Before looking for the meaning of the phrase "gas law", it is necessary to find out what gas is. Gases are substances whose particles move randomly in space. These substances are characterized by very weak intermolecular, interatomic and interionic interactions. A gas is also called a gaseous state, that is, one of four, in addition to the liquid, solid and plasma, aggregate states of a substance. Gases have their own laws. What is gas law?
Definition
From a physical point of view, gas laws are laws that explain isoprocesses that occur in an ideal gas. An interesting fact is that in chemistry there are also certain laws for the description of such substances that overlap with the laws of physics. However, these laws apply to real gases. Now it’s worth figuring out what an ideal gas and isoprocess are. Let's get started.
Perfect gas
An ideal gas is a mathematical model of a real gas, in which the assumption is made that there is completely no interaction between gas particles. From this assumption it follows that the particles are in contact only with the vessel in which the substance is located, and also that the mass of particles of this substance is so small that it can be completely excluded from consideration.
Isoprocesses
To answer the question of what isoprocess is, it is necessary to turn to thermodynamics (one of the branches of physics). To describe the state of the gas (ideal gas), the main parameters are pressure, temperature and volume.
So, isoprocesses are processes occurring in gases, provided that one of these three parameters remains unchanged over time. In isothermal processes the temperature does not change, in isobaric - pressure, and in isochoric - volume.
Mendeleev-Clapeyron equation
Before discussing gas laws, it is necessary to find out what the Mendeleev-Clapeyron equation is and what relation this equation has to gases and their laws. To describe the dependence of all the same indicators on each other - pressure, volume, temperature, the universal gas constant and volume (molar) are also added.
The equation has the following notation: pV = R * T.
R is the universal gas constant, it can be calculated independently, or you can use the already known value - 8.3144598 (48) J ⁄ (mol ∙ K).
So, molar volume is the ratio of volume to the amount of substance (in moles), and the amount of substance, in turn, is the ratio of mass to molar mass.
The equation can be written as follows: pV = (m / M) * R * T.
What are the laws of gases in physics?
As mentioned earlier, in physics, isoprocesses are considered. There are formulas for the dependence of three basic quantities (volume, pressure, temperature) on each other. Gas laws in physics:
- The Boyle-Marriott law, applied in the case of an isothermal process: the product of pressure on the volume of gas remains unchanged over time. Based on the Mendeleev-Clapeyron equation - pV = (m / M) * R * T = const, this law states that the result of multiplying the pressure and volume will be constant, provided that the gas temperature and its mass are unchanged.
- The Gay-Lussac Law, which applies to isobaric processes. In this case, the ratio of volume and temperature remains unchanged: V / T = const. The Gay-Lussac law can be formulated as follows: if the pressure and mass of the gas remain constant over time, then the quotient of dividing the volume by temperature is a constant.
- Charles's law is for isochoric processes. The ratio of pressure and temperature does not undergo changes: p / T = const. In this case, the ratio of gas pressure and temperature is constant with constant pressure and mass.
Gas laws: chemistry
Among these laws:
- Avogadro's Law. It is formulated as follows: equal volumes of different gases contain the same number of molecules, ceteris paribus (pressure and temperature). It follows from this law - under normal conditions (the pressure 101.235 kPa and temperature 273 K are called normal conditions) the volume of absolutely any gas occupied by 1 mole is 22.4 liters.
- Dalton's law: the volumes occupied by the gases that react with each other and the products obtained during the reaction, when dividing the former by the latter, result in small, but integer numbers, which are called coefficients.
- The law of partial pressures: in order to determine the pressure of a mixture of gases, it is necessary to add the pressures created by the gases of the mixture.
Variety of laws applicable to gases
Perhaps many people think that gases are the simplest state of aggregation: particles move randomly, and the distance between them is maximum (especially in comparison with solids), and the mass of these particles is small. However, the laws used to describe the states of such substances are very diverse. From the above it follows that not only physics is studying the issue of gas laws. Moreover, in physics and chemistry there are not one or two of them. From this we can come to the conclusion that it is not always that which seems simple, that is, in fact, also.