FUELS AND COMBUSTION (NOTES) HALF CHAPTER

Endothermic reactions – Reactions that occur due to the absorption of energy are called ER as heat flows in

Exothermic reactions- Reactions that occur due to release of energy are said to be ER as heat flows out

COMBUSTION The process of burning of a fuel by oxidation in presence of oxygen present in

the air is called combustion Mg ribbon burns to form MgO Charcoal or coal burns in presence of O2 n evolves CO2 along with heat n

light

1. PRESENCE OF COMBUSTIBLE SUBSTANCEa. Combustible sub are those sub which can catch fire easilyb. E.g.- clothes paper wood fuels etcc. Fire can’t be started if C sub is absentd. A C sub will only burn n not support pro of burninge. E.g. – H only burns n not support

2. PRESENCE OF O2 IN ADEQUATE AMMOUNTa. Sub can only burn in presence of O2b. Also called supporter of Cc. Insufficient supply- Incomplete Cd. LESS HEAT N LIGHTe. Carbon complete- CO2f. Carbon incomplete-CO

3. ATTAINMENT OF IGNITION TEMPa. Min temp to which a C sub has to be heated such that it starts burningb. KINDLING TEMP/IGNITION POINTc. Below this even a combustible sub along with O2 fire won’t start

White phosphorus 35 C Match contains red phosphorus along with other chemicals on striking friction

is created. Generates enough heat to light match n make chemicals catch fire Wood of diff variety Water used to ex fire cause reduces temp of the sub that has caught fire

below ignition temp. water vapour surrounds sub n cuts off o2 supply Oil catch fire-not pour water cause ignition temp of oil high also oil floats on

water n doesn’t mix so oil ll spread d fire To initiate wood/coal fire – dip a piece of cloth in kerosene n burn d cloth.

Place burning cloth on heap of wood / coal. This is cause ignition temp of wood/coal very high cant be attained by normal match

When a person’s clothes catch fire the person is covered with blanket temp of burning sub is reduced plus it cuts off o2 supply

Coal burnt in a closed room-undergoes incomplete C produce CO result in suffocating n even death

Chulha air is blown around pro o2 burn easy Blue flame C. yellow-in C Respiration pro of breathing n using o2 for various chemical n bio actions to

provide energy. It is released by breakdown of complex food molecules into simpler molecules in the presence of o2 inhaled so it is also C

INFLAMABLE SUB The sub whose ig temp is extremely low n whih can catch fire easily are called IS. E.G kerosene LPG CNG

TYPES OF COMBUSTION 1. RAPID C- Form of C in which large amount of heat n light r released in a very

short interval of time2. SLOW C-It is a type of C which takes place at low temp3. SPONTANEOUS C- It is a type of C which occurs without external source of

ig

The sudden evolution of large volume of gases creates excess pressure which produces a very loud noise this is called EXPLOSION.As temp rises above 55 c self-sustaining chemical fire ignites which doesn’t need o2 hence crops are dried before storage 2 prevents SC.SC of coal dust due to aerial oxidation in soft coal in small size is wetted to suppress atmospheric oxidation.

3 MOST IMP THINGS TO INITIATE A FIREA. AIRB. FUEL C. HEAT

Fire control consists of depriving a fire from either or all of these Standard method is to spray water on burning sub 2 remove heat Fire brigades pour water from hose pipes to extinguish fire Another method – smother fire with CO2 Being heavier than o2 acts as a blanket n covers fire thereby cutting off d o2

supply Co2 best to ex fire by inflammable sub n electrical app Doesn’t destroy electrical app