CM8001

A. Exothermic: Combustion reactions are exothermic.

B. Endothermic: Conversion from a liquid state to gaseous state requires the compound to take in energy from the skin so as to break the strong hydrogen bonds between the molecules in the liquid state.

C. Endothermic: Ice absorbs environmental heat to overcome the strong intermolecular bonds to liquefy.

Exothermic reactions release energy during the reaction. Therefore, the energy of the products will be lower than that of the reactants.

A good explosion happens vert fast and almost instantaneously, therefore the bond strength in the reactant have to be as low as possible so that it can be broken fast during the reaction. On the other hand, bond strength of the products have to be high in order to form stable products.

Heat of an object is the total energy of all the molecular motion inside that object. Temperature, on the other hand, is a measure of the average heat or thermal energy of the molecules in a substance.
Hence, in other words, temperature is the scale or the unit of measurement for heat, just like centimetres is a unit of measure for length. Therefore, you can only feel “heat” and not “temperature”.

A. An octane rating of 98 refers to the amount of octane there is in the petrol. The higher the octane rating, the less likely knocking will occur, because octane burns slower since it has longer-chained hydrocarbon and is more resistant to igniting prematurely.

B. Adding oxygenates increases the concentration of octane in the fuel, so presumedly a premium gasoline with an octane rating of 98 will have a higher concentration of oxygenates contained in the petrol mix.