Galvanic Cells

What are electrochemical cells

a device in which chemical energy is converted into electrical energy and vice versa.

what is a galvanic cell

a voltaic cell
a type of electrochemical cell in which chemical energy is converted into electrical energy (only one way)

how does electrical current flow through the external circuit

movement of electrons through the wire

how does current flow in the internal circuit

movement of ions

which way do electrons flow

anode to cathode

what does each half cell contain

a reactant and its oxidised or reduced product.

what is the purpose of a salt bridge

to complete the circuit and allow the flow of ions to prevents a build up of charge in the two half-cells, preventing direct contact of the oxidising and reducing agents while permitting the ions to flow through it

what does a salt bridge contain

a strong electrolyte which always forms soluble salts when in contact with other solutions

what way do cations/anions flow in a salt bridge

cations to cathode, anions to anode

what is the purpose of an inert electrode

to conduct electrons without reacting with surrounding ions
e.g. graphite, platinum

metal/metal ion half cell

metal electrode, metal cation solution

metal ion/metal ion half cell

inert electode, metal ion solution of 2 different oxidation states

non-metal/non-metal ion half cell

inert electrode, non-metal ion solution of 2 different oxidation states

non-metal gas/non-metal ion half cell

inert electrode in gas inlet, solution of non-metal ions

what is EMF

Electromotive force/potential difference (voltage)

what does the voltage which a cell generates depend on

the nature and concentration/gas pressure of the reacting substances.

standard conditions of which potential differences are measured under

aqueous concentration of 1molL-1, temperature 298K (25C), gas pressure 100.0 kPa

how are standard reduction potentials obtained

by measuring the voltage when attached to a reference hydrogen half-cell

how to calculate E0 of a cell

E0reduction + E0oxidation

How to tell if a reaction is spontaneous

oxidising agent must be positioned above the reducing agent, E0 is positive

types of galvanic cells

primary cell, secondary cell, fuel cells

what is the overall voltage of the reactions in a galvanic cell

positive

when might no reaction occur even if E0 is positive

if there is a very high activation energy

what is a primary cell

non-rechargeable cells e.g dry cell

what is a secondary cell

rechargable cell
e.g car battery, laptop

electrolyte in a car battery

sulfuric acid

advantages of alkaline cells

Needs less electrolyte, more reactant can be included, cost effective for devices which need high currents intermittently.

dry corrosion

metal + oxygen -> metal oxide
e.g. sodium must be stored in oil to prevent contact with oxygen

wet corrosion

corrosion in the presence of moisture

corrosion surface protection - covering

Cover the surface to prevent contact of the metal with oxygen or moisture e.g. oil on bike chains

corrosion surface protection - alloying

Alloy the metal with small quantities of other metals e.g. Cr, Ni, Mn etc. These metals oxidise slightly in air by the oxide coating is continuous and unreactive, protecting the metal from further oxidation

corrosion surface protection - electroplating

Coat the metal with thin layers of less reactive metals e.g. steel coated with tin in 'tin cans'

corrosion electrochemical protection - cathodic

Low voltage DC power supply gives the metal a negative charge, reducing the ability for the metal to oxidise and lose electrons

corrosion electrochemical protection - sacrificial

Coating the metal in a more reactive metal so the more reactive metal loses electrons in preference to the less reactive one, protecting it

How do salt bridges prevent a build up of charge

If the oxidation half cell produces excess cations then the negative ions will move into that cell to balance the charge, vice versa.