galvanic cells and fuel cells as energy

• 'Mg(s) >>> Mg^2+ + 2e', what type of half equation is this?

  Oxidation, as oxidation is loss of electrons and Magnesium loses 2 electrons in this equation + the electrons are added to the RHS further showing its an oxidation half equation.
• what is a conjugate redox pair?

  A pair of two species, one being oxidized and the other being reduced, that are involved in a redox reaction.
• what are reducing agents?

  Substances that donate electrons and undergo oxidation themselves.
• all solid metals by themselves have an oxidation number of?

  0
• what is the usual oxidation state of hydrogen?

  +1
• what is the usual oxidation state of oxygen?

  -2
• when trying to find wether an equation is a redox equation what do you look for?

  change in oxidation state
• why is a species that loses electrons considered oxidized?

  Because electrons are negatively charged, when a species is oxidised becoming "positive" with an overall "positive charge" it has lost its negative charge and therefore gained a positive charge.
• typically a gain in oxidation number means oxidation has occurred but what is an alternative way to measure oxidation?

  a gain in oxygen or a loss of hydrogen
• when something is in basic conditions, and you have H+(an acidic substance), what can you use when balancing the equation to counteract this?

  use 20H^- to balance out the H+
• Redox reactions


  Simultaneous oxidation and reduction processes, involving the transfer of one or more electrons between chemical species
• Oxidation number


  Number assigned to an atom that can be used to determine the movement of electrons in redox reactions
• Oxidation


  Chemical reaction in which a chemical species loses one or more electrons
• Reduction


  Chemical reaction in which a chemical species gains one or more electrons
• Oxidising agent


  Chemical species that oxidises another substance by accepting one or more electrons
• Reducing agent


  Chemical species that reduces another substance by donating one or more electrons
• Conjugate redox pair


  The electron donor (reactant/product) and its corresponding electron acceptor (product/reactant)
• Half-equation


  Reduction or oxidation equation of a complete redox reaction
• Overall redox equation


  Equation of a complete redox reaction combining reduction and oxidation half-equations
• Identifying redox reactions using oxidation numbers


  1. Determine the charge of the ion

  2. Sum of oxidation states in a neutral compound is 0

  3. Sum of oxidation states in a polyatomic ion is equal to the charge of the ion

  4. Oxidation state of a free element is always zero

  5. Oxidation state of hydrogen is normally +1 (except in metal hydrides where it is -1)

  6. Oxidation state of oxygen is normally -2 (except in peroxides where it is -1)
• • An increase in oxidation number indicates the atom has been oxidised (lost electrons)
  • A decrease in oxidation number indicates the atom has been reduced (gained electrons)
• • The more negative an oxidation state, the lower the oxidation state of the given atom
  • The more positive an oxidation state, the higher the oxidation state of the given atom
• Oxidation state


  The lower the oxidation state of the given atom, the lower it is. The more positive an oxidation state, the higher it is.
• 3A THEORY
• 3a redOx reaCTIOns
• When attempting to determine the oxidation state of an atom, it's important to note that the most electronegative atom in a compound or molecule will have a negative oxidation state.
• Overall oxidation states in a compound do not always have to be whole numbers.
• All free elements have an oxidation state of 0.
• Oxygen atoms in chemical compounds normally have an oxidation state of -2.
• The sum of the oxidation states of each element in a neutral compound will equal zero.
• Reducing agents undergo oxidation, causing their oxidation number to increase.
• Redox reactions involve the transfer of one or more electrons from one species to another.
• Oxidation reactions (loss of electrons) and reduction reactions (gain of electrons) occur simultaneously.
• A reducing agent causes another species to be reduced by donating one or more electrons to that species. Therefore, it is itself oxidised.
• An oxidising agent causes another species to be oxidised by accepting one or more electrons from that species. Therefore, it is itself reduced.
• A conjugate redox pair consists of an oxidising agent (reactant/product) and it's corresponding reducing agent (product/reactant).
• An increase in oxidation number (loss of negative charge) of a species indicates that species has undergone oxidation.
• A decrease in oxidation number (gain in negative charge) of a species indicates that species has undergone reduction.
• but this is not always the case
• Balancing charges in a chemical equation

  Electrons are added to the more positive side of the equation