kinetic energy

Examples of kinetic energy in the following topics:

• Distribution of Molecular Speeds and Collision Frequency

  • Depending on the nature of the particles' relative kinetic energies, a collision causes a transfer of kinetic energy as well as a change in direction.
  • Kinetic energy can be distributed only in discrete amounts known as quanta, so we can assume that any one time, each gaseous particle has a certain amount of quanta of kinetic energy.
  • Although higher velocity states are favored statistically, however, lower energy states are more likely to be occupied because of the limited kinetic energy available to a particle; a collision may result in a particle with greater kinetic energy, so it must also result in a particle with less kinetic energy than before.
  • As the temperature increases, the particles acquire more kinetic energy.
  • Larger molecular weights narrow the velocity distribution because all particles have the same kinetic energy at the same temperature.

• Kinetic Molecular Theory and Gas Laws

  • The collisions exhibited by gas particles are completely elastic; when two molecules collide, total kinetic energy is conserved.
  • The average kinetic energy of gas molecules is directly proportional to absolute temperature only; this implies that all molecular motion ceases if the temperature is reduced to absolute zero.
  • According to Kinetic Molecular Theory, an increase in temperature will increase the average kinetic energy of the molecules.
  • Increasing the kinetic energy of the particles will increase the pressure of the gas.
  • Reviews kinetic energy and phases of matter, and explains the kinetic-molecular theory of gases.

• Solid Solubility and Temperature

  • As the temperature of a solution is increased, the average kinetic energy of the molecules that make up the solution also increases.
  • This increase in kinetic energy allows the solvent molecules to more effectively break apart the solute molecules that are held together by intermolecular attractions.
  • The average kinetic energy of the solute molecules also increases with temperature, and it destabilizes the solid state.
  • The increased vibration (kinetic energy) of the solute molecules causes them to be less able to hold together, and thus they dissolve more readily.

• The Photoelectric Effect

  • If excess photon energy is absorbed, some of the energy liberates the electron from the atom and the rest contributes to the electron's kinetic energy as a free particle.
  • However, if just the intensity of the incident radiation is increased, there is no effect on the kinetic energies of the photoelectrons.
  • The maximum kinetic energy of an ejected electron is given by
  • The maximum kinetic energy of an ejected electron is then
  • Kinetic energy must be positive for ejection to take place, so we must have f > f0 for the photoelectric effect to occur.

• The Arrhenius Equation

  • If you recall that RT is the average kinetic energy, it will be apparent that the exponent is just the ratio of the activation energy, Ea, to the average kinetic energy.
  • This affords a simple way of determining the activation energy from values of k observed at different temperatures.
  • Recall that the exponential part of the Arrhenius equation ($e^{\frac{-E_a}{RT}}$) expresses the fraction of reactant molecules that possess enough kinetic energy to react, as governed by the Maxwell-Boltzmann distribution.
  • Depending on the magnitudes of Ea and the temperature, this fraction can range from zero, where no molecules have enough energy to react, to unity, where all molecules have enough energy to react.
  • This could only occur if either the activation energy were zero, or if the kinetic energy of all molecules exceeded Ea—both of which are highly unlikely scenarios.

• Reaction Energetics

  • At room temperature, indeed at any temperature above absolute zero, the molecules of a compound have a total energy that is a combination of translational (kinetic) energy, internal vibrational and rotational energies, as well as electronic and nuclear energies.
  • The temperature of a system is a measure of the average kinetic energy of all the atoms and molecules present in the system.
  • As shown in the following diagram, the average kinetic energy increases and the distribution of energies broadens as the temperature is raised from T1 to T2.
  • Since reacting molecules must collide to interact, and the necessary activation energy must come from the kinetic energy of the colliding molecules, the first two factors are obvious.
  • The sum n + m is termed the kinetic order of a reaction.

• Comparison of Enthalpy to Internal Energy

  • Internal energy and enthalpy are both measurements that quantify the amount of energy present in a thermodynamic system.
  • It includes the energy needed to create the system, but excludes the energy needed to displace the system's surrounding or energy displacement due to external forces.
  • Internal energy encompasses both potential and kinetic energy.
  • Because the internal energy encompasses only the energy contained within a thermodynamic system, the internal energy of isolated systems cannot change.
  • Sometimes, measuring the internal energy of a system may be an inaccurate gauge of the change in energy.

• The Kinetic Molecular Theory of Matter

  • The kinetic molecular theory of matter explains how matter can change among the phases of solid, liquid, and gas.
  • All particles have energy, but the energy varies depending on the temperature the sample of matter is in.
  • Molecules in the solid phase have the least amount of energy, while gas particles have the greatest amount of energy.
  • The temperature of a substance is a measure of the average kinetic energy of the particles.
  • The kinetic theory of matter is also illustrated by the process of diffusion.

• Nuclear Binding Energy and Mass Defect

  • The binding energy of nuclei is always a positive number, since all nuclei require net energy to separate them into individual protons and neutrons.
  • Once mass defect is known, nuclear binding energy can be calculated by converting that mass to energy by using E=mc2.
  • This energy—available as nuclear energy—can be used to produce nuclear power or build nuclear weapons.
  • When a large nucleus splits into pieces, excess energy is emitted as photons, or gamma rays, and as kinetic energy, as a number of different particles are ejected.
  • For elements lighter than iron-56, fusion will release energy because the nuclear binding energy increases with increasing mass.

• Reaction Rates and Kinetics

  • Useful information about reaction mechanisms may be obtained by studying the manner in which the rate of a reaction changes as the concentrations of the reactant and reagents are varied.This field of study is called kinetics.
  • Nevertheless, evidence for their existence may be obtained by other means, including spectroscopic observation or inference from kinetic results.
  • The potential energy of a reacting system changes as the reaction progresses.The overall change may be exothermic ( energy is released ) or endothermic ( energy must be added ), and there is usually an activation energy requirement as well.
  • Tables of Standard Bond Energies are widely used by chemists for estimating the energy change in a proposed reaction.