 Welcome back MechanicalEI, did you know that combustion was a first controlled chemical reaction discard by humans in the form of campfires and bonfires? This makes us wonder, what is combustion? Before we jump in, check out the previous part of this series to learn about what the Atkinson and Praden cycles are. Now combustion or burning is a high temperature exothermic redox chemical reaction between a fuel which is the reductant and an oxidant usually atmospheric oxygen that produces oxidized often gaseous products in the mixture termed as smoke. Combustion in a fire produces a flame and the heat produced can make combustion self-sustaining. Combustion is often hot enough that light in the form of either glow or flame is produced. The standard enthalpy change of combustion of a compound is the enthalpy change which occurs when one mole of the compound is burnt completely in oxygen under standard conditions and with everything in its standard state. The enthalpy change of combustion will always have a negative value from the thermodynamic point of view because burning always releases heat. Hence, we first saw what combustion is and then went on to see what the enthalpy of combustion is.