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Standard Temperature and Pressure

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STP in Chemistry stands for Standard Temperature and Pressure it provides a standardized reference point for the measurement and comparison of physical and chemical properties of various substances, which is useful for scientists, engineers, and researchers in many fields. STP in Chemistry is the standard temperature and pressure condition that is used in various Thermodynamic conditions.

In this article, we will read about STP in Chemistry, STP of various Gases, Ideal Gas Equation at STP, and others in detail.

What is STP(Standard Temperature and Pressure)?

Standard Temperature and Pressure (STP) are reference conditions used to define the standard state of a substance. The standard temperature is defined as 0°C (273.15 K) and the standard pressure is defined as 100 kPa (1 atm). These conditions are used as reference points to make consistent and comparable measurements of the physical and chemical properties of substances.

For example, the density of a gas is commonly reported at STP. If a gas has a density of 1 g/L at STP, this means that at 0°C and 100 kPa, the gas has a mass of 1 gram per liter of volume. This allows scientists and engineers to compare the densities of different gases and make predictions about their behavior under different conditions.

Similarly, the standard molar volume of a gas is also defined at STP, which means the volume occupied by one mole of a gas at 0°C and 100 kPa. This information is useful for calculations involving gases and for predicting the behavior of gases under different conditions of temperature and pressure.

STP is defined by IUPAC as air at 0°C (273.15 K, 32°F) and 105 Pascal (1 Bar)

Need for Standard Temperature and Pressure(STP)

STP is an important concept used in Physics, Chemistry and other branches of sciences. It is used in various thermodynamic calculations. Various physical properties of the matter changes according to the change in temperature, and pressure. So having a standard temperature and pressure is must to perform various experiments and get the uniform results.

Standard Temperature and Pressure(STP) for Gases

STP value for the gases are most relevant as gases physical state of gas changes significantly with the change in temperature and pressure. The common definition of STP is a temperature of 273 K (0° Celsius or 32° Fahrenheit) and the standard pressure of 1 atm. All the thermodynamic calculation on a gas are achieved on the STP only, to get uniform result all across. STP effect of various gases are added in the article below,

Volume of Gases at STP

Any Gas irrespective of their atomic mass occupies 22.4 liters of volume. This value is constant for all the gases at STP and this law is called the Avogadro’s Law. In other words we can say that molar volume of gas at STP is 22.4 L. The volume of gas at STP is found with the relation PV = nRT.

Ideal Gas Equation at STP

The relation between volume pressure, and temperature of the gas particles is given using the Ideal Gas Equation and Ideal Gas Equation at Standard Temperature and Pressure (STP) is added below,

PV = nRT

where,

  • P is the Pressure of Gas at STP
  • V is the Volume of Gas at STP
  • T is the Temperature of Gas at STP
  • n is the Number of Moles of Gas at STP
  • R is the Universal Gas Constant

At standard temperature and pressure, the ideal gas equation can be expressed as PV = nRT.

This equation can be used to predict the behavior of a gas at different temperatures and pressures, as long as the gas is assumed to be ideal.

Properties of Water at STP(Standard Temperature and Pressure)

The most unique property of water at STP is, density of pure water (H2O) is 62.4 pounds per cubic foot (lb/ft3).

Examples of STP in Calculations

Here we discussed some examples of how STP is used in calculations,

Density of a Gas

The density of a gas at STP is calculated using the ideal gas law (PV = nRT). At STP, the pressure is 1 atm and the temperature is 0 degrees Celsius (273.15 Kelvin). Using these values, the density of a gas can be calculated by dividing the molar mass of the gas by the molar volume (V) at STP.

Density = Molar Mass / Molar Volume at STP

Molar Volume of an Ideal Gas

The molar volume of an ideal gas at STP can be calculated using the ideal gas law (PV = nRT) where P is the pressure, V is the molar volume, n is the number of moles, R is the ideal gas constant and T is the temperature.

V = nRT/P

Standard Enthalpy Change

The standard enthalpy change (ΔH°) is the change in enthalpy that occurs when a substance is transformed under standard conditions. For example, the standard enthalpy of combustion for a hydrocarbon can be determined by burning a known amount of the substance at STP and measuring the heat released.

