CM8001

a. Exothermic. A charcoal briquette releases heat as it burns due the bond formation.
b.Endothermic. Water absorbs the heat necessary to break the hydrogen bonding for evaporation from your skin, and thus, the skin feels cooler.
c. Endothermic. Ice absorbs the necessary heat from the environment to break the hydrogen bonds in order to melt into a liquid.

For a good explosion to occur, it has to be an exothermic reaction. Hence, the bond strength (bond energy) of the products has to be much higher than that of the reactants. Thus, this would result in a higher negative net energy change, leading to a good explosion.

For example in methane explosion:
CH4 + 2O2 -> CO2 + 2H2O
Given that C-H bond: 416 kJ/mol; O=O bond: 498 kJ/mol; C=O bond: 803 kJ/mol; O-H bond: 467 kJ/mol
Hence, the bond formation energy is much larger than the bond-breaking energy.

Moreover, for a good explosion, the product would be in a gas state.

Temperature is not a form of energy as it is a measure of the average speed of the direction of heat flow. Whereas, heat is a form of energy that transfers from hotter region to colder region.

For instance, a cup of water has the same temperature as a tub of water. However, the tub of water contains more heat than the cup of water due to the larger volume of water in a tub, which resulted in the higher heat content of the tub of water.

Octane rating is the measure of the ability of gasoline to burn smoothly without knocking.

a. The octane rating of 98 means that the premium gasoline has a knocking characteristic of 98% isooctane and 2% heptane.

b. The presence of oxygenates in the premium gasoline cannot be determined from the octane rating. Other labels on the packaging should reveal this information.