Tag Archives: Endothermic

CM8001 – Application Exercise 3 (8/02/2017)

  1. From personal experience, state whether these processes are endothermic or exothermic. Give a reason for each.
    a. A charcoal briquette burns
    answer: Exothermic. When charcoal briquette is ignited, it gives out heat.b. Water evaporates from your skin
    answer:
    Exothermic. Water takes in heat from my skin in order to evaporate.c. Ice melts
    answer:
    Exothermic. Ice takes in heat from the surrounding in order to melt.
  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:
    Enthalpy change = (sum of bond energy broken, positive value) – (sum of bond energy formed, negative value)
    Explosion is an exothermic reaction with a negative enthalpy. A good explosion needs to have a large negative enthalpy.
    Hence, the bond strength of reactants has to be smaller than that of the products.
  3. How might you explain the difference between temperature and heat to a friend? Use some practical, everyday examples.
    answer:
    a. Heat is the total energy of molecular motion in a substance while temperature is a measure of the average energy of molecular motion in a substance.
    b. Heat is energy while temperature is not.
    c. Heat depends on the number and speed of particle while temperature does not.
    Examples: Temperature of a small cup of water might be the same with water in a large tub. However the large tub of water has more heat because it has more water, thus has more total thermal energy.
  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 the gasoline?
    answer:
    The gasoline has the knocking characteristics similar to the combination of 98% of iso-octane and 2% heptane.b. whether the fuel contains oxygenates?
    answer:
    The presence of oxygenated cannot be determined simply by the octane rating as the octane rating only functions to describe the characteristics of the gasoline. An octane rating of 98 can be derived from a mixture of oxygenates such as MTBE, Methanol or ethanol with octane, or heptane and it can also be derived from a mixture of isooctane with octane or heptane which are both not oxygenates.