Question 1:

From personal experience, state whether these processes are endothermic or exothermic. Give a reason for each.

a) A charcoal briquette burns

This is a combustion reaction, heat is released during combustion, thus, this is an exothermic reaction.

b) Water evaporates from your skin

When water evaporates from your skin, you experience a cool sensation, the temperature drops because energy has been absorbed.  Water molecules must absorb heat from the surroundings to increase their kinetic energy.  Thus, this is an endothermic reaction.

c) Ice melts

Ice melting is an endothermic reaction, the melting process requires the absorption of heat from the surroundings.

Question 2:

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

The bond strengths in the reactant should be much lower than the bond strengths in the products for a good explosion. This is because if the bonds in the reactants are weaker, it need lesser energy to break the bond. While at the same time, if the bonds in the products are stronger, it can release more energy to create the bond. Explosion is a violent change of potential energy to work. For a good explosion more energy is needed.

Question 3:

How might you explain the difference between temperature and heat to a friend? Use some practical, everyday examples?

Heat is energy. It can be referred to the total energy possessed by the molecules in a substance. The faster the molecules or atoms in a substance are moving, there would be more heat energy, and hence the object is hot. On the other hand, if the particles in a substance are moving slowly, there would be less heat energy and hence the object is cold. Heat is transferred from a hotter to cooler systems that are in contact.

Temperature is not energy. It is the measure of average energy of molecules in a substance. Temperature is used to measure the degree of heat.

The more the heat, the higher the temperature and vice versa.

Examples:

1. A cup of fresh coffee is hot because the water particles are moving fast, giving the coffee heat energy, resulting in high temperature.
2. Ice added to a glass of water. Water with a higher temperature (water molecules are moving faster as compared to the molecules in ice) causes the ice to melt due to its heat energy generated.

Question 4:

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?

This gasoline can withstand more compression before igniting.

b) Whether the fuel contains oxygenates?

Oxygenates might have been added into the fuel to increase its octane rating.