R3.2

• Key processes in Redox: battery process, cellular respiration, photosynthesis, rusting, energy creation, separation of elements
• Proton transfers work with neutralization of acids and bases
• By listing oxidation states we can figure out what is getting reduced (gaining electrons=becoming more negative) and what is getting oxidized (losing electrons=becoming more positive)
• The species (reactant) getting oxidized will be the reducing agent and the species (reactant) getting reduced will be the oxidation agent
• 1/2 reactions show the oxidation and reduction of elements as follows;

  X -> (X^+1) + (e-) [oxidation]

  (Y^+2) +(2e-) ->Y [reduction]

  NOTE: products/reactants do not need to be neutral- just an example!!
• Rules for balancing redox reactions:

  1. Write half equations
  2. Balance non-hydrogen or oxygen elements
  3. Add water to the other side to balance oxygen
  4. Balance hydrogens by adding H+ on the other side
  5. Balance electron charges (lowest common multiple)
  6. For basic solutions, add OH- to both side corresponding to the number of H+ present (so they can combine to form water, and then water from the other side can cancel some of its molecules to create final expression)
• Neutralization reaction: H20 -> (H+) + (OH-)
• Solve waters, H+ and OH- like algebra= subtract like terms on opposite sides
• Short cut for base balancing:

  1. swap H2O and H+ places
  2. Turn H+ to OH-
• Disproporation is when the same element is undergoing both reduction and oxidation in one reaction
• Displacement reactions: Tarnishing of silver, changing color of copper, rusting of iron
• Refer to reactivity series for displacement as those with greater negative values (more preferred to be oxidized = more reactive) will be able to displace those with lower negative/reduction potential values
• Francium is the most reactive metal bcs it has low nuclear charge and low Ionization energy
• If X + Y is being reacted when X and Y are both on reactivity series, the reaction can only occur if Y is more reactive than X as Y is being added to X and needs to overpower it
• Reactivity encompasses number of valance electrons on species, shielding effect, nuclear charge, total charge, and group and period of species
• Electrons flow from anode (oxidation) to cathode (reduction) ALWAYS
• Electrochemical cells facilitate the flow of electrons between two electrodes immersed in two electrolytes (ions of the electrodes)
• Two types of electrochemical cells = voltaic and electrolytic cells
• voltaic cells have two separate half cells, a salt bridge to facilitate the flow of ions that balance charges at each terminal and allow for continued flow of electrons while separating the two solutions and reducing liquid junction potentials, an external wire for electron flow, and a voltmeter to observe electron flow
• voltaic cells work to convert chemical energy into electricity and is spontaneous and exothermic
• Because voltaic cells are spontaneous, the charge on the anode is negative and the charge of the cathode is positive as the anode (oxidized and lost electrons) will attract electrons that have too many electrons so they can both balance their charges which the opposite is true for the cathode
• In voltaic cells a | signifies a phase boundary and a || signifies the presence of a salt bridge in its notation
• Standard Hydrogen Electrode (SHE) is what we compared all other reactivities to
• Liquid junction potential: Voltage generated when solutions contact each other because they have unequal cation and anion movements across junction
• Cotton is usually placed at the ends of the salt bridge to prevent solution from traveling through the bridge and only allowing ions to do so
• Danielle cell/voltaic cell is an improvement of Alessandro's volta pile by separating into half cells = semi-permeable-diaphragm
• Ions in a voltaic cell are exchanged if they are inert and cations (positive ions) flow to positive terminal (cathode) while anions (negative ions) flow to negative terminal (anode)
• Reusable batteries can be represented as a reversible reaction- include lithium ions (cell phone batteries) and nickel hydride (A, AA, AAA batteries)- and can be reused but need to be replaced after a certain period of time
• Reusable batteries can be "re-charged" with a precise electrical current
• Electrolytic cells are non-spontaneous and endothermic, requiring a battery inputted in place of the voltmeter to send electrical charges and power reaction. Because of this, the cathode is unnaturally the negative terminal and the anode is the positive one though electrons still flow from the anode to the cathode.
• To mathematically quantify energy over time in electrochemical cells is to calculate the potential difference and electromotive force (EMF in voltaic cells)
• Adsorbption to form on the surface without infusion
• Inert: unreactive
• In electrolytic cells, the cathode adsorbs and the anode erodes into ions
• Standards are useful to base other measurements around and compare values
• A negative reduction potential signifies a tendency to be oxidized
• SHE needs to be at O volts, 1mol/dm3 of KCL, 298K and 100kPA, and with platinum metal for standard value
• The standard Cu value of reduction potential is +0.34 unless explicitly asked for another equation (multiple are available)
• The total potential difference (E[total]) of the electrochemical cell is calculated as follows: E[cathode] - E[anode]
• More than 1 ion can be attracted to an electrode so choosing if between potential difference values