Electrochemistry Flashcards
What is Electrochemistry?
A branch of chemistry which deals with the study of production of electricity happening from chemical reactions.
What are Redox Reactions?
A chemical reaction in which electrons are used by one substance and gained by another is Redox Reactions.
What are Galvanic Cells?
Electrochemical cells which convert the chemical energy of spontaneous redox reactions into electrical energy are called galvanic or voltaic cells.
Explain how oxidation and reduction generates electricity?
Oxidation occurs at anode whereas reduction occurs at cathode, they both result in the development of potential difference between the two half cells and hence, generate electricity.
How does a Daniell cell work?
It consists of two dissimilar electrodes i.e. zinc and copper. The zinc rod is dipped in zinc sulfate solution and the rod in a copper sulfate solution. The zinc electrode is the oxidation half-cell and the copper electrode is the reduction half-cell.
Zn(s) + Cu²⁺ (aq) — Zn²⁺ (aq) + Cu(s)
It has an electric potential of 1.1V.
What happens when the external potential of a Daniell cell is lower than 1.1V?
When this happens the electrons flow from Zn to Cu rod and current from Cu to Zn rod. Zinc then dissolves at anode and copper deposits at the cathode.
What happens when the external potential of a Daniell cell is equal to 1.1V?
Chemical reactions in the cell stop and there is no flow of electrons or current.
What happens when the external potential of a Daniell cell is more than 1.1V?
The reactions get reversed which also reverses the polarity of the electrodes. This cell is called an electrolytic cell.
What is a Salt-Bridge?
It is a U-shaped tube containing electrolytes (KCl, KNO³, NH⁴Cl) mixed with some kind of gel. It maintains electrical neutrality of solutions in each of the respective half-cells.
What is Electrode Potential?
Potential difference between electrode and electrolyte in an electrochemical cell.
What is Oxidation Potential?
The oxidation potential is when the metal electrode loses electrons and becomes oxidized.
What is Reduction Potential?
Metal ions usually leave the electrolyte and deposit at the electrode causing the metal to undergo reduction.
Explain the Cell potential.
The potential difference between two half-cells.
E° (cell) = E° (cathode) - E° (anode)
What does Cell potential depend upon?
1) Nature of metal and its ions
2) Concentrations of electrolytes
3) Temperature
What is Standard Hydrogen Electrode?
An arbitrary value that is given to a half cell to assign values to other half cells. Its value is zero.
Pt(s) | H2(g) | H⁺(g)
Explain applications of Electrochemical Series.
Shows stability in reduced form.
Negative, Reducing agent.
Positive, Oxidizing agent.
Tells feasibility of reaction, if negative will not proceed.
Nature of electrode, higher E° value is cathode lower is anode.
What is Nerst Equation?
Under standard conditions,
E (Mn⁺/M) = E° (Mn⁺/M) - RT/nF ln[1]/[Mn⁺]
For EMF of a cell,
E (cell) = E° (cell) - 0.0592log[Zn⁺²]/[Cu⁺²]
What is the Equilibrium Constant from the Nerst equation?
In general at equilibrium,
E° (cell) = 2.303 RT/nF log Kc
What is Gibbs energy for an Electrochemical cell?
It is given by,
ΔrG° = - 2.303 RT log Kc
What is Resistance and Resistivity?
Resistance is the hindrance in the flow of current provided by the conductor while resistivity is defined as resistance provided by a conductor of 1m length and cross-sectional area of 1m².
What is Conductance and Conductivity?
The ease with which current flows in a conductor.
G = kA/l
The inverse of resistivity is called conductivity.
k= G x l/A (cell constant)
What are the factors affecting the conductivity of electrolytic solutions?
1) Nature of the electrolyte
2) Size of ions and their solvation
3) Nature of solvent and its viscosity
4) Concentration of the electrolyte in the solution
5) Temperature
What is a cell constant?
The quantity l/A is called a cell constant.
G* = R x k
What is Molar Conductivity?
Conductance of solution containing one mole of electrolyte kept between two electrodes having a cross-sectional area and unit length between them.
Λm = k×1000/M
What is molar conductivity for strong electrolytes?
Strong electrolytes completely disassociate at all concentrations so it increases slowly with dilution.
Λm = Λm – A√c
What is limiting molar conductivity?
It is when the concentration approaches zero, the molar conductivity reaches a limiting value.
What is molar conductivity for weak electrolytes?
It is used by measuring Kohlrausch’s law as it increases steeply first and suddenly afterward becomes parallel with the graph.
What is Kohlrauch’s law?
It states that the limiting molar conductivity of an electrolyte is the sum of the individual contributions of the cation and anion of the electrolyte.
Λ°m = v+λ°+ + v-λ°-
What is an electrolytic cell?
Cells in which electricity is used to bring about a reaction. In this copper gets oxidized at the anode and deposited at the cathode causing reduction.
At anode,
Cu (s) → Cu2+ (s) + 2e-
At cathode,
Cu2+ (aq) + 2e- → Cu (s)
What is Faraday’s first law?
Chemical deposition at any electrode is directly proportional to the quantity of electricity passed through the electrolyte.
w = Zit
What is Faraday’s second law?
When the same quantity of electricity is passed through different electrolytes connected in a series, the weights of different substances liberated at the electrodes are directly proportional to their equivalent weight.
w1/E1 = w2/E2
What is Faraday’s Constant?
The amount of electricity required for oxidation and reduction depends on the stoichiometry of the electrode reaction.
Its value is 96500 mol⁻¹
What do the products of Electrolysis depend upon?
1) Nature of material being electrolyzed.
2) Types of electrodes being used.
3) Nature of species present in electrolytic cells.
4) Kinetic barrier or overvoltage.
