CM8001

a) Exothermic. A charcoal briquette release heat as it burns, combustion.
b) Endothermic. Evaporation is an endothermic change because water gain energy as they changes from liquid to gas state.
c) Endothermic. Melting process needs heat to proceed.

The reactant has way higher energy than the product. At the end of the reaction, it gives off a lot of energy and that cause the explosion. The higher the relative bond strength the bigger the explosion.

Temperature determine the direction of the heat flow while heat is the energy that flows from a hotter to a colder objects.
Example: Temperature of a small cup of water might be the same as the temperature of a large tub of water, but the tub of water has more heat because it has more water and thus more total thermal energy.

a) Gasoline with an octane rating of 98 has the same knocking characteristic as a mixture composed of 98% isooctane and 2% heptane. In essence, this is a blend that is resistant to knocking.
Knocking: explosion caused by premature burning in the combustion chamber.

b) The octane rating does not give any additional information about whether or not the fuel contains oxygenates. Other labels around the pump should reveal this information.