Physical and Chemical Changes

In class, we performed four labs that were all very alike. The purpose of these labs were to show examples of physical and chemical changes. A physical change is when the appearance of a substance changes, but the chemical composition does not change. On the other hand, a chemical change is when the chemical composition changes.

The first lab was called “Observing a Candle.” This lab was very simple. We observed a candle before and after it was lit. During this lab, I noticed a physical and a chemical change. After our teacher lit the candle, the candle wax started to melt. Melting is the process in which a solid, in this case the candle, turns into a liquid. This change is a physical change because the appearance of the candle changed. The chemical change that occured in this lab was when the candle started to burn. This would be a chemical change because the chemical composition of the candle changed. The candle caught on fire because of the way the components of the candle reacted with the fire.

The next lab our class performed was called "Pouring a Gas." In this lab, we made carbon dioxide. To do this, we had to mix vinegar and baking soda together. Once the mixture started to fizz, I knew a chemical change occurred. The combining of vinegar and baking soda is a chemical change because the chemical composition of the two components changed. The way the vinegar and baking soda reacted with one another caused a new substance to be formed -- carbon dioxide. Before making the carbon dioxide, our teacher lit a candle. To perform this lab, we had to hold the fizzing carbon dioxide over the candle. When we did this, the fire went out. This because carbon dioxide does not support fire.

The next day, our class did a lab called "Marshmallow Fun." For this lab, we were given small marshmallow and a large marshmallow. After describing the characteristics of both, we took the small marshmallow and ripped it in half. By ripping it in half, we made physical change occur. This would be a physical change because the appearance of the marshmallow changed, but the chemical composition did not change. After ripping it in half, we were allowed to eat it! After we finished using the small marshmallow, we moved on to the large marshmallow. Our teacher lit the Bunsen burner and we put the large marshmallows on on kabob sticks. We roasted the marshmallows over the burner until part of it turned black. The change that occurred in the marshmallows after I burnt it is called a chemical change because the substance changed after interacting with a different substance. Afterwards, we ate the large marshmallow. The burnt part tasted bitter and was hard and brittle. The inside of the marshmallow, however, was soft, creamy, and sweet.

The last lab we performed was a lab with sugar cubes. At the start of the lab, we took a couple sugar cubes and crushed them. This would be a physical change because the substance did not change, just the way it looked changed. Then we took the crushed up sugar and put it in a cup of water. The sugar dissolved immediately. At first, I was confused on whether this is a physical change or a chemical change. I then learned that it was a physical change because a new substance wasn't formed. The form of the sugar changed -- you could still separated the sugar from the water. Then, we put two sugar cubes in a test tube and put it over the Bunsen burner. The sugar went through different stages very fast. It melted, then became caramel, and then burnt all the way through. This would be a chemical change because it describes the way the sugar reacted with the heat. At the end of the lab, I tasted the burnt sugar. It was very bitter and very disgusting.

You can find physical and chemical changes all around you. When it is cold outside and you want to get cozy, you light the fireplace. That would be a chemical change. Another time you see a chemical change occur without even knowing is when you bake. The way the ingredient react with each other creates a whole new substance. In addition, physical changes take place all around you. For example, when comb your hair, you are making a physical change. Your hair is not changing, just the way it looks changes. Furthermore, you create physical changes when you eat. The crushing of the food in your mouth with your teeth is a physical change.

All in all, physical and chemical changes are all around us. You don't just see them in a chemistry lab. I also learned so much more about physical and chemical changes through the labs I completed. I can now tell the difference between the two and give example of both. Additionally, it was intriguing to see physical and chemical changes take place first hand.

Image Sources:

Candle

Marshmallow

Sugar