U2AoS1 - Redox Reactions Flashcards
What are Redox Reactions?
A reaction that involves the transfer of electrons.
Processes of oxidation and reduction
What are the types of redox reactions?
- Addition/combination reaction
- Decomposition reaction
- Displacement reaction
- Combustion reaction
What is an addition reaction?
A + B – C
What is a decomposition reaction?
c - A + B
What is a displacement reaction?
A + BC – B + AC
What is oxidation?
Loss of electrons
What is reduction?
Gain of electrons
Half equation
electrons shown as either a product or reactant depending on oxidation or reduction
Reductant
Substance that causes another to be reduced and itself oxidised
Oxidant
Substance which causes another to be oxidised and itself reduced
Overall balance equation
Shows products/reactants but not electrons
Ionic equation
Two half equations written together
- no spectator ions
- must be balanced when two added together
Conjugate redox pair
Pair differ by one or more electrons
Oxidised form written first
Are ionic compounds formed through redox reactions?
Transfer of electrons hence, yes
Covalent molecular compounds… are they redox?
- can be involved despite shared
- partial electron transfer, unequal sharing of electrons
Oxidation numbers
determines if a redox reaction has occured
Oxidation number increases
Oxidised
Oxidation number decreases
Reduced
Oxidation number of free elements
O
Oxidation number of ionic compounds
Charge of the ion
Polyatomic oxidation numbers
Sum is equal to the charge on the ion
Oxygen and Hydrogen Numbers
usually, -2 and +1
UNDER ACIDIC CONDITIONS
KOHES
- key elements
- oxygen balanced by water
- hydrogen by H+ ions
- electrons added
- states
Overall ionic equations
- balance no.
- add half equations
- cancel species on both sides
Reactivity of metals
A will only replace B if A is more reactive. A is oxidised and B is reduced
Forwards Reaction
Reduction
Backwards Reaction
Oxidisation
Strong oxidants
accept electrons more readily
Strong reductants
donate protons more readily
What is a Galvanic Cell?
Converts chemical energy to electrical energy from spontaneous redox reactions taking place in the cell
What is a laboratory galvanic cell?
Reactants separated into half cells connected with wire and a salt bridge to complete the circuit and allow for movement of electrons
Half cells
contains a conjugate redox pair, electrodes must conduct electricity
Anode
negative polarity (oxidation) will decrease mass and increase color intensity
Cathode
positive polarity will increase in size
If conjugate redox pair is metal
metal electrode
If it does not contain metal
inert electrode (graphite or platnum) for fe4+ and sn 2+
If it is a gas
Gas electrode platinum used
Two electrolytes
Solution which contains free moving ions
Salt bridge
- connects/completes the circuit
- provides ions to compensate for those lost/gained during a reation
KNO3
Voltmeter
records voltage (potential difference) produced by cell
External circuit
electrodes+ wire
Internal circuit
salt bridge + electrodes
