Q1) State whether these processes are endothermic or exothermic. Give a reason for each.

a) Burning a charcoal briquette

b) Water evaporating from your skin

c) Ice melting

1a) Exothermic. A charcoal briquette releases heat as it burns.

1b) Endothermic. Water absorbs the heat needed for evaporation from your skin and hence your skin feels cooler.

1c) Endothermic. Ice absorbs the necessary heat to melt from the surrounding environment.

Q2) Chemical explosions are very exothermic reactions. Describe the relative bond strengths in the reactants and products that would make for a good explosion.

2) The products’s bond energies are larger that those of the reactants. This will lead to a negative net energy change resulting a large exothermic reaction. Thereby making it suitable for a good explosion.

Q3) How might you explain the differences between temperature and heat to a friend? Use some practical, everyday examples.

3) I would explain to him by saying the following:

Would you rather spill a drop of hot soup on yourself or a whole bowl of it at the same temperature. Though the drop and the bowl of hot soup are of the same temperature, you will get a bigger burn from the greater volume of the soup because it is of higher heat content. Heat is a form of energy. It always flows from a point of higher temperature to a point of lower temperature. On the other hand, temperature is a unit of measurement that indicates the direction heat will flow.

Q4) A premium gasoline available at most stations has an octane rating of 98. What does that tell you about:

a) the knocking characteristics of this gasoline?

b) whether the fuel contains oxygenates

4a) Gasoline with 92 as its octane rating shares the same knocking characteristics as a mixture that is made up of 92% isooctane and 8% heptane. Therefore, it is resistant to knocking.

4b) The octane rating does not provides any information if the fuel contains any oxygenates. Other labels around the pump should show this piece of information instead.