The world is constantly changing.
A course in History would make you realize how societies have changed. Empires come and go as countries fight wars. The environment changes as human development occurs. Earth and Life Science, on the other hand, will make you realize that the Earth underwent change, is changing, and will change in the years coming. From a planet of hot gases and violent conditions to the home where we live in now today, Earth has come a long way. Even Biology would talk about change. Life forms have evolved in a process called natural selection. As time passed by, organisms have passed on favorable and adaptive traits to their offspring.
This holds true for Chemistry. Chemical changes happen, and it is all because of energy. We can’t see energy, but we can sense and measure its effect when it has been transferred between a system and its surroundings. This is the same energy that is present when we form or break bonds between molecules.
A chemical reaction that gives off light, heat or sound is called an exothermic reaction. In this reaction, heat is lost to the environment, and the temperature of the surroundings rises. An example is the formation of bonds, which gives off heat. It is signified by a negative enthalpy, the total heat content of a system. On the other hand, a reaction that takes heat energy from its surroundings is called an endothermic reaction. It causes the temperature of the environment to drop. Energy is supplied when we break bonds. It is denoted by a positive enthalpy.
As part of our course in General Chemistry II, we conducted an activity on Chemical Energetics, the study of chemical changes caused by energy. We were given the procedures, and the challenge is to identify each reaction as endothermic or exothermic. The following are the reactions we did and their corresponding energy level diagrams:
dilute hydrochloric acid and sodium hydroxide
The initial temperature reading is 19 degrees C while the final is 20 degrees C. The reaction is exothermic.
zinc dust and dilute hydrochloric acid
The initial temperature reading is 21 degrees C while the final is 22 degrees C. The reaction is exothermic.
barium chloride and water
The initial temperature reading is 25 degrees C while the final is 22.5 degrees C. The reaction is endothermic.
ammonium chloride and water
The initial temperature reading is 25 degrees C while the final is 24.5 degrees C. The reaction is endothermic.
sodium hydroxide and water
The initial temperature reading is 25.5 degrees C while the final is 26.5 degrees C. The reaction is exothermic.
magnesium sulfate and water
The initial temperature reading is 14 degrees C while the final is 15 degrees C. The reaction is exothermic.
potassium dichromate and ethanol
The initial temperature reading is 20 degrees C while the final is 23.5 degrees C. The reaction is exothermic.
anhydrous copper sulfate and water
The initial temperature reading is 34.5 degrees C while the final is 32.5 degrees C. The reaction is endothermic.
When the temperature from the initial reading to the final reading increases, the reaction is exothermic. The increase in temperature is caused by the heat released to the environment. The products have less energy than the reactants, so ∆H is negative. When the temperature from the initial reading to the final reading decreases, the reaction is endothermic. The decrease in temperature is caused by the heat absorbed from the environment. The products have more energy than the reactants, so ∆H is positive.
This is our last laboratory activity of General Chemistry II, so it was memorable. Through the months, I’ve seen how my laboratory peers have grown from clueless beginners to resourceful scientists. They became so independent that they can easily identify which materials to use given just the procedures. Collaboration also played an important part in the completion of lab activities. Everyone performed their roles in order to contribute to the success of their respective groups. In addition, friendly competitions happened during discussions. Every answer was a pressure and every point mattered.
I learned to be curious with whatever is happening inside the laboratory. I may not be able to help in lab procedures, but it became my habit to question something bizarre and try to answer it. It is not enough to identify the unusual. We must try to find out what causes it. The beauty of chemistry is trying to find out the answer to something by actually trying it out many times. Finding the answer after several trial-and-errors makes it all the more worth it.
When we encounter lab works in the future, we won’t be lost since we already understand the functions of lab tools and techniques. We would look back and reflect on our days in General Chemistry. Times may change, but the memories are there forever.