Chapter 6 combustion

Combustion

Chemical reaction between oxygen and another substance.

Combustion reactions are decomposition reactions in which oxygen oxidizes a combustible to produce __________ and ______

The product and heat

Combustible (fuels)

Material that can be oxidized with ignition source.

Combustibles can be in the form of a solid, liquid, or gas

true

Combustion reactions are redox and endothermic reactions

false; they are redox and exothermic

What requirements are necessary to initiate and sustain combustion?

a combustible/fuel, oxidant, source of activation energy, sufficient contact time for the energy to activate the reaction

Detonation

Combustion that propagates faster than sound (>343 m/s e.g. explosion)

Deflagration

Combustion that propagates slower than sound (

Flashpoint

the lowest temperature at which a substance generates a sufficient amount of vapor to form a vapor/air mixture that can be ignited

Fire point

the lowest temperature at which a substance generates a sufficient amount of vapor to form a vapor/air mixture that will sustain combustion once ignited

Ignition temperature

Minimum temperature for liquid ignition.

Ignition temperature can be reduced by the use of internal sources such as

a spark or flame

Autoignition

Ignition without external ignition source.

Minimum Ignition Energy

Energy required for autoignition of a mixture.

Stoichiometric Equivalence (STE)

The point at which a fuel and an oxidant create a 0 oxygen balance

• Exact molar ratio where reactants combine in a chemical reaction without any excess of one reactant

Fuel to air ratio

Comparison of fuel quantity to air in combustion.

Fuel to air ratio equation

FAR = (mass of fuel) / (mass of air).

Fuel to air ratio helps to determine

flammability

Lean mixture

Oxidant concentration exceeds stoichiometric ratio.

• < 1 (overoxidized)

Rich mixture

Fuel concentration exceeds stoichiometric ratio.

Vapor pressure

Pressure exerted by vapor in a closed container due to vapor phase of the liquid.

As temperature and volatility increases, vapor pressure ___________

increases

Volatility

Tendency of a substance to vaporize.

Activation energy

Energy needed to initiate a chemical reaction.

Oxidation

Loss of electrons during a chemical reaction.

Oxidation is indicated by an ________ in oxidation number

increase

Reduction

Gain of electrons during a chemical reaction.

reduction is indicated by _________ in oxidation number

decrease