Chemistry - Prefinals

• The Rate of Chemical Reaction - mathematical representation that describes and visualizes the behavior of solutions in dynamic equilibrium
• Peter Waage & Cato Maximillian Guldberg (1864) - Norwegian chemists who developed chemical kinetics thru Law of Mass action
• Law of Mass Action

  • “The speed of chemical reaction is proportional to the quantity of the reacting substances” 
  • “The rate of chemical reaction is proportional to the product of the masses/concentrations of the reacting substances”
• Chemical Kinetics - study of the reaction mechanism and rates of chemical reactions
• Reaction Mechanism - the breaking of old bonds and formation of new bonds
• Activated Complex - temporary stage of breaking old bonds and formation of new bonds

  • Breaking of old bonds is shown as a broken line while the formation of new bonds is shown by small circles
• Factors Affecting the Rates of Chemical Reaction

  1. concentration of reacting substances
  2. pressure
  3. temperature
• Rate of a chemical reaction - product of the concentration of the reacting substances each concentration is raised to an exponent that is determined experimentally
• Collision Theory - explains that gas-phase chemical reactions occur when molecules collide with sufficient kinetic energy.

  • Based on the kinetic theory of gasses, so gas-phase chemical reactants are dealt with assuming ideal gas behavior is applied
• Collision Theory states that:

  1. All molecules are traveling through space in a straight line
  2. All molecules are rigid spheres
  3. The reactions concerned are between only two molecules
  4. The molecules need to collide
• Catalysts - substance that increases or decreases the rate of a chemical reaction without undergoing a permanent chemical change
• 2 types of catalysts

  1. Promotor or Positive Catalysts
  2. Inhibitor or Negative Catalysts
• Promoter or Positive Catalysts - substances that increases the rate of chemical reaction as it decreases the activation energy
• Inhibitor or Negative Catalysts - substances that decreases the rate of chemical reaction as it increases the activation energy
• Chemical Thermodynamics

  • Study of the interrelation of heat and work with chemical reactions or with physical changes of state within the confines of thermodynamics
• Thermodynamics - deals with the relations between heat and other forms of energy
• Rudolf Julius Emmanuel Clausius - proposed that the heat evolved in a combustion reaction (thermochemistry)
• Josiah Willard Gibbs - published series of papers showing the first two laws of thermodynamics could be computed analytically and graphically
• Gibbs Free Energy - a thermodynamics quantity equal to the enthalpy minus the product of the entropy and the absolute temperature
• 2 types of process

  1. Spontaneous Process
  2. Non-spontaneous Process
• Spontaneous Process 

  • time-evolution of a system which it releases free energy and moves to a lower more thermodynamically stable energy
  • No energy input is needed for the reaction to happen
• Non-spontaneous Process

  • Chemical reaction in which the change in free energy is positive, thus energy is absorbed
  • Needs energy for the reaction to happen
• Enthalpy - thermodynamics quantity which is equal to the total heat content of a system
• Entropy - lack of order or certainty or the degree of disorder or randomness in the system
• Features of Entropy

  1. Entropy and Unavailable energy
  2. Entropy and Disorder
  3. Entropy and Probability
• Entropy and unavailable energy 

  • Measure of the unavailable energy per unit temperature 
  • 2nd Law of Thermodynamics
• • Available energy - part of energy used for doing useful work
  • Unavailable energy - part of energy which cannot be converted into useful work
• Entropy and disorder 

  • Measure of the disorder or the randomness in the system
• Entropy and probability 

  • The entropy and thermodynamic probabilities are close related
• Second Law of Thermodynamics - states that for a thermodynamically defined process to occur the sum of entropies of the participating bodies must increase
• Nicolas Leonard Sadi Carnot - Father of thermodynamics because he proposed the second law of thermodynamics
• Reaction rate is dependent of the concentrations of the products. False
• An exothermic reaction absorbs heat energy. False
• In an endothermic reaction, the activation energy is decreased if temperature is decreased. False
• A decrease in activation energy makes the reaction rate faster. True
• Burning is an example of an endothermic reaction. False
• In an exothermic reaction, an increase in temperature increases its rate. True
• Catalyst undergoes permanent chemical change. False
• A promoter increases the rate of chemical reaction. True
• Concentration increases the collision of the particles of reacting substances. True