Question 1
- Exothermic. It is a combustion reaction.
- Endothermic. Liquid water molecules absorb energy to overcome the intermolecular forces between h20 molecules to become gaseous vapour.
- Endothermic. When solid ice melts into water, energy is absorbed, increasing kinetic energy of its molecules, explaining its liquid state.
Question 2
To make a good explosion, the total amount of energy in reactants should be much, much greater than the final total amount of energy in its products, so that the enthalpy change (-ΔH/ energy released) will be huge.
Therefore, bond strength in reactants has to be very strong as compared to bond strength in products (weak).
Question 3
Temperature is an objective measurement of the amount of heat energy present in a body, which is represented using units like the Kelvin scale (for absolute temperature) and Celcius/Fahrenheit.
eg. “It is hot and sunny outside. The weather forecast says it would be 37 degrees Celcius.”
Heat refers to the total energy of all molecular motion inside an object. The hotter an object, the more rapid the molecules move inside it. Heat is also defined as the transfer of kinetic energy from one body to another.
eg. “Put the pack of ice next to the frozen food we bought, not next to the hot food, or else the ice will melt faster from the heat.”
eg. Heating a beaker of water over a bunsen burner with a thermometer.
eg. Chemical energy from burning of gas is converted to thermal energy to heat the water, which results in the bubbling of water and a rise in surrounding air temperature. The amount of heat energy converted is measured by the thermometer in the water.
Heat can be physically felt, temperature cannot. Heat energy depends on the size and type of object on how it conducts heat; temperature not dependent.
eg. A metal plate and a book in the same set-up, both are at same temperatures, however the heat we perceive when we touch them are different.
Question 4
(a) Octane rating of 98: knocking characteristic of 98% isooctane & 2% heptane. The higher the octane number, the more compression the fuel can withstand before igniting. It is a measure of the ability of gasoline to burn smoothly without knocking (resistance).
(b) Octane rating provides no information about the presence of oxygenates.