Key Difference – STP vs Standard Molar Volume
The term STP stands for Standard Temperature and Pressure. The IUPAC gives 273.15 K (0°C or 32°F) as the standard temperature and 10^{5} Pa (1.00 atom or 1 bar) as the standard pressure. The standard molar volume is the volume of a mole of a substance at standard temperature and pressure. For an ideal gas, the standard molar volume is 22.4 L/mol. The key difference between STP and standard molar volume is that STP gives temperature by the unit K (Kelvin) and pressure by Pa (Pascal) whereas standard molar volume is given by L/mol (Liters per mole) unit.
CONTENTS
1. Overview and Key Difference
2. What is STP
3. What is Standard Molar Volume
4. Side by Side Comparison – STP vs Standard Molar Volume in Tabular Form
5. Summary
What is STP?
The term STP stands for standard temperature and pressure. It is the IUPAC definition for STP. This term is often used in relation to the calculations of gases. The molar volume of any gas at STP is 22.4 L/mol. The standard temperature and pressure given by IUPAC in 1982 are as follows.
Standard Temperature: 273.15 K (0°C or 32°F)
Standard Pressure: 10^{5} Pa (1.00 atom or 1 bar)
This is the freezing point of water in its pure state and at sea level. However, the term STP should not be confused with NTP (normal temperature and pressure). NTP is 20 °C (293.15 K, 68 °F) and 1 atm (14.696 psi, 101.325 kPa).
The term STP is often used in calculations such as flow rate of which the value is dependent on the temperature and pressure. And also it is used where standard conditions are considered. It is denoted as a superscript circle; Ex: the entropy of a thermodynamic system at STP is given as ΔS°.
What is Standard Molar Volume?
Standard molar volume is the volume occupied by a mole of a substance at standard temperature and pressure. The substance can be a gas, liquid or a solid. The molar volume is denoted by Vm whereas standard molar volume is denoted by Vm°. The standard molar volume of an ideal gas is 22.4 L/mol.
Standard Molar Volume Calculation
According to the ideal gas law, for an ideal gas,
PV = nRT
In which, P, V, and T are pressure, volume and temperature of the ideal gas and n is the number of moles of the ideal gas present. R is the universal gas constant given as 8.314 JK^{1}mol^{1}(0.08206 L atm mol^{1} K^{1}). The standard temperature and pressure for an ideal gas are 273.15 K and 10^{5} Pa (1.00 atm) respectively.
PV = nRT
(1.00 atm) x Vm° = (1 mol) x (0.08206 L atm mol^{1} K^{1})x (273.15 K)
Vm° = 22.4 L/mol.
The SI unit for the standard molar volume is cubic meters per mole (m^{3}/mol). But it is used as cubic decimeters per mole (dm^{3}/mol) in common uses.
The standard molar volume can also be calculated as below.
Molar volume = Molar mass / Density
There the values should be taken based on the standard temperature and pressure. If the substance has more than one component, the standard molar volume is the sum of standard molar volume values of all those components.
What is the Difference Between STP and Standard Molar Volume?
STP vs Standard Molar Volume 

The term STP stands for standard temperature and pressure.  Standard molar volume is the volume occupied by a mole of a gas at STP. 
Components  
STP describes about temperature and pressure.  The standard molar volume describes the volume. 
Unit(s)  
STP gives temperature by the unit K (Kelvin) and pressure by Pa (Pascal).  Standard molar volume is given by L/mol (Liters per mole) unit. 
Summary – STP vs Standard Molar Volume
STP is the standard temperature and pressure. Standard molar volume is the volume of a mole of a substance at STP. The difference between STP and standard molar volume is that STP gives temperature by the unit K (Kelvin) and pressure by Pa (Pascal) whereas standard molar volume is given by L/mol (Liters per mole) unit.
Reference:
1.Helmenstine, Ph.D. Anne Marie. “Learn What Standard Temperature and Pressure (STP) Means in Chemistry.” ThoughtCo. Available here
2.“Molar volume.” Wikipedia, Wikimedia Foundation, 17 Feb. 2018. Available here
3. Chemistry 31, Molar Volume. Available here
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