Tag Archives: application

AE 3: Energy from Combustion

QUESTION 1

a. A charcoal briquette burns

> Exothermic as heat will be released by the burning charcoal briquette.

b. Water evaporates from your skin

> Endothermic as heat will be absorbed during evaporation.

c. Ice melts

> Endothermic as heat will be absorbed during melting.

 

QUESTION 2

Bond breaking in reactants will be an endothermic process whereas bond formation in products will be an exothermic process.

The energy absorbed during bond breaking (reactant) must be low while the energy released during bond formation (product) must be high to result in a negative net energy change, which also refers to an exothermic reaction.

For a good explosion, bond strength of reactants should be weak so lesser energy will be required to break bonds while bond strength of products should be strong so as to release more energy. This will result in a greater negative net energy change and hence a very exothermic reaction (good explosion).

 

QUESTION 3

Temperature is a form of measurement whereas heat is a form of energy.

For eg, comparing between a drop of hot water and a cup of hot water. Both are of the same temperature but it will be more tolerable to touch a drop of hot water as compared to a cup of hot water due to the difference in heat content.

 

QUESTION 4

a. Gasoline with an octane rating of 98 has the same knocking characteristic of 98% isooctane and 2% heptane. It has high octane rating hence it will be resistant to knocking.

b. The octane number of the gasoline will not tell us if it contains oxygenates but fuel with oxygenates do have higher octane ratings. Some common oxygenated fuel additives have octane ratings of over 100.