Unit 5: Electrochemistry Flashcards
Metals love to ____
Oxidize
____ is a reaction in which e- are lost
Oxidation
Oxidation-reduction (redox) reactions involve a transfer of ____.
Electrons
_____ is the branch of chemistry which is concerned with the conversion of chemical energy to electrical energy, and vice versa.
Electrochemistry
A(n) _____ _____ is a half-reaction in which a species loses electrons.
Oxidation reaction
A(n) _____ _____ is a half-reaction in which a species gains electrons.
Reduction reaction
For every reduction reaction there must be an accompanying ____ ____.
Oxidation reaction
For every oxidation reaction there must be an accompanying ____ ____.
Reduction reaction
A reaction involving the loss and gain of electrons is called a ______-______ ______.
Reduction-oxidation reaction
A reduction-oxidation reaction is also called a ____ reaction
Redox
You can be certain you are dealing with a redox reaction any time you see that an atom or ion has changed ____ during the reaction
Charge
The oxidizing agent is ____ during the reaction
Reduced
The reducing agent is ____ during the reaction
Oxidized
A species being oxidized becomes more ____ charged
Positively
A species being reduced becomes more ____ charged
Negatively
Oxidation reactions are often the attachment of ____ to ____
Oxygen
Metals
The reduction process removes ____ from the metal compounds, leaving more or less pure metal behind
Oxygen
An oxidation number is the charge that an atom would posses if….
The species containing the atom were made of ions
The rule which governs oxidation numbers is
The sum of the positive charges and the negative charges must equal the overall charge on the species
The oxidation number of an atom in its elemental form is ____.
ZERO
The oxidation number of a monatomic ion is ….
The charge on the ion
When referring to an isolated half reaction, use ______ arrows to show that the reaction can go….
Equilibrium
Forward or backward
If the half reaction is made to undergo either reduction or oxidation as a result of being part of a redox reaction the use a ______ reaction arrow
One way
If two half cells are joined, the half reaction ____ on the chart will undego reduction and the one _____ chart will undergo oxidation
Higher
Lower
If both reactants are only found on the left of the table or both reactants are only found on the right then….
No reaction is possible
If the reactant to be reduced (left side) is higher on the table than the reactant to be oxidized (right side) the reaction will ____ _____
Occur (spontaneously)
If the reactant to be reduced (left side) is lower on the table than the reactant to be oxidized (right side) the reaction will ____ _____
Not occur
A disproportionation reaction is…
A redox reaction in which the same species is both reduced and oxidized
A reaction will be spontaneous if and only if there is a reactant to be reduced which is ______ a reactant to be oxidized
Above
An increase in oxidation number in one species must be balanced by a corresponding ____ in oxidation number in a second species
Decrease
In any redox equation the overall change in oxidation numbers must be ____
Zero
An electrode is (in general terms)….
A conductor at which a half reaction occurs
At which electrode does oxidation take place?
Anode
At which electrode does reduction take place?
Cathode
The electrode to which anions travel is?
The anode
A cathode ____ electrons from/to a substance being ____. The cathode receives its electrons through the wire from the ____
Supplies
Reduced
Anode
Electrons flow from the ____ to the ____
Anode
Cathode
The electrons are forced through the wire in an electrochemical cell because….
The reactants are separated
Only ____ flow in the solution in an electrochemical cell
Ions
The number of electrons involved in the oxidation reaction must equal….
The number of electrons involved in the reduction reaction
As positive ions are formed at the anode they accumulate around the anode. This excess of positive charge is depleted by…. (2 factors)
1) random movement of the positive ion away from the anode due to the fact that there is a higher probability that the ion will move to the area of the lower concentration of the ion
2) movement of the negative ions toward the anode (due to its positivity)
As the positive ions around the cathode are depleted by the reduction of them, the amount of positive charge is decreased around the cathode. The resulting deficiency of positive charge is corrected by…. (2 factors)
1) the movement of the positive ions towards the cathode by random movement. There is a great possibility that the ions will move into a low concentration from a high concentration
2) movement of negative ions away from the cathode. The greater amount of positive charge at the anode end of the cell will attract the negative ions toward the anode
The tendency of electrons to flow in an electrochemical cell is called _____ or ____ ____ to do work.
Voltage
Electric potential
The _____ is the work done per electron transferred
Voltage
E° =….
The STANDARD REDUCTION POTENTIAL, in volts.
The “o” in the E° implies this is a ____ _____
STANDARD STATE
An electrochemical cell is said to be at STANDARD STATE if… (4 things)
1) it is at 25°
2) all gasses are at 101.3 KPa (1 atm)
3) all elements are in their standard states (that is, their normal phase at 25°c)
4) there exists a 1M concentration for ALL solutions involved in the half cell (both on the reactants and products side)
Platinum is used because it is an ____ electrode.
