Basic formulas of molecular physics

Molecular physics is an extensive branch of physics that studies the structure of matter at the molecular level, changes in the macroparameters of the system under the influence of the external environment, and phase transitions. The properties of polymers and plasmas are also investigated by molecular physics. Formulas and definitions of this section, which will be useful in solving problems, are given in this article.

Basic concepts of the section

A molecule is the smallest unit of a substance possessing all its properties.

The ideal gas is a gas for which the intermolecular interaction force is zero, the molecules are treated as material points, and the impacts between them are absolutely elastic. Many formulas of molecular physics are applied precisely with respect to an ideal gas.

Energy is a quantity that characterizes the ability of a system to perform work.

Work - the amount of energy transferred to the system through changing its parameters.

Other concepts of this section: temperature, internal energy, potential energy, diffusion, thermal conductivity, amount of matter, heat capacity, evaporation, condensation, crystallization, saturated vapor.

Basic Formulas

The formulas of molecular physics establish a connection between different parameters of the system. The basic formulas of this section include the Clapeyron equation describing the state of an ideal gas, the laws of Boyle, Charles, and Gay-Lussac.

The Clapeyron equation is written as:

PV = nRT

Here p is the pressure, n is the amount of matter in moles, R is the universal gas constant, T is the temperature in kelvins, and V is the volume occupied by the gas.

From this formula of molecular physics with the help of simple transformations other laws of state are obtained:

PV = const (the formulation of the Boyle-Mariotte law, which is applied to the isothermal process);

V / T = const (the first Gay-Lussac law that applies to the isobaric process);

P / T = const (Charles's law applies to the isochoric process).

Other important formulas of molecular physics:

N = m / M = N / Na (formula for finding the amount of substance).

P = nkT.

In the last formula, n is the concentration, k is the constant, and the Boltzmann constant.

E = (3NkT) / 2 (the formula for finding the thermal energy).

P = p ₁ + p ₂ + ... + p _i (formula for determining the pressure of a gas mixture, known as the Dalton law).

Formulas of thermodynamics and statistical physics

Statistical physics is also a branch of molecular physics. Some formulas of molecular physics used in statistical physics and thermodynamics are given above.

Q = mc (t ₂ -t ₁ )

Q = A + (U2-U ₁ ) (U _i is the internal energy)

DH = TdS + Vdp

Here, H is the enthalpy.

G is the Gibbs energy, or the thermodynamic potential.

V = dG / dp

S = -dG / dT (S is the entropy, the value introduced by Clausius, the probability measure).