External Revision: Unit 3, Topic 2 Flashcards
(67 cards)
Oxidation
Chemical reaction where species looses electrons
Reduction
Chemical reaction where species gains electron
What does a redox reaction involve
Transfer of electrons and is a combination of two different reactions occurring simultaneously.
Involves Reduction & oxidation which can’t occur without each other
Acronym for what happens to species in redox
Oxidation
Is
Loss
Reduction
Is
Gain
Fe ->Fe^2+ + 2e-
Is this oxidation or reduction
Oxidation
Is a species oxidised in a reduction or oxidation reaction?
Oxidation
Eg. Fe goes to Fe^2+ therefore Fe was oxidised
Zn^2+ -> 2e- + Zn
Is this reduction or oxidation
Reduction
Zn^2+ has been reduced
Which groups gain and loose electrons
Group 1 and 2 have low ionisation energy therefore loose electrons
Group 16 and 17 have high electronegitivity towards F, thus gain electrons
Oxidation agents
Species that cause other other species to loose electrons (undergo oxidation)
Reducing agents
Species that cause other species to gain electrons (undergo reduction)
Oxidation number
Number assigned to an atom in a substance used to determine the movement of electrons in redox reactions
Helps determine if redox reaction occurred
Highlights charge atoms have due to movement of electrons in redox reaction
List the oxidation number rules
Check favourited screenshots for answer
When does oxidation no. Increase and decrease
In redox reactions oxidation number changes
INCREASE:
when number gets larger, atom has undergone oxidation.
• The loss of electron(s) (a negative charge) results in an increase in oxidation number.
DECREASE:
when the number gets smaller, atom has undergone reduction.
• The gain of electron(s) (a negative charge) results in a decrease in oxidation number
Half equations
We express the oxidation and reduction reactions in a redox reaction through half equations.
For example:
• An oxidation half equation: K -> K+ + e-
• A reduction half equation: Cl2 + 2e- -> 2Cl-
When writing simple half equations, we are mainly trying to balance the number of atoms and overall charge of the half equation using electrons.
KOHES
Balancing half equations in Redox reactions involving polyatomic ions is complex.
‘KOHES’ helps determine the appropriate steps to balance complex half equations.
We only need to know how to do this in acidic conditions.
Key elements must be balanced
Oxygen atoms must be balanced
Hydrogen atoms must be balanced
Electrons must be added to balance charge
States must be included
What do you do when combining half equations
When combining oxidation and reduction half equations together to write a full redox equation, electrons from both half reactions must cancel out.
Must multiply each half equation by a factor to make sure that the number of electrons from both half equations are equal
What does metal reactivity refer to
Metals tendency to donate electrons and be ionised
Spontaneous redox reaction
Redox reaction that results in the release of energy.
strong oxidising agent will undergo reduction
strong reducing agent will undergo oxidation.
What does the metal reactivity show
The reactive series of metals orders reactivity from high to lowest
• These are expressed as reduction half equations for metal cations.
• The table is organised with:
– metals (solid) on the right hand side, and
sorted from most reactive at the top, to
least reactive at the bottom.
– metallic ions on the left hand side.
• Since lithium is shown to be the most reactive metal, it is the strongest reductant.
• Li+ is the weakest oxidant.
What happens in metal displacement reaction
Reactive metals can cause cations of other metals to be displaced from a solution containing the cations.
• The metals will undergo oxidation, resulting in the
cation undergoing reduction.
• This results in a spontaneous redox reaction.
– for this to occur ,we need to react a strong oxidising agent with a strong reducing agent.
– The position of the reducing agent needs to be higher on the reactivity table than the oxidising agent.
Corrosion
Wet = involves water
Dry = involves oxygen
To prevent, must coast with more reactive metal
Combustion
Exothermic reactions involving fuels + oxygen
CH4(g) + 2O2(g) -> CO2(g) + 2H2O(g)
What are Galvanic cells and how do they occur
A type of electrochemical cell that converts chemical to electrical energy
Done via spontaneous redox reactions
When you put a few cell together you get a battery
Other name for galvanic cell
Voltaic cell
