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Chemical kinetics, also known as reaction kinetics, is the branch of physical chemistry that is concerned with understanding the rates of chemical reactions. It is different from chemical thermodynamics, which deals with the direction in which a reaction occurs but in itself tells nothing about its rate.
A molecular vibration is a periodic motion of the atoms of a molecule relative to each other, such that the center of mass of the molecule remains unchanged. The typical vibrational frequencies range from less than 10 13 Hz to approximately 10 14 Hz, corresponding to wavenumbers of approximately 300 to 3000 cm −1 and wavelengths of approximately 30 to 3 μm.
In physics and chemistry, a molecule (or other group of atoms) can undergo libration if it is subject to external forces or constraints that restrict its orientation. For example, in liquid water , any given water molecule is attracted to neighboring molecules, so that it has a preferred orientation and cannot freely rotate.
There are two main descriptions of motion: dynamics and kinematics.Dynamics is general, since the momenta, forces and energy of the particles are taken into account. In this instance, sometimes the term dynamics refers to the differential equations that the system satisfies (e.g., Newton's second law or Euler–Lagrange equations), and sometimes to the solutions to those equations.
These equations represent the simple harmonic motion of the pendulum with an added coupling factor of the spring. [1] This behavior is also seen in certain molecules (such as CO 2 and H 2 O), wherein two of the atoms will vibrate around a central one in a similar manner. [1]
The solution of these equations of motion provides a description of the position, the motion and the acceleration of the individual components of the system, and overall the system itself, as a function of time. The formulation and solution of rigid body dynamics is an important tool in the computer simulation of mechanical systems.
With cylindrical co-ordinates which are described as î and j, the motion is best described in polar form with components that resemble polar vectors.As with planar motion, the velocity is always tangential to the curve, but in this form acceleration consist of different intermediate components that can now run along the radius and its normal vector.
The general equation can then be written as [6] = + + (),. where the "force" term corresponds to the forces exerted on the particles by an external influence (not by the particles themselves), the "diff" term represents the diffusion of particles, and "coll" is the collision term – accounting for the forces acting between particles in collisions.