Question

Autoignition temperature is the highest temperature at which substance can burn.
A.True
B.False

Answer 1

Hint: Autoignition temperature is otherwise known as kindling point. Autoignition happens when no external ignition source is spontaneously ignited by a combination of gases or vapours and the autoignition temperature is achieved after exceeding a certain temperature.

Complete step by step answer:
Let us first understand what is an Autoignition temperature;
Autoignition temperature is the lowest temperature at which the substance starts combustion. To provide the activation energy needed for combustion, this temperature is necessary. When the pressure or oxygen concentration rises, the temperature at which a chemical ignites diminishes.
This is not an intrinsic property of the gases or vapours, but is the lowest temperature in a system where the rate of heat developed from the gases or vapours grows, resulting in ignition, above the rate of heat loss to the atmosphere.

So, From this definition itself it is clear that, the given statement is false.

Additional information:
For fuels in general, even at near-limiting concentrations, the autoignition temperature is not very sensitive to fuel concentration. The effect of catalytic surfaces on the autoignition temperature differs with the system. Any experiments suggest that in some systems, catalytic surfaces raise the temperature of autoignition.

Note: Pressure, vessel shape and length, surface activity, pollutants, flow rate, reaction rate, droplet and mist formation, gravity and reactant concentration are influenced by the autoignition temperature of a mixture of gases or vapours. In general, decreased pressure contributes to an increased temperature of autoignition, while increased vessel size contributes to a decreased temperature of autoignition.