Gasoline does not spontaneously combust inside the gas tank of a car due to several key factors, primarily involving thermodynamics and chemical kinetics.
Firstly, while the combustion of gasoline is thermodynamically favorable—meaning it is energetically beneficial for the reaction to occur—this does not guarantee that the reaction will occur spontaneously under standard conditions. A reaction may be thermodynamically favorable yet requires a specific set of conditions to initiate, which includes the presence of an appropriate ignition source.
In the case of gasoline in a gas tank, it is stored in a liquid state and is not exposed to a sufficient amount of heat or an ignition source to trigger combustion. The activation energy required to initiate combustion is not met in standard conditions; without a spark or extreme heat, the gasoline cannot ignite.
Moreover, gasoline vapors are volatile, and while they can mix with air, they need to reach a specific concentration with an adequate ratio of air to fuel combined with a source of heat to ignite. The gas tank is designed to contain gasoline safely, preventing any accidental ignition through factors like spark generation or overheating.
In summary, while the combustion of gasoline is a favorable reaction thermodynamically, specific conditions, including sufficient activation energy and the right mixture of fuel and air, must be met for the reaction to occur. This is why gasoline remains stable and does not spontaneously combust in the tank of your car.