What is the Difference Between Universal Gas Constant and Characteristic Gas Constant

The main difference between universal gas constant and characteristic gas constant is that the universal gas constant (R) is a fundamental physical constant applicable to any ideal gas, whereas the characteristic gas constant is specific to a particular gas and is often denoted by R with a subscript indicating the gas.

The universal gas constant and characteristic gas constant are fundamental concepts in thermodynamics and gas laws. While the universal gas constant, denoted as R, applies to all gases and is a constant value, the characteristic gas constant, often represented by the specific gas symbol R for a particular substance, is unique to individual gases.

Key Areas Covered

1. What is an Universal Gas Constant 
      – Definition, Features, Use
2. What is a Characteristic Gas Constant
      – Definition, Features, Use 
3. Similarities Between Universal Gas Constant and Characteristic Gas Constant
      – Outline of Common Features
4. Difference Between Universal Gas Constant and Characteristic Gas Constant
      – Comparison of Key Differences
5. FAQ: Universal Gas Constant and Characteristic Gas Constant
      – Frequently Asked Questions

Key Terms

Universal Gas Constant, Characteristic Gas Constant

What is Universal Gas Constant

The universal gas constant, often denoted as R, is a fundamental physical constant that plays a crucial role in the field of thermodynamics and the study of gases. With a value of approximately 8.314 joules per mole-kelvin (J/(mol·K)), the universal gas constant connects the microscopic world of individual gas particles to macroscopic thermodynamic properties.

Originally formulated in the ideal gas law, which states that the product of pressure and volume divided by temperature is a constant for any ideal gas, the universal gas constant is a bridge between observable quantities and the underlying behavior of gas molecules. This law is expressed mathematically as PV = nRT. Here, P is the pressure, V is the volume, n is the number of moles, R is the universal gas constant, and T is the temperature in kelvin.

One of the critical aspects of the universal gas constant is its units. The unit of R depends on the units used for pressure, volume, and temperature. In the International System of Units (SI), the common unit for pressure is the pascal (Pa), for volume, it is the cubic meter (m³), and for temperature, it is the kelvin (K). Therefore, the SI unit for the universal gas constant is joules per mole-kelvin (J/(mol·K)).

The value of the universal gas constant originates from various measurements and experiments involving gases. The most common method involves measuring the heat capacity of gases at constant volume or constant pressure. Moreover, one can express the relationship between heat capacity (C), the number of moles (n), and the change in temperature (ΔT) as ΔQ = nCΔT. By carefully conducting such experiments and analyzing the data, scientists have been able to determine the value of the gas constant with high precision.

Ideal Gas Law

It’s important to note that the ideal gas law is an approximation that holds true under certain conditions. Real gases deviate from ideal behavior at high pressures and low temperatures, where intermolecular forces become significant. However, the universal gas constant remains a valuable tool even when dealing with non-ideal gases, as it can be used in modified forms of the ideal gas law that account for deviations.

Applications of Universal Gas Constant

The universal gas constant also finds application in various scientific disciplines beyond chemistry. In physics, it is used in equations related to kinetic theory, where the behavior of gases is described in terms of the motion of individual particles. In engineering, the gas constant is frequently useful in thermodynamic calculations, particularly in the design and analysis of heat exchangers, engines, and other systems involving gases.

What is Characteristic Gas Constant

The characteristic gas constant is specific to a particular gas and is often denoted by R, with a subscript indicating the gas. It is valid for normal gases as the normal gases are not ideal. It could be calculated in the following way.

R_specific  =  R/M,

where R_specific   –  Characteristic gas constant

  R   – Universal gas constant

  M  –  Molar mass of the gas

One can apply characteristic gas constant for a mixture of gasses as well. Then, the R should be divided by the molar mass of the mixture of gases. This characteristic gas constant is also called a specific gas constant because its value depends on the considered gas or the mixture of gases.

Similarities Between Universal Gas Constant and Characteristic Gas Constant

• Both represent the ideal gas law and are useful in thermodynamics equations.
• Both constants have units derived from the International System of Units (SI), such as Joules per mole per Kelvin (J/mol·K) for R.
• They are useful in gas laws, such as the ideal gas law, to relate the properties of gases under varying conditions.

Difference Between Universal Gas Constant and Characteristic Gas Constant

Definition

The universal gas constant (R) is a constant used in the ideal gas law and has the same value for all gases, approximately 8.314 J/(mol·K). On the other hand, the characteristic gas constant (R_specific) is specific to a particular gas and is obtained by dividing the universal gas constant by the molar mass of the gas.

Applications

While the universal gas constant is applicable to all gases, the characteristic gas constant is specific to a particular gas.

Value

The universal gas constant has a constant value of approximately 8.314 J/(mol·K), while the characteristic gas constant varies depending on the molar mass of the specific gas.

FAQ: Universal Gas Constant and Characteristic Gas Constant

Is the ideal gas constant and universal gas constant the same?

Yes, the ideal gas constant and universal gas constant are the same.

To which gases is the universal gas constant applied?

Universal gas constant is applicable to ideal gases.

What is the value of the universal gas constant?

The universal gas constant has a value of 8.314 J/(mol·K).

Conclusion

The main difference between universal gas constant and characteristic gas constant is that the universal gas constant (R) is a fundamental physical constant applicable to any ideal gas, whereas the characteristic gas constant is specific to a particular gas and is often denoted by R with a subscript indicating the gas.

Reference:

1. “Gas Content.” Byju’s.
2. “Gas constant.” Wikipedia. Wikipedia Foundation.

Image Courtesy:

1. “Ideal gas law relationships” By Cmglee – Own work (CC BY-SA 4.0) via Commons Wikimedia