GENCHEM

• Enthalpy


  Like internal energy, the change in enthalpy is state function - measure of its condition
• Enthalpy


  H
• Enthalpy


  Heat flow in a system. Heat content
• Hess's Law


  Provides an indirect method of determining heat of reaction using a basis related chemical reaction with predetermined values of ∆Hf°
• Hess's Law of constant heat summation states that regardless of the multiple stages or steps in a reaction, the total enthalpy change for the reaction is the sum of all changes.
• Reverse reaction


  If we reverse the reaction, we have to reverse the sign in the change in enthalpy
• Enthalpy of the reaction is equal to the sum of the parts
• Rates of reaction


  Defined as the change in the concentration of reactants or products per change in time
• Factors that affect rates of reaction

  1. Temperature
  2. Concentration
  3. Surface area
• Temperature


  Higher temperature increases the kinetic energy in frequency of effective collisions between reactant molecules
• Concentration


  Higher concentration or pressure increases the number of reactant molecules in a given volume, leading to a more effective collision
• Surface area


  Larger surface area of solid reactants exposes more particles to collision other reactants
• Rate


  A quantity or amount considered in relation to or measured against another quantity or amount
• Order


  The arrangement or disposition of things in relation to each other according to a particular sequence, pattern, or method
• Law

  A rule defining correct procedure
• Reaction


  An action taken in response to something
• Order of a reactant


  The relationship between the rate and a particular concentration is illustrated by the reaction order with respect to a particular substance
• The rate of a reaction is expressed in molar per second (M/s)
• Zero-order reaction


  Has a constant rate that is equal to its rate constant regardless of changes in the concentration of the reactant.
• First-order reaction


  The rate doubles when the concentration of a reactant is doubled. A quadruple increase in reactant concentration means an increase of four times the original rate. In general, the rate increases in the same order as the concentration of the reactant
• Increasing the reactant concentration to twice as much quadruples as the original reaction rate. A triple increase in concentration means a ninefold increase in reaction rate


  Second-order reaction
• Overall reaction order


  Is the sum of the orders with respect to each reactant
• Weight loss shows the relationship between the rate of a chemical reaction and the concentration of its reactants


  For example, depletion of ozone layer, and chemical industry
• An integrated rate law relates to variables in a chemical reaction

  1. The concentration of the reactant
  2. The rate or time
• For zero-order reaction, the rate is independent of the concentration of the reactant. It remains constant throughout the course of the reaction and is equal to the rate constant
• The half-life of a reaction is the time it takes for an initial amount of reactant to be reduced to half
• The half-life of a zero-order reaction is directly proportional to the initial concentration of the reactant
• Chemical reaction


  A process in which one or more substance, the reactants, are converted to one or more different substances, the products.
• Reaction mechanism


  The sequence of elementary steps by which a chemical reaction occurs
• A reaction mechanism is a sequence of elementary reaction that describe the pathway from the reactants to the products
• Elementary reaction


  A single step in a reaction mechanism
• The overall reaction describes the reaction stoichiometry and is a summation of the elementary reaction.
• The sum of elementary steps must be equal to the overall balance equation
• An elementary reaction describes an individual molecular event
• Reaction intermediate 


  Is formed in one step and consumed in a subsequent step. They do not appear in the overall reaction
• The slow step in a reaction mechanism is called the rate determining steps or RDS
• Rate law expresses the relationship between the rate of a chemical reaction and the concentration of reactants
• Molecularity of the reaction


  A classification of an elementary reaction based on the number of molecules or atoms on the reactant side of the chemical reaction
• This molecularity isn't applicable to the overall reaction
• Unimolecular - 1

  Bimolecular - 2

  Termolecular - 3