chemical reaction

Examples of chemical reaction in the following topics:

• Energy Changes in Chemical Reactions

  • Due to the absorption of energy when chemical bonds are broken, and the release of energy when chemical bonds are formed, chemical reactions almost always involve a change in energy between products and reactants.
  • By the Law of Conservation of Energy, however, we know that the total energy of a system must remain unchanged, and that oftentimes a chemical reaction will absorb or release energy in the form of heat, light, or both.
  • The energy change in a chemical reaction is due to the difference in the amounts of stored chemical energy between the products and the reactants.
  • This stored chemical energy, or heat content, of the system is known as its enthalpy.
  • Describe the types of energy changes that can occur in chemical reactions

• Introduction to Chemical Reactivity

  • Now that we can recognize these actors ( compounds ), we turn to the roles they are inclined to play in the scientific drama staged by the multitude of chemical reactions that define organic chemistry.
  • Chemical Reaction: A transformation resulting in a change of composition, constitution and/or configuration of a compound (referred to as the reactant or substrate).
  • Reactant or Substrate: The organic compound undergoing change in a chemical reaction.
  • Reagent: A common partner of the reactant in many chemical reactions.
  • Catalysts are substances that accelerate the rate ( velocity ) of a chemical reaction without themselves being consumed or appearing as part of the reaction product.

• Amount of Reactants and Products

  • Stoichiometry is the study of the relative quantities of reactants and products in chemical reactions and how to calculate those quantities.
  • Chemical equations are symbolic representations of chemical reactions.
  • The numerical coefficients next to each chemical entity denote the proportion of that chemical entity before and after the reaction.
  • The law of conservation of mass dictates that the quantity of each element must remain unchanged in a chemical reaction.
  • Reaction stoichiometry describes the quantitative relationship among substances as they participate in various chemical reactions.

• Changes in Temperature

  • Changes in temperature shift the equilibrium state of chemical reactions; these changes can be predicted using Le Chatelier's Principle.
  • Changes in temperature can affect the equilibrium state of a reversible chemical reaction.
  • Le Chatelier's Principle states that when changes are made to a reversible chemical reaction in equilibrium, the system will compensate for that change with a predictable, opposing shift.
  • Reactions can be classified by their enthalpies of reaction.
  • Evaluate the effect of temperature on the equilibrium state of a chemical reaction

• Chemical Kinetics and Chemical Equilibrium

  • Chemical kinetics is the study of how quickly a chemical reaction occurs and what factors affect its rate.
  • Obviously, there are factors that affect the rates of chemical reactions.
  • Knowing how quickly a chemical reaction occurs is a crucial factor in how the reaction affects its surroundings and vice versa.
  • The interval required for a chemical change or reaction to occur is called the reaction time.
  • Discuss which aspects of a reaction are described by chemical kinetics

• Writing Chemical Equations

  • A chemical equation expresses a chemical reaction by showing how certain reactants yield certain products.
  • A chemical equation is the symbolic representation of a chemical reaction.
  • The reactants (the starting substances) are written on the left, and the products (the substances found in the chemical reaction) are written on the right.
  • The coefficients next to the symbols of entities indicate the number of moles of a substance produced or used in the chemical reaction.
  • A chemical equation consists of the chemical formulas of the reactants (on the left) and the products (on the right).

• 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

• The Rate Law

  • The rate law for a chemical reaction relates the reaction rate with the concentrations or partial pressures of the reactants.
  • The rate law for a chemical reaction is an equation that relates the reaction rate with the concentrations or partial pressures of the reactants.
  • The exponents x and y vary for each reaction, and they must be determined experimentally; they are not related to the stoichiometric coefficients of the chemical equation.
  • To reiterate, the exponents x and y are not derived from the balanced chemical equation, and the rate law of a reaction must be determined experimentally.
  • What is the reaction order?

• Change in Enthalpy

  • Enthalpy changes are associated with chemical processes, and are important in understanding how the reaction has changed a chemical system.
  • Any time a thermodynamic system undergoes a transformation or a chemical reaction, there is an energy (enthalpy) change associated with the process.
  • Any chemical reaction can be characterized by a change in enthalpy, denoted as: $\Delta H = \Delta H_{final} - \Delta H_{initial}$
  • This lesson introduces Enthalpy and the energy of chemical bonding.
  • We discuss where the energy in chemical bonds comes from in terms of internal energy and enthalpy, as well as how to approximate the overall heat of reaction using bond enthalpies.

• Physical and Chemical Changes to Matter

  • As the names suggest, a physical change affects a substance's physical properties, and a chemical change affects its chemical properties.
  • Chemical changes are also known as chemical reactions.
  • The "ingredients" of a reaction are called the reactants, and the end results are called the products.
  • For example, the color of the element chromium is determined by its oxidation state; a single chromium compound will only change color if it undergoes an oxidation or reduction reaction.
  • The best way to be completely certain whether a change is physical or chemical is to perform chemical analyses, such as mass spectroscopy, on the substance to determine its composition before and after a reaction.