NTP and STP

1. STP (Standard Temperature and Pressure)

  a. standard reference of temperature and pressure commonly used in chemistry and phyiscs 
  b. Defined by IUPAC (International Union of Pure and Applied Chemistry)  
    - Standard Temperature and pressure as air at $0^oC$ (273.15 K, 32$^oF$) and $10^5$ pascals (1bar)* 

* The old IUPAC standard was 101.325 kPa, which was changed in 1932.  

  c. For ideal gas law 
    - STP is used as a reference point for the number of gas present (n) and the gas constant (R). 
    - Under STP condition: 22.4L/1 mole of any gas  
    - Molar volume**: $V_m = \frac{V}{n} = \frac{RT}{P} = \frac{8.3145J/(mole K) 273.15 K}{10^5 Pa} =  22.4 L/mol$  

** The molar volume of gas around STP can be calculated with sufficient accuracy using the ideal gas law. 

    

2. NTP (Normal Temperature and Pressure) 

a. NTP condition: 293.15 K at 1 atm 

  c. For ideal gas law 
    - Under NTP condition: 22.4L/1 mole of any gas  
    - Molar volume**: $V_m = \frac{V}{n} = \frac{RT}{P} = \frac{8.3145J/(mole K) 293.15 K}{101.325 kPa} =  24.04 L/mol$  

3. Summary 

	NTP	STP
Temperature	293.15 K	273.15 K
Pressure	1 atm (101.325 kPa)	0.987 atm (100 kPa = 1 bar)
Molar volume of the ideal gas	22.4 L/mol	24.04 ~ 24 L/mol