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.
- Exothermic. Heat is released.
- Endothermic. Heat is absorbed to break bonds.
- 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.
- Heat is the total energy of the molecular motion in a substance.
- Temperature is the measure of the average energy of molecular motion of a substance.
- Heat is a type of energy but temperature is not energy.
- 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?
- It has a knocking characteristics of 98% isooctane and 2% heptane.
- 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.