Electrochemical Reactions Flashcards
Oxidation
A loss of electrons, an increase in ON
Reduction
A gain of electrons, a decrease in ON
Galvanic cell (voltaic cell)
An electrochemical cell in which chemical energy is converted into electrical energy.
This is as a result of a self-sustaining spontaneous reaction.
Electrolytic cell
An electrochemical cell in which electrical energy is converted into chemical energy.
This occurs by means of a non-spontaneous redox reaction using a supply of electrical energy.
Oxidising agent
A substance that is reduced/gains electrons in a redox reaction
Reducing agent
A substance that is oxidised/loses electrons in a redox reaction
Electrode
A solid electric conductor through which an electric current enters of leaves an electrolytic cell or other medium
Anode
The electrode where oxidation takes places
ANOX
Cathode
The electrode where reduction takes place
REDCAT
Electrolyte
A solution/liquid dissolved substance that conducts electricity through the movement of ions
A solution which is able to conduct electrical charge due to the movement of free ions through the solution
Electrolysis
The chemical process in which electrical energy is converted into chemical energy OR
The use of electrical energy to produce a chemical change.
Spectator ion
An ion which does not chemically participate in the reaction, so can be ignored when considering the electrochemistry taking place in a cell
Standard electrode potential
The voltage measure for a half cell under standard conditions when the half cell is connected to a standard hydrogen electrode to form a galvanic cell
What is the direction of current flow in a galvanic cell
Always from anode (-) to cathode (+)
Negative electrode to positive electrode
What is the direction of current flow in an electrolytic cell
and WHY
From positive to negative.
The anode is now the positive electrode, the cathode is now the negative electrode
WHY?
due to the fact that this is how the electrodes are connected to the external power supply that supplies the electrical energy to t sustain the electrochemical reaction.
Salt bridge
a tube containing an electrolyte/ filled with a saturated soution of salts (4) providing electrical contact between two solutions.
What is inside a salt bridge and why those specific electrolyte solutions
A saturated solution of:
- potassium chloride (KCl)
- sodium chloride (NaCl)
- potassium nitrate (KNO3)
- sodium sulphate (Na2SO4)
These electrolytes used because they are generally unreactive towards the chemical substances in the individual beakers.
2 functions of a salt bridge (in a galvanic cell)
- To connect the two half cells together to complete the circuit
- To maintain ionic neutrality in each of the half cells
Do galvanic cells use direct redox reactions and why?
No, Galvanic cells use indirect redox reaction because chemical contents in each cell do not mix directly.
Half-cell
A half-cell is a structure that contains a conductive electrode and a surrounding conductive electrolyte
Corrosion (in galvanic cell process)
Process whereby ions are introduced onto the electrolyte form the metal electrode and thus causing that metal electrode to decrease in mass
Plating (in galvanic cell process)
When metal ions form and coat he metal electrode. These ions are removed from the electrolyte solution and are transported to the metal electrode thus increasing its mass.
on table 4B which direction is oxidation and which reduction (horizontally)
Reduction –> left to right
Oxidation –> right to left
In an electrolytic cell electrodes are generally made of… why?
Carbon (graphite)
WHY?
Metals like platinum can be used as electrodes but they are quite expensive. A cheaper alternative that is resistant to corrosion is graphite. As graphite conducts electricity and is resistant to corrosion it is used to make electrodes for electrolysis.
Energy conversion in galvanic cell
Chemical energy to electrical energy
Energy conversion in electrolytic cell
Electrical energy to chemical energy
Direct flow of electric flow of current
Electrons flow through the external circuit from anode to cathode / from negative to positive
Electron current
Conventional current
From positive to negative in though a circuit, in the opposite of the flow of electrons
What is cell notation
Cell notation is the simplest and most convenient way and is an abbreviated representation of the reactions taking place in a galvanic cell.
What are the standard conditions for the measurement of standard electrode potentials
- Temperature 298 K or 25 °C
- Concentration of solutions must be 1 mol.dm-3
- Pressure of 101,3 kPa (atmospheric pressure) is a gaseous half cell is used
