Reactivity 3.2 - 3.4
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What is oxidation
gain of oxygen, loss of electrons, increase in oxidation number
What is reduction
loss of oxygen, gain of electrons, decrease in oxidation number
Oxidising agent
causes oxidation, is reduced
Reducing agent
causes reduction, is oxidised
What are displacement reactions
more reactive metal replaces metal ion in the solution
What are electrochemical cells?
redox reactions occur, split into 2 half reactions, connected by a conducting wire
Ease of reduction in the period table
decreases down the group increased atomic radius, harder to attract electron
Two types of electrochemical cells, and their similarity/difference
voltaic and electrolytic both involve conversions between chemical and electric energy, but in opposite directions
Features of a voltaic cell
convert chemical -> electrical energy energy from spontaneous exothermic reaction released, then converted
Features of an electrolytic cell
convert electrical -> chemical energy energy provided to generate a non-spontaneous chemical reaction
What are electrodes and where are they used
electrodes are conductors of electricity used to make contact with non metallic part of a circuit voltaic + electrolytic need it
anode
oxidation
cathode
reduction
How does polarity work in the different electrochemical cells?
polarity - relative charge of two electrodes. more electrons -> more negative. electrons always flow from anode to cathode in voltaic cell: anode is negative, cathode is positive in electrolytic cell: anode is positive, cathode is negative
What is a redox equilibrium? And what determines to where it lies?
when a metal (electrode) is in contact with its ions (electrolyte) for a reactive metal: more to the right, since more is ionised for an unreactive metal: more to left, since it does not lose e- easily
Why do we need a salt bridge
charge accumulation (excess of e- at cathode) does not allow further flow of e- salt bridge completes internal circuit
In a voltaic cell, which metal is oxidised or reduced
higher in activity series - oxidised lower - reduced
What happens in the salt bridge
anions migrate to anode cations migrate to cathode keeping half-cells electrically neutral
striking visual difference betwen voltaic and electrolytic
voltaic - two half cells electrolytic - only one container
How do rechargeable batteries work
chemical reaction reversed by using an electrical current to drive reaction back to original state
types of rechargeable batteries
nickel-metal hydride lithium-ion
Describe a lithium ion battery
cathode: lithium metal oxide anode: lithium atoms absorbed onto graphite lattice electrolyte: non-aqueous solution containing Li+
Explain the discharge and recharge in a Li-ion battery
primary vs secondary cell
primary: one time use, not reversible reaction secondary: rechargeable, reversible