Redox reactions in the world: Cars

Within a car there are many parts

And in those parts, there are 3 particular ones, the Engine, the Battery and the Catalytic Converter, in which redox reactions happen

The Engine:

external image 4StrokeEngine_Ortho_3D_Small.gif

The engine is made up of many fuel injection chambers (like the one shown in the diagram above).

A combustion reaction happens within the chamber, which moves the piston below, thus providing energy for the car to run.

The redox reaction (addition/reduction of oxygen) is as follows:

2C8H18 + 25O2 => 16CO2 + 18H2O

However, the combustion is often incomplete, and in that case the reaction will be as such:

C8H18 + 8.5O2 => 8CO + 9H2O

The Battery:

car_battery.jpg lead_acid_battery.jpg
A Lead-Acid battery is used in a car, and the redox reaction in it is similar to that of a voltaic cell.

The component of the baterry are as follows:

Anode: Lead
Cathode: Lead Oxide
Electrolyte: Sulfuric acid

As sulfuric acid is a stong acid, it dissociates partially even before it is added to the battery

H2SO4 ==> H+ +HSO4-

As the battery discharges, the following half reaction (reduction) takes place at the anode:

Pb + HSO4 → PbSO4 + H+ + 2e

The 2 new electrons at the anode are then transported to the cathode through the wire, resulting in a electric current. The following half reaction (oxidation) then takes place at the cathode:

PbO2+3H ++HSO4+2e →PbSO4+2H2O

In the end, the full redox reaction that happens is:


The Catalytic Converter:


The catalytic converter processes the dirty exhaust gas before releasing it into the environment, so as to reduce the impact made to the environment. it does so through a three way reduction system.

1) The beads/layers of metallic catalysts such as platinum and rhodium reduces the nitrogen oxide (decomposition, loss of oxygen)

2NOx → xO2 + N2

2) The carbon monoxides go through oxidation (combustion) in the high temperature surroundings to form carbon dioxide

2CO + O2 → 2CO2

3) The unburnt hydrocarbons go through oxidation by combustion in the high temperature surroundings, forming the same process observed in the engine.

CxH2x+2 + [(3x+1)/2]O2 → xCO2 + (x+1)H2O

However, there is one flaw about this process: that it can only take place in high temperatures, hence there is the emission of harmful gases when the car has just started up, and it only stops when the catalytic converter has reached a certain temperature.