Spontenaity of Combustion Reactions

 

As seen with liquid gas in a can or wood in a pile combustion does not just happen without outside intervention. A high temperature ignition is needed to start the combustion reaction, and once the reaction has started it can be self-sustaining. The spark satisfies the activation energy needed. Then the heat released from the reaction causes a chain reaction igniting other fuel nearby. The reaction is then self sustaining. To occur a combustion reaction needs a fuel, an oxident and an ignition.

 

 

 

 

 

 

 

 

 

 

 

*Important Chemistry Points:

• An uncatalyzed combustion reaction occurs at high temperatures.

• Reaction is usually limited by the amount of fuel.

• Combustion engines utalize hydrocarbons other combustion reactions exist such as the burning of wood.

• Reaction heavily favors products so K is much greater than one.

• It is impossible however to get every bit of fuel to combust so K will be a real number (0 is not the denominator).

• Some materials combust better than others and hydrocarbons are used as a source of fuel in combustion engines.

• Different hydrocarbons are better for combustion engines, they release more heat that can be made into a greater amount of useful work.

• Delta G for the overall reaction is negative so the reaction is spontaneous.

• Spontenaity is measured in Kj/rxn and is represented by delta G.

 

Equation:

Delta G= DeltaH-DeltaS(Temperature in Kelvin)