CM8001

a. Exothermic, burning gives off heat energy.
b. Endothermic, during evaporation water takes in heat energy and skin feels cooler.
c. Endothermic, during melting ice absorbs heat energy though there’s no change in temperature.

Initial reactant bond strength has to be weak while product bond strength has to be strong to lead to an exothermic reaction. Reactant bond strength is relatively much weaker than product bond strength so that it can be highly exothermic enough to be explosive. Gases are more reactive than solids or liquids due to their weaker bonds.

Heat: total energy (kinetic + potential) possessed by molecules in a piece of matter, measured in joules, and has the ability to do work.
Temperature: not energy, measured in Kelvin, can only be used to measure the hotness or coldness of something.
Eg, during melting, there is no change in temperature, but there is transfer of heat from the surroundings to the ice.

a. It has high anti-knocking characteristics. Higher rating means better for the engine.
b. We do not know. Rating simply corresponds to knocking characteristics and is used as a form of comparison between types of gasoline.