redox reactions

redox reactions

• a result of simultaneous reduction and oxidation

  • Oxidation - an increase in oxidation number (lose electrons) 

    • reductant is oxidised (provides electrons for the other substance to be reduced)

  • Reduction - a decrease in oxidation number (gain electrons)

    • oxidant is reduced (accepts electrons from the other substance)

rules for oxidation numbers

• ON for H in compounds with non metals is +1

• ON for oxygen in a compound is usually -2

balancing half-equations in basic/alkaline conditions when OH- is reactant or product

balance elements by adding OH- on both sides (amount depends on H+) → MAKE IT WATER and cancel it out if needs to 

reactivity series of metals 

top left → strongest oxidising agent

bottom left → weakest oxidising agent

top right → weakest reducing agent

bottom right → strongest reducing agent

electrochemical cell

a device which converts chemical energy to electrical energy or vice versa

Galvanic cell

a type of electrochemical cell which converts chemical energy to electrical energy

• separate the oxidation + reduction reactions into two different half-cells → allows electrons to move freely between them and produce electricity

indirect redox reaction is required (reactants are separate)

Construction of a galvanic cell

1. Two half cells THAT ARE SEPARATED

   • each half cell has an electrolyte solution and an electrode 

   • electrode with negative polarity → anode → oxidation

   • electrode with positive polarity → cathode → cathode

2. the two electrodes are connected with conducting wires → electrons flow through the wires to form the external circuit

3. salt bridge - any substance ions can flow through easily (two ends of the strip should dip inside the 2 electrolyte solutions) → internal circuit 

SPONTANEOUS CHEMICAL REACTION → production of electrical energy in electrochemical energy

electrolyte solution and an electrode

es - ionic compounds which are soluble (allow for charge to flow)

e - electrically conductive structures (allow for electrons to move from the ‘reaction’ to the outside of the cell)

Visual observations in Galvanic cell redox reaction

• anode gets smaller → where oxidation occurs, producing electrons that travel through an external circuit to the cathode, where reduction occurs

• cathode gets larger 

• use the data book for colour changes (oxidation + reduction)