Video Transcript
Paraffin wax is a soft solid used in candles and lubricants. Listed in the table are three processes that are observed when paraffin is heated and the temperatures at which these changes take place. The process of melting takes place at a temperature of 60 degrees Celsius, combustion takes place at 245 degrees Celsius, and boiling takes place at 320 degrees Celsius. Identify the exothermic processes listed in the table.
This question is asking us to determine which of the three processes listed in the table are exothermic. A process that is exothermic releases some form of energy into its surroundings. A process that does the opposite by absorbing energy from its surroundings is an endothermic process. Let’s start by defining what occurs in these three processes so we can identify which processes release energy into the surroundings.
The process of melting is the conversion of a solid to a liquid. So, when a solid piece of paraffin is heated to 60 degrees Celsius, it changes from a solid state to a liquid state. This process requires energy to be added or in other words absorbed by the paraffin in the form of heat. And thus, this process is endothermic.
Combustion is the reaction of a substance with oxygen. It is generally very rapid and involves the conversion of chemical energy to heat. It is also known as burning. When paraffin reacts with oxygen and undergoes combustion at 245 degrees Celsius, it releases energy in the form of heat in addition to producing carbon dioxide and water vapor. Because this process releases energy to its surroundings, combustion is exothermic.
The final process provided, boiling, is the conversion of a substance from a liquid to a gas. When liquid paraffin is heated to 320 degrees Celsius, it changes from a liquid state to a gaseous state. This process required energy to be added in the form of heat, or in other words energy was absorbed by the paraffin. Boiling is an endothermic process.
Thus, we have identified the exothermic process listed in the table, which is combustion.
