# Question af461

Jul 21, 2015

They are a set of conditions for pressure and temperature.

#### Explanation:

I assume that you want to know the difference between STP and NTP.

Both STP and NTP are a set of conditions that establish working temperature and pressure.

STP, or Standard Temperature and Pressure, conditions correspond to a temperature of ${0}^{\circ} \text{C}$, or 273.15 K, and a pressure of 100 kPa.

NTP, or Normal Temperature and Pressure, conditions correspond to a temperature of ${20}^{\circ} \text{C}$, or 293.15 K, and a pressure of 1 atm.

A pressure of 1 atm is equivalent to 101.325 kPa.

This means that these two sets of conditions differ by

• Temperature - STP is ${0}^{\circ} \text{C}$ and NTP is ${20}^{\circ} \text{C}$
• Pressure - STP is 100 kPa and NTP is 101.325 kPa

When it comes to idel gases, these two conditions also differ in the volume occupies by 1 mole of gas - this is called the molar volume of a gas.

To show why that is, use the ideal gas law equation

• At STP conditions

$P V = n R T \implies \frac{V}{n} = \frac{R T}{P}$

V/n = (0.082 (cancel("atm") * "L")/("mol" * cancel("K")) * (273.15 + 0)cancel("K"))/(100/101.325cancel("atm")) = color(green)("22.7 L/mol")

This tells you that 1 mole of any ideal gas will occupy exactly

1cancel("mole") * "22.7 L"/cancel("mol") = "22.7 L"

• At NTP conditions

V/n = (0.082 (cancel("atm") * "L")/("mol" * cancel("K")) * (273.15 + 20)cancel("K"))/(101.325/101.325cancel("atm")) = color(green)("24.0 L/mol")

This time, 1 mole of any ideal gas will occupy

1cancel("mole") * "24.0 L"/cancel("mol") = "24.0 L"#