reaction

Examples of reaction in the following topics:

• Reaction Quotients

  • The reaction quotient is a measure of the relative amounts of reactants and products during a chemical reaction at a given point in time.
  • The reaction quotient, Q, is a measure of the relative amounts of reactants and products during a chemical reaction at a given point in time.
  • By comparing the value of Q to the equilibrium constant, Keq, for the reaction, we can determine whether the forward reaction or reverse reaction will be favored.
  • As the reaction proceeds, assuming that there is no energy barrier, the species' concentrations, and hence the reaction quotient, change.
  • Calculate the reaction quotient, Q, and use it to predict whether a reaction will proceed in the forward or reverse direction

• Changes in Temperature

  • Changes in temperature can affect the equilibrium state of a reversible chemical reaction.
  • Reactions can be classified by their enthalpies of reaction.
  • A diagram of the reaction coordinate for an exothermic reaction is shown in .
  • Exothermic reactions will be shifted toward the reactants.
  • Endothermic reactions, on the other hand, will be shifted towards product formation as heat is removed from the reaction's surrounding environment.

• Ene Reactions

  • The reverse process is called a retro ene reaction.
  • This is the same bond bookkeeping change exhibited by electrocyclic reactions, but no rings are formed or broken in an ene reaction unless it is intramolecular.
  • The following examples illustrate some typical ene reactions, with equation 3 being an intramolecular ene reaction.
  • Reaction 4 is drawn as a retro ene reaction, although this has not been demonstrated to be general for all reactions of allylic alcohols with thionyl chloride.
  • A similar acid-catalyzed reaction of simple aldehydes with alkenes to give allylic alcohols, 1,3-diols or 1,3-dioxanes is known as the Prins reaction.

• Energy Changes in Chemical Reactions

  • For example, combustion reactions are usually exothermic.
  • In exothermic reactions, the products have less enthalpy than the reactants, and as a result, an exothermic reaction is said to have a negative enthalpy of reaction.
  • For example, decomposition reactions are usually endothermic.
  • Thus, an endothermic reaction is said to have a positive enthalpy of reaction.
  • Significant heat energy is needed for this reaction to proceed, so the reaction is endothermic.

• Non-Ionic Reactions

  • With few exceptions, the multitude of reactions discussed in this and other introductory texts are classified as ionic reactions.
  • Here we shall consider two other classes of organic reactions: Free-Radical Reactions & Pericyclic Reactions.
  • One type of "free-radical reaction", alkane halogenation has already been described.
  • In contrast to ionic reactions, both free radical and pericyclic reactions may occur in the gas phase, as well as in solution in various solvents.
  • Also, these nonionic reactions are more tolerant of spectator functional groups than are many ionic reactions.

• Substitution Reactions of Benzene and Other Aromatic Compounds

  • The chemical reactivity of benzene contrasts with that of the alkenes in that substitution reactions occur in preference to addition reactions, as illustrated in the following diagram (some comparable reactions of cyclohexene are shown in the green box).
  • Many other substitution reactions of benzene have been observed, the five most useful are listed below (chlorination and bromination are the most common halogenation reactions).
  • Since the reagents and conditions employed in these reactions are electrophilic, these reactions are commonly referred to as Electrophilic Aromatic Substitution.
  • The specific electrophile believed to function in each type of reaction is listed in the right hand column.

• Metal Exchange Reactions

  • Alternative methods of preparing a wide variety of organometallic compounds generally involve an exchange reaction in which a given metal is either moved to a new location or replaced by a new metal, which may include B, Al, Ti, V, Fe, Ni, Cu, Mo, Ru, Pd, Sn, Pt, Hg & Pb.

• Exothermic and Endothermic Processes

  • Endothermic reactions absorb energy from the environment, while exothermic reactions release energy to the environment.
  • Exothermic reactions are reactions or processes that release energy, usually in the form of heat or light.
  • Endothermic reactions are reactions that require external energy, usually in the form of heat, for the reaction to proceed.
  • As such, the change in enthalpy for an endothermic reaction is always positive.
  • In an endothermic reaction, the products are higher in energy than the reactants.

• The Rate Law

  • The rate law for a chemical reaction relates the reaction rate with the concentrations or partial pressures of the reactants.
  • For the general reaction$aA + bB \rightarrow C$ with no intermediate steps in its reaction mechanism, meaning that it is an elementary reaction, the rate law is given by:
  • A smaller rate constant indicates a slower reaction, while a larger rate constant indicates a faster reaction.
  • What is the reaction order?
  • A variety of reaction orders are observed.

• By Reaction Type