Chemistry - Redox Reactions and Electrochemistry
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- What does the law of conservation of charge say?
- It says that an electrical charge can be neither created nor destroyed
- What is oxidation?
- The loss of electrons
- What is reduction?
- The gain of electrons
- What does this law imply about oxidation and reduction?
- An isolated loss or gain of electrons cannot occur, but they must occur simultaneously, resulting in an electron transfer called a redox reaction
- What is an oxidizing agent?
- It causes another atom in a redox reaction to under oxidation, and is itself reduced
- What is a reducing agent?
- It causes the other atom to be reduced, and is it oxidized
- What are oxidation numbers?
- They are assigned to atoms in order to keep track of the redistribution of electrons during a chemical reaction
- What is it possible to determine from the oxidation numbers of the reactants and products?
- It is possible to determine how many electrons are gained or lost by each atom
- What are the rules for oxidation numbers?
- The oxidation number of free elements is zero, ex. N2, P4, S8 have zero oxidation numbers. The oxidation number for a monatomic ion is equal to the charge of the ion
- What is the half-reaction method?
- It is the most common method for balancing redox equation
- What is it also known as?
- It is also known as the ion-electron method
- What are the steps?
- Separate the two half reactions. Balance the atoms of each half reaction. First balance all atoms except H and O. In an acidic solution, add H2O to balance the O atoms, and then add H+ to balance the H atoms. In a basic solution, use OH- and H2O to balance the Os and Hs. Balance the charges of each half-reaction
- What are galvanic cells?
- They are also known as voltaic cells, and they are one of the two types of electrochemical cells. Galvanic cells are spontaneous
- Where do nonspontaneous reactions take place?
- They take place in electrolytic cells
- The electrode at which oxidation occurs is called what?
- It is called the anode
- What is the electrode where reduction occurs?
- It is called the cathode
- Does a redox reaction occurring in a galvanic cell have a negative G or a positive G?
- It has a negative G
- What are galvanic cell reactions used for?
- They supply energy and are used to do work
- How can the energy be harnessed?
- It can be harnessed by placing the oxidation and reduction half-reactions in separate containers called half-cells
- How are the half-cells connected?
- They are connected by an apparatus that allows for flow of electrons
- What does a salt bridge do?
- A salt bridge allows the charge gradient to be dissipated, which permits the exchange of cations and anions
- What does a salt bridge usually contain?
- It usually contains an inert electrolyte, usually KCL or NH4NO3, whose ions will not react with the electrodes or with the ions in solution
- Which direction do electrons flow?
- They flow from the anode through the wire and the voltmeter toward the cathode
- What is a cell diagram?
- It is a shorthand notation representing the reactions in an electrochemical cell
- What are the rules used in constructing a cell diagram?
- The reactants and products are always listed from left to right in the form: Anode | anode solution || cathode solution | cathode. A single vertical line indicates a phase boundary. A double vertical line indicates the presence of a salt bridge or some other type of barrier
- How are the oxidation and reduction half-reactions usually placed in an electrolytic cell?
- They are usually placed in one container
- What did Faraday say about the behavior of electrolytic cells?
- He said that the amount of chemical change induced in an electrolytic cell is directly proportional to the number of moles of electrons that are exchanged during a redox reaction
- What does one electron carry the charge of?
- It carries it as 1.6x10-19 coulombs ©
- What is one Faraday (F) equal to?
- It is equivalent to the amount of charge contained in one mole of electrons
- What is it?
- 1F = 96,487 coulombs, or J/V
- What is the anode of an electrolytic cell considered?
- It is considered positive
- Why?
- Because the spontaneous oxidation reaction that takes place at the galvanic cell’s anode is the original source of that cell’s negative charge
- What is the anode of a galvanic cell considered?
- It is considered negative
- What does this mean?
- It means it is the source of electrons
- Where does oxidation take place in both types of cells?
- It takes place at the anode
- How do electrons always flow through the wire?
- They always flow through the wire from the anode to the cathode
- In a galvanic cell, how is charge spontaneously created?
- It is spontaneously created as electrons are released by the oxidizing species at the anode
- In an electrolytic cell, where are the electrons forced through?
- They are forced through the cathode where they encounter the species which is to be reduced
- What is it here that provides electrons?
- The cathode provides electrons
- What does this make the cathode of an electrolytic cell?
- It is considered the negative electrode
- What is the mnemonic that shows what a cathode attracts?
- A CAThode attracts CATions
- What allows you to determine which species in a reaction that will be oxidized or reduced?
- The reduction potential of each species
- What is this defined as?
- It is defined as the tendency of a species to acquire electrons and be reduced
- What is the standard hydrogen electrode?
- It is what all reduction potentials are judged against. It is given a potential of 0.00 volts
- What is the standard reduction potential?
- It is measured under standard conditions: 25C, a 1M concentration for each ion participating in the reaction, a partial pressure of 1 atm for each gas that is part of the reaction, and metals in their pure state
- What can the relative reactivity’s of different half-cells be compared to predict?
- They can be compared to predict the direction of electron flow
- What does a higher E mean?
- It means a greater tendency for reduction to occur
- What does a lower E mean?
- It means a greater tendency for oxidation to occur
- What are standard reduction potentials also used to calculate?
- The standard electromotive force of a reaction
- What is that?
- It is the difference in potential between two half-cells
- What is the EMF of a reaction?
- It is determined by adding the standard reduction potential of the reduced species and the standard oxidation potential of the oxidized species
- Do you multiply the number of moles oxidized or reduced when adding standard potentials?
- No
- If the EMF is negative, is the cell an electrolytic or galvanic cell?
- If the EMF is negative, it is electrolytic