: • Temperature = 0°C (273.15 K) • Pressure = 1 atm (101.325 kPa) • Molar Volume = 22.414 L/mol Combined Gas Law: V_STP = V × (P / P_STP) × (T_STP / T) Where: • V_STP = Volume at STP (L) • V = Volume at given conditions (L) • P = Pressure at given conditions (atm) • P_STP = Standard pressure = 1 atm • T_STP = Standard temperature = 273.15 K • T = Temperature at given conditions (K) Converting to Kelvin: K = °C + 273.15 Moles from Volume at STP: n = V_STP / 22.414 Moles from Mass: n = mass / molar mass Density at STP: ρ = molar mass / 22.414
Example 1: Volume Correction to STP 5.0 L of oxygen collected at 25°C and 1.5 atm V_STP = 5.0 × (1.5/1.0) × (273.15/298.15) V_STP = 6.87 L Moles = 6.87 / 22.414 = 0.306 mol O₂ Example 2: Moles from Volume at STP What volume does 2.0 mol of N₂ occupy at STP? V = 2.0 × 22.414 = 44.83 L Example 3: Density of CO₂ at STP Molar mass of CO₂ = 44.01 g/mol Density = 44.01 / 22.414 = 1.964 g/L Density relative to air = 1.964/1.292 = 1.52 CO₂ is 52% denser than air Example 4: Molar Mass Determination 0.500 g of unknown gas occupies 0.280 L at STP Moles = 0.280 / 22.414 = 0.01249 mol Molar mass = 0.500 / 0.01249 = 40.03 g/mol This matches argon (39.95 g/mol) Common Gas Densities at STP: • H₂: 0.0899 g/L • He: 0.1785 g/L • N₂: 1.251 g/L • Air: 1.292 g/L • O₂: 1.429 g/L • CO₂: 1.964 g/L

What are standard temperature and pressure (STP)?

STP is defined as 0°C (273.15 K) and 1 atmosphere (101.325 kPa) of pressure. At these conditions, one mole of any ideal gas occupies exactly 22.414 liters. This standard allows scientists to compare gas volumes and calculate molar quantities consistently, regardless of ambient conditions.

How do I convert gas volume to STP conditions?

Use the combined gas law: V_STP = V × (P/P_STP) × (T_STP/T), where T must be in Kelvin (K = °C + 273.15). For example, if 5.0 L of gas at 25°C and 1.5 atm is brought to STP: V_STP = 5.0 × (1.5/1.0) × (273.15/298.15) = 6.87 L. This accounts for both temperature and pressure changes.

What is the difference between STP, NTP, and SATP?

STP (Standard Temperature and Pressure) is 0°C and 1 atm, giving a molar volume of 22.414 L/mol. NTP (Normal Temperature and Pressure) is 20°C and 1 atm, with molar volume 24.055 L/mol. SATP (Standard Ambient Temperature and Pressure) is 25°C and 1 bar (0.987 atm), with molar volume 24.79 L/mol. Always note which standard is being used.

When does the ideal gas law break down at STP?

The ideal gas law assumes no intermolecular forces and negligible molecular volume. Real gases deviate from ideal behavior, especially at high pressure or low temperature. At STP, most common gases (O₂, N₂, H₂, noble gases) behave nearly ideally. However, gases like NH₃, SO₂, and polar molecules show slight deviations even at STP due to intermolecular attractions.

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