Ethan is observing chemical and physical properties of a substance. He heats a substance and observes that the substance turn from a brown solid to a black powder. He refers to several chemistry...

Ethan is observing chemical and physical properties of a substance. He heats a substance and observes that the substance turn from a brown solid to a black powder. He refers to several chemistry journals that claim this represents a chemical reaction. From his observations and research he concludes that the substance goes through a chemical change when heated. How can Ethan best defend his conclusion?

Expert Answers
gsenviro eNotes educator| Certified Educator

Chemical and physical properties of a substance are related to chemical and physical changes, respectively. For example, melting point is a physical property and melting is the related physical change.

A chemical change takes place when the chemical composition of the substance changes. It can be represented with the help of a chemical reaction. For example, during cellular respiration, glucose is broken down into water, carbon dioxide and energy molecules (ATP). This chemical reaction can be written as:

`C_6H_12O_6 + 6O_2 -> 6CO_2 + 6H_2O +ATP`

Chemical changes are, thus, accompanied by the formation of new compounds.

Physical changes do not cause any change in the chemical composition of a substance. In other words, no new substance is formed; only the state of the matter may change. However, at the molecular level, the same molecules are present before and after a physical change. For example, when we melt a piece of iron, it coverts to liquid iron; however, in both cases, the substance is still iron.

Ethan can best defend his conclusion by demonstrating that the chemical composition of the substance has changed during heating. In other words, he needs to show that the substance contains different molecules than it did before the heating. This would be his best defense for claiming a chemical reaction (or change).

Hope this helps. 

dcbiostat eNotes educator| Certified Educator

Signs that a chemical change has occurred include color changes, bubbles, and the formation of a precipitate.

Chemical changes are changes that result in the formation of a new substance. In other words, the composition of a substance changes when the substance undergoes a chemical change. Chemical reactions are chemical changes.

Chemical weathering causes rock to undergo a chemical change. During chemical weathering, chemical reactions break down the bonds that hold the rock apart, causing the rock to fall apart into smaller and smaller pieces. Agents of chemical weathering include acid rain, oxidation, hydrolysis, carbonation, or dissolution.

Thus, the fact that a new substance was created and a color change occurred indicate that the substance Ethan was observing went through a chemical change.

 

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