Question 1. From personal experience, state whether these processes are endothermic or exothermic. Give a reason for each.

• A charcoal briquette burns.
• Water evaporates from your skin.
• Ice melts.

Answer:

1. Exothermic. Heat is released.
2. Endothermic. Heat is absorbed to break bonds.
3. Endothermic. Heat is absorbed to break the bonds.

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.

Answer: The relative bond strengths of the products are greater than that in the reactants, resulting in a very large exothermic reaction.

Question 3. How might you explain the difference between temperature and heat to a friend? Use some practical, everyday examples.

Answer:

1. Heat is the total energy of the molecular motion in a substance.
2. Temperature is the measure of the average energy of molecular motion of a substance.
3. Heat is a type of energy but temperature is not energy.
4. Heat cannot be directly measured with a device; temperature can be measured directly using devices such as thermometer.

For example, the hotness felt from a boiling kettle is the energy, and the degree of hotness can be measured using a thermometer.

Question 4. A premium gasoline available at most stations has an octane rating of 98. What does that tell you about:

• The knocking characteristics of this gasoline?
• Whether the fuel contains oxygenates?

Answer:

1. It has a knocking characteristics of 98% isooctane and 2% heptane.
2. No. Fuels that contains oxygenates would have octane rating over 100. Since the fuel has an octane rating of 98, it does not contain oxygenates.