Inert
Being a inert electrode means…
It doesn’t react but it conducts electrons and allows the reaction to occur at its surface
If a half reaction is reversed the sign of its E° value is ____.
Reversed
If two half reactions can be added together to give a redox equation, the voltages associated with the half reactions can be ____
Added
The potential of an electrochemical cell is just the difference between the half-cell voltages for the…..
Reduction reaction and the oxidation reaction.
E°red - E°ox = ?
E°cell
If E°cell is positive for a redox reaction the reaction is expected to be_____.
Spontaneous
If E°cell is negative for a redox reaction, the reaction is _____.
Non-spontaneous
____ is the work done per electron so DO NOT multiply the E° value
Voltage
If a reaction occurs in an acidic solution, the reduction of ____ may be a possible reaction and must be considered along with any other reductions possible
H+ (at 0.00V)
If a reaction occurs in an neutral solution, the reduction of ____ may be a possible reaction and must be considered along with any other reductions possible
Neutral water (at -0.41V)
The surface are of an electrode has _______ (no effect/some effect) on the cell potential
No effect
When the surface area of an electrode is increased, the reaction rate at the electrode ______. That is, the number of electrons per second being transferred ______.
Increases
Increases
The increased reaction rate, due to increased surface area, _____ (does/ does not) increase the cell voltage.
Does not
How can you increase the amount of time a battery will operate?
Increase the amount of electron material
When the difference in reduction potentials is zero (Ecell=0)….
The reaction is at equilibrium
If the difference in reduction potentials is zero then the reaction is….
At equilibrium
Name 4 ways to prevent corrosion
1) apply a protective layer
2) apply a metal which is corrosion resistant to the surface of the original metal
3) cathodic protection
4) change the conditions in the chemical surroundings so as to lower the tendency of the surrounding to reduce
Cathodic protection is…
The process of protecting a substance from unwanted oxidation by connecting it to a substance having a higher tendency to oxidize
An _____ or ______ is an apparatus in which electrolysis can occur.
Electrolytic cell
Electrolysis cell
_____ supplies energy to non-spontaneous electrochemical reactions (E°cell
Electrolysis
Electrolysis is the process of….
Supplying electrical energy to a molten ionic compound or a solution containing ions so as to produce a chemical change
What is a binary salt
A binary salt is a salt made of only two different elements
In a simple electrolytic cell (electrolysis of a molten binary salt) there is no need for a salt bridge or a porous barrier to keep the reactants separated because….
No spontaneous reaction occurs between the reactants
In a simple electrolytic cell (electrolysis of a molten binary salt) what are the anode and cathode made of?
both anode and cathode are made of inert materials such as platinum or carbon
The anode and cathode in a simple electrolytic cell are connected by?
A wire with a DC current battery in its center
During the electrolysis of aqueous solutions what must you always consider?
You must always consider the possibility that H2O may oxidize and/or reduce
The preferred reaction (in electrolysis of aqueous solutions) will be the one requiring the least…..
Voltage input
Which half reactions are preferred?
The half reactions that have the greatest tendency to reduce and the greatest tendency to oxidize
Electrolysis of aqueous solutions containing Cl- or Br- will produce?
Cl2 or Br2 at the anode
Electroplating is….
An electrolytic process in which a metal is reduced or “plated out” at a cathode
In electroplating: the cathode is made of?
The material which will receive the metal plating
In electroplating: the ______ solution contains ions of the metal which is to be “plated” onto the carthode
Electroplating
In electroplating what is the anode made of? (2 possible answers)
1) the anode may be made of the same metal which is to be “plated out” onto the cathode
2) the anode can also be an inert electrode (carbon or platinum)
Electrorefining is the process of….
Purifying metal by electrolysis
When several different reduction half reactions occur the one having the _____ tendency to accept electrons or the ____ reductions potential will occur preferentially.
Highest
Highest
When several different oxidation half reactions occur the one having the _____ tendency to lose electrons or the ____ reductions potential will occur preferentially.
Highest
Lowest
Any ion capable of being reduced will be a _______ ion if there is another ion in the same solution which has a greater tendency to be reduced
Spectator
Any ion capable of being oxidized will be a spectator ion if there is another ion in the same solution which has a _____ tendency to be _____
Greater
Oxidized
Which ions are generally spectator ions? (six ions)
Na+ K+ Ca2+ Mg2+ SO4 2- (in a neutral solution) Cl-
The anode _____ electrons from the substance being _____ and the electrons then move through the wire to the ____
Receive
Oxidized
Cathode
