1a. Charcoal briquette burning is an exothermic reaction. It produces heat, from personal experience.

1b. Endothermic reaction, as heat is absorbed for water molecules to gain energy and eventually gain sufficient energy to leave the water surface as a gas molecule, which is water vapour. Thats why we feel cool when we sweat.

1c. Endothermic reaction, it requires heat is absorbed for ice molecules to gain kinetic energy and eventually gain sufficient energy to become a water molecule.

2. The starting reactants have much more energy than the products. Exothermic reactions need only release energy to the surroundings by converting chemical potential energy into kinetic energy. Therefore, for a good explosive, the bonds of the reactant is much stronger that the product ones.

3. Heat is why you feel hot or cold, and temperature is just the measurement of the average kinetic energy of the molecules. The room feels warmer, due to the heat energy in the room – the temperature is 25 degrees celsius.

4a. The quality of the gasoline is higher, the higher the rating the lower the knocking. Less impurities inside. It has 98 percent of isooctane and 2 percent of heptane.

4b. higher rating means more oxygenates. so it has a relatively high percentage of oxygenates. Thus, more complete combustion, and less pollutants.