Difference between STP and NTP

Last Updated : 04 Feb, 2024

NTP and STP are two terms which are widely used in physics and chemistry to explain the various physical and chemical properties of liquids and gases. Let’s learn about these and their difference in detail.

What is STP?

STP, or standard temperature and pressure, is a commonly used set of conditions in chemistry to standardize measurements and compare different substances. It is defined as a temperature of 0 degrees Celsius (273.15 Kelvin) and a pressure of 1 atmosphere (101.325 kPa).

STP is used in many areas of chemistry, including thermodynamics, gas laws, and phase changes. For example, the ideal gas law, PV = nRT, uses STP as a reference point for the number of moles of gas present (n) and the gas constant (R). Under STP conditions, 1 mole of any gas occupies a volume of 22.4 litres. Similarly, the density of a substance is often reported at STP, as it allows for more accurate comparisons between different materials.

STP is also used in determining the standard enthalpy of formation, which is the amount of energy required to form one mole of a substance from its elements in their standard states. The standard state is defined as the substance being at a pressure of 1 atm and at its normal melting and boiling points.

It is important to note that many substances do not exist at STP and must be manipulated, such as through heating or cooling, to breach these conditions. Additionally, many real-world applications occur at different temperatures and pressures than STP, so it is crucial to consider these variables when interpreting and applying data.

In summary, STP is a widely used set of conditions in chemistry that serves as a reference point for measuring and comparing substances. It is defined as a temperature of 0 degrees Celsius and a pressure of 1 atmosphere. It is used in many areas of chemistry including thermodynamics, gas laws, phase changes and enthalpies.

Uses Of STP

STP (Standard Temperature and Pressure) is not commonly used in physics, as it is mostly used in chemistry as a reference point for measuring and comparing substances. However, it can be used in some areas of physics such as,

Fluid Mechanics

STP can be used as a reference point for the properties of gases and liquids, such as density, viscosity and vapour pressure. In fluid mechanics, STP (Standard Temperature and Pressure) is used as a reference point for the density and viscosity of fluids.

Thermodynamics

STP can be used as a reference state for thermodynamic properties such as internal energy, enthalpy and entropy. In thermodynamics, STP (Standard Temperature and Pressure) is used as a reference point for the properties of gases.

For example, when a gas is at STP, its specific volume (volume per unit mass) can be calculated using the ideal gas law, PV = nRT. The value of R, the specific gas constant, is also defined at STP.

Acoustics

The speed of sound in gases is dependent on temperature and pressure. STP can be used as a reference point for the speed of sound in the air. In acoustics, STP (Standard Temperature and Pressure) is used as a reference point for the speed of sound in gases. The speed of sound in a gas is dependent on the temperature and pressure of the gas, and it is used to calculate the wavelength and frequency of sound waves.

Astrophysics

STP is used as a reference point for measuring the properties of gases in space, such as density, temperature and pressure. In astrophysics, STP (Standard Temperature and Pressure) is not a commonly used reference point, as most astrophysical phenomena occur under conditions that are vastly different from STP. Instead, other reference points such as the Cosmic Microwave Background radiation (CMB) temperature, which is about 2.725 K, or the average density of the universe, which is about 10^-30 g/cm³, are used to understand the properties and behaviour of celestial objects and phenomena.

What is NTP?

NTP (Normal Temperature and Pressure) is a set of standard conditions used to define the physical properties of a substance, particularly in the field of thermodynamics. These standard conditions are typically set as a temperature of 20 degrees Celsius (68 degrees Fahrenheit) and a pressure of 1 atmosphere (101.325 kPa), which is roughly equivalent to the average temperature and pressure of the Earth’s atmosphere at sea level.

The use of NTP allows for the direct comparison of data from different experiments, as well as the prediction of the behaviour of a substance under different conditions. In thermodynamics, the properties of a substance are often described in terms of its internal energy, enthalpy, and entropy, and these properties can be measured at NTP to provide a baseline for comparison.

When measuring the properties of gases, the NTP conditions are often used to measure the volume of the gas at standard temperature and pressure (STP) which is defined as 0 degree Celsius and 1 atm.

It is important to note that NTP is standard, and not all experiments are conducted at NTP, but it is a way to have a common point of reference.

Uses Of NTP

NTP (Normal Temperature and Pressure) is used in physics for several purposes, including,

Calibration Of Instruments

In the calibration of instruments, NTP (Normal Temperature and Pressure) is commonly used as a reference point. NTP is defined as a temperature of 20 °C (293.15 K) and a pressure of 1 atm (101.325 kPa).

Calibration is the process of adjusting an instrument to ensure that it is measuring a physical quantity accurately and consistently. When an instrument is calibrated, it is typically compared to a known standard or reference, and any discrepancies are corrected.

Using NTP as a reference point allows for consistency in the calibration process. For example, a pressure gauge that is calibrated at NTP can be used to measure pressure at other temperatures and pressures, but the accuracy of the gauge will be known only at NTP.

Comparison of Data

In the comparison of data, NTP (Normal Temperature and Pressure) can be used as a reference point to ensure consistency and comparability of the data. NTP is defined as a temperature of 20 °C (293.15 K) and a pressure of 1 atm (101.325 kPa).

When collecting data, it is important to have a consistent set of conditions to ensure that the data is comparable. For example, when measuring the pressure of a gas, it is important to ensure that the temperature and pressure of the gas are the same for all measurements.

Prediction of Behavior

When predicting the behaviour of a system, it is important to have a consistent set of conditions to ensure that the predictions are comparable. For example, when predicting the pressure of a gas, it is important to ensure that the temperature and pressure of the gas are the same for all predictions.

Using NTP as a reference point allows for consistency in the prediction process. For example, if predictions are made at NTP, they can be compared to predictions made at other temperatures and pressures, but the accuracy of the predictions will be known only at NTP.

Thermodynamic Calculations

In thermodynamics, NTP (Normal Temperature and Pressure) is used as a reference point for thermodynamic calculations. NTP is defined as a temperature of 20 °C (293.15 K) and a pressure of 1 atm (101.325 kPa).

Thermodynamic calculations involve the calculation of properties such as internal energy, enthalpy, entropy, and Gibbs free energy. These properties are state functions, meaning they are dependent on the initial and final state of the system and not on the path taken to reach the state.

Using NTP as a reference point allows for consistency in the thermodynamic calculations. For example, if thermodynamic calculations are made at NTP, they can be compared to calculations made at other temperatures and pressures, but the accuracy of the calculations will be known only at NTP.