CHEM 2 (4TH QUARTERLY)

• Half life – It is the time taken for half of the amount a radioactive atoms to decay.
• Chemical Equilibrium – a state in which the rates of the forward and reverse reactions are equal and the concentration of the reactants and products remain constant.
• Concentrations of solid and liquid are not considered because they are constant.
• As the system approaches equilibrium, both the forward and reverse reactions are occurring.
• Partial pressure is proportional to concentration.
• Reaction Quotient (Q) – the ratio of the initial concentration of the products to the initial concentrations of the reactants using the equilibrium expression.
• Le Chatelier’s Principle - When a system at equilibrium is stressed, the system works to restore equilibrium.
• Stresses that affects the system equilibrium:

  1. Changes in the concentration of reactants and products
  2. Changes to the pressure (for gas systems)
  3. Changes to temperature
• Le Chatelier’s Principle: Whenever you try to increase something, the system will try to decrease it.
• Transfer of a proton (H+) from one species to another - is the essential feature of an acid-base reaction.
• Bronsted Lowry Acid - Proton (H+) Donor
• Bronsted Lowry Base - Proton (H+) Acceptor
• Water is ampoteric - can act as an acid or a base.
• Conjugate Acid - the product that results from protonation of a Bronsted-Lowry base.
• Conjugate Base - the anion that results from deprotonation of a Bronsted-Lowry acid.
• Strong acids are completely dissociated or ionizes in water. Their conjugate bases are weak.
• Weak acids only dissociate partially in water. Their conjugate bases are strong.
• The stronger a base, the weaker its conjugate acid.
• The weaker a base, the stronger its conjugate acid.
• In any acid-base reaction, the equilibrium will favor the reaction that moves the proton to the stronger base.
• pH - a measure of the acidity or the basicity of an aqueous solution.
• Pure water at 25 °C - has a pH of 7.00 and is neutral—neither acidic nor basic. Its concentration of H+ ions is exactly equal to the OH− (hydroxide) ion concentration.
• A buffer is a solution that can resist changes in pH when small amounts of acid or base is added. It is a mixture of a weak acid and its salt of a strong base (an acidic buffer) OR it is a mixture of a weak base and its salt of a strong acid (a basic buffer).
• Buffers are made up of a weak acid and its conjugate base (or a weak base and its conjugate acid).
• Solubility is the amount of solute that can be dissolved in a given amount of solvent.
• Very small amount of soluble salts are completely dissolved in saturated aqueous solution.
• Electrochemistry - is defined as the branch of chemistry that examines the phenomena resulting from combined chemical and electrical effects.
• Oxidation-Reduction Reaction - describes all chemical reactions in which there is a net change in atomic charge. Also known as “ Redox “ reaction. It is the movement of electrons between atoms.
• OIL - Oxidation is the loss of electrons.
• RIG - Reduction is the gain of electrons.
• Oxidizing agent - does the oxidizing. The substance being reduced.
• Reducing agent - does the reducing. The substance being oxidized.
• If oxidation number increases - oxidation occurred.
• For a Binary Ionic Compound, the O.N. is equivalent to the ionic charge.
• For Covalent Compounds or Polyatomic Ions, the O.N. is less obvious and can be determined by a given set of rules.
• If pKa increases, acid strength decreases.
• According to Le Chatelier's Principle, the system will not shift to the direction where there is stress.
• A system is in equilibrium when the forward and reverse reactions are occurring at the same time.
• Catalyst will not affect the position of an equilibrium.
• If Q>K, shift to the left.