ΔH° = q / n

where,

  • q is the Heat Released
  • n is the Number of Moles of Substance

Standard Temperature and Pressure (STP) Conditions

Standard Temperature and Pressure conditions that are used in all thermodynamics calculations are,

  • Standard Temperature is 273.15 K = 0°C = 32°F. This temperature is same as freezing point of water.
  • Standard Pressure is 1 atm = 760 Torr = 760 mm Hg = 101.35 kPa. This is standard pressure at sea level.
  • 1 mol of any gas contains 22.4 liters of Gas.

Difference between STP and NTP in Chemistry

Difference between STP and NTP can be understood with help of the table given below,

 Parameters Standard Temperature and Pressure (STP) Normal Temperature and Pressure (NTP)
Definition STP is a defined standard for temperature and pressure used in chemical and physical experiments. NTP represents typical atmospheric conditions found at sea level.
Temperature Temperature in the STP condition is 0°C (273.15 K) Temperature in the NTP condition is 20°C (293.15 K)
Pressure Pressure in the STP condition is 100 kPa (1 atm) Pressure in the STP condition is 101.325 kPa (1 atm)

Read More,

Solved Examples on STP in Chemistry

Example 1: Calculate the number of moles of a gas present in a 2 L container at a pressure of 1 atm and a temperature of 20 degrees Celsius.

Solution: 

Using Ideal Gas Law (PV = nRT)

Given,

  • P = 1 atm = 101,325 Pa
  • V = 2 L
  • T = 20 degrees Celsius = 293.15 Kelvin
  • R = 8.314 J/mol.K

n = PV / RT

n = (101,325 Pa × 2 L) / (8.314 J/mol-K × 293.15 K)

n = 0.68 mol

Example 2: Given the heat released during the combustion of a hydrocarbon as -4000 J, calculate the standard enthalpy change of combustion per mole of hydrocarbon.

Solution:

Standard Enthalpy Change (ΔH°) = q / n

Given,

  • q = -4000 J
  • n = 1 mole

ΔH° = -4000 J / 1 mole = -4000 J/mol

So the standard enthalpy change of combustion per mole of hydrocarbon is -4000 J/mol.

Example 3: A sample of gas has a volume of 2.5 L at STP. What is the number of moles of gas present in the sample.

Solution:

Using Ideal Gas Equation PV = nRT

n = (PV) / (RT) 

n = (100 kPa × 2.5 L) / (8.31 J/mol-K × 273.15 K) 

n = 0.0292 moles

Example 4: A sample of gas has a volume of 10.0 L at a pressure of 200 kPa and a temperature of 300 K. What is the number of moles of gas present in the sample?

Solution:

Using Ideal Gas Equation PV = nRT

n = (PV) / (RT)

n = (200 kPa × 10.0 L) / (8.31 J/molK × 300 K) 

n = 0.69 moles

FAQs on STP(Standard Temperature and Pressure)

1. What is STP in Chemistry?

STP in chemistry is the standard, temperature and pressure at which all the thermodynamic calculation are made. The STP in chemistry is 0°C (273.15 K) and 1 atm pressure.

2. What is Difference between STP and NTP?

STP is defined as a standard temperature of 0°C (273.15 K) and a standard pressure of 100 kPa (1 atm). NTP is defined as a normal temperature of 20°C ( 293.15 K) and a normal pressure of 101.325 kPa (1 atm).

3. Can Ideal Gas Equation be Used at Conditions other than STP?

Yes, the ideal gas equation can be used at conditions other than STP, but the results may not be as accurate as they would be at STP.

4. How can Ideal Gas Equation be used to Predict Behavior of a Gas?

The ideal gas equation can be used to predict the behavior of a gas by considering the pressure, volume, temperature, number of moles, and the ideal gas are constant.

5. How do you Find the Standard Temperature and Pressure?

Standard Temperature and Pressure is calculated using the Ideal Gas Equation as, PV = nRT

6. Is the Volume for All Gases the Same at STP?

Yes, the volume of all the gases is same at STP and this is called the Avogadro’s Law. And the molar volume of gas at STP is 22.4 liters.

7. What is STP equal to?

STP (Standard Temperature Pressure) is equal to 0 degree Celsius and 1 atm.

8. Is STP 25 or 0?

STP is 0°C or 273.15 Kelvin not 25°C.



Last Updated : 18 Nov, 2023
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