1a. Exothermic. When charcoal burns, heat is released, hence its exothermic.

1b. Endothermic. When water molecules evaporate to form water vapour, water vapour contains more energy. Furthermore, the skin feels cool as temperature decreases when water evaporates, hence it is endothermic.

1c. Endothermic. Heat is absorbed when ice melts, forming water molecules in liquid state which contains higher energy.

2. For a good explosion, a large amount of energy should be released. Hence the reaction should be very exothermic. Therefore the energy taken to break the bonds from the reactants should be much smaller than the energy released to form the bonds from the products, hence there will be a large net energy released. Thus, bond strength in the reactants should be low and the bond strength from the products should be strong.

3. Heat is the energy that flows from the hotter object to the cooler object. Temperature determines the flow of the energy as a hotter object will have a higher temperature and vice versa. In winter when your hands are cold, heat flows from the heat pack to your cold hands, this is because the temperature of the heat pack is higher than the temperature of your cold hands.

4a. An octane rating of 98 has a knocking characteristics of 98% isooctane and 2% heptane.

4b. No oxygenates are not present as if they are, the octane rating will be equal or higher than 109.