Application Exercise 3

1a) Exothermic. Combustion gives out heat.

b) Endothermic. Liquid water absorbs heat to become vapour and have more kinetic energy to evaporate away.

c) Endothermic. Solid absorbs heat to become liquid.

2) enthalpy-change

To give an exothermic reaction, bond strengths in products have to be higher than those in reactants. To give a highly exothermic reaction, bond strengths in products should be much higher than those of reactants. Highly negative value should be obtained.

3) Temperature is a measure of the average speed of the molecular motion, and it determines the direction of heat flow. Heat is the energy that flows from a hotter to a colder object. Heat is a consequences of motion at the molecular level.

A glass of boiling water has a high temperature, therefore it is hot. One can feel the heat from the glass due to the transfer of energy from the hot water to your hand. This transfer of energy is referred to as heat.

4a) An octane rating of 98 means that the mixture contains 98% isooctane and 2% n-heptane. It burns smoothly and is more resistant to knocking than octane with lower rating.

b) The octane rating does not show us whether the fuel oxygenates.

 

Author: Thomas Chen

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