CM8002: AE3


a) A charcoal briquette burning is an exothermic reaction, as heat energy is released as it burns.

b) Water evaporating from our skin is an endothermic reaction, as water molecules absorb heat from the body to increase it’s kinetic energies. This explains why sweat cools the body down as it evaporates from our skin.

c) Ice melting is an endothermic reaction, since the melting of ice requires heat to increase the kinetic energies of the molecules.

2: Chemical Explosions are very exothermic reactions. Describe the relative bond strengths in the reactants and products that would make for a good explosion:

An indication that a large exothermic reaction would occur is when there is a negative net change in energy between the products and the reactants, which results from the bond energies in the products being larger than those belonging to the reactants.


3: Temperature determines the direction of heat flow. Heat is the energy that flows from a hotter to a colder object. Heat is a consequence of motion at molecular level while temperature is a measure of the average speed of that motion.
Example a cup of water and a pail of water with the same temperature. Since the pail of water contains more water and has more mass, more amount of heat energy is required to boil and increase its temperature compared to the cup of water.

4a: A higher octane rating means the fuel is more resistant to knocking.  This allows a high performance engine to run safely by preventing it from igniting the fuel before the spark plug ignites it.

4b: Fuel with octane rating of 98 contains oxygenates such as ethanol, that has higher heat of vaporization for fuel/air charge cooling, thus allowing the engine to have high efficiency.