Is A Rusting Nail A Chemical Change
10.4: Physical and Chemical Changes
- Page ID
- 58840
Learning Outcomes
- Distinguish between physical and chemical changes.
- Requite examples of physical and chemical changes.
Concrete Changes
As an water ice cube melts, its shape changes as it acquires the ability to flow. However, its composition does not modify. Melting is an example of a concrete modify. A physical change is a modify to a sample of matter in which some properties of the material modify, but the identity of the matter does non. Physical changes tin can farther be classified as reversible or irreversible. The melted ice cube may be refrozen, and so melting is a reversible physical change. Concrete changes that involve a change of state are all reversible. Other changes of state include vaporization (liquid to gas), freezing (liquid to solid), and condensation (gas to liquid). Dissolving is also a reversible physical modify. When salt is dissolved into water, the salt is said to have entered the aqueous country. The common salt may be regained past humid off the water, leaving the salt backside.
When a piece of woods is ground into sawdust, that change is irreversible since the sawdust could not be reconstituted into the same piece of wood that it was before. Cutting the grass or pulverizing a stone would be other irreversible concrete