Chemical Reactions

• A chemical reaction is a process in which the properties of the original substance change into new substances with different physical and chemical properties.
• Evidences of Chemical Reaction

  • Change of color
  • Formation of gas
  • Temperature change
  • Change in smell
  • Formation of precipitate
• Product is produced in a chemical reaction
• Reactants enter a chemical reaction
• Types of Chemical Reactions

  • Synthesis/Combination Reactions
  • Decomposition Reaction
  • Single Displacement/Replacement
  • Double Displacement/Replacement
• The speed of a reaction is called the rate of reaction
• Some chemicals reactions are very fast while some are very slow
• Reactions take place when particles collide with a certain amount of energy
• The minimum amount of energy needed for the particles to react is called activation energy
• Collision theory is a way in which scientists explain how particles react
• In collision theory, particles are described as spheres
• Based on this theory, not all collisions between the molecules result in the formation of products
• Colliding molecules posses a minimum kinetic energy (activation energy), to start a chemical reaction.
• The reactant molecules should be in correct orientation when they collide
• Activation energy is required for the chemical reaction to proceed
• Conditions for chemical rxn to proceed

  • Particles must collide
  • Upon collision, orientation must be correct
  • Energy required to break the bonds must be enough
• Factors Affecting the Rate of Reaction

  • Temperature
  • Surface Area of Reactants
  • Concentration of Reactants
  • Presence of a Catalyst
• Nature is the phase of matter, its kind, its nature is a factor since it has its own identity and properties.
• Concentration is the amount of substance per unit volume
• Higher concentration means there is more of the solute in a solution
• High concentration means higher rate of reaction
• More particles of reactants, more chance of collision
• Higher temperature means higher kinetic energy
• Higher kinetic energy means faster movement of particles
• Surface area is the sum of the exposed regions of a substance
• Catalyst is a substance that increases the rate of a chemical reaction by providing an alternative pathway that has lower activation energy
• Exothermic reaction releases energy in the form of heat
• Endothermic reaction absorbs energy in the form of heat
• Spontaneous process occurs without ongoing outside intervention
• Do not confuse spontaneity with speed of reaction
• A reaction may be thermodynamically spontaneous but kinetically slow
• A catalyst will increase the rate of a spontaneous process but has no effect on a nonspontaneous process
• A nonspontaneous process is not impossible
• Nonspontaneous process requires an external energy supply
• For simple mechanical systems it is easy to see that the system tends toward the lowest potential energy
• For chemical systems we need a chemical potential that predicts the direction of the system
• Synthesis/Combination reactions occur when two or more substances combine and form a compound
• Decomposition reaction occurs when a single compound breaks down into two or more simpler products
• Single displacement/replacement reaction happens when one element replaces another element in a compound
• Double displacement/replacement this involves exchanging of ions to form a new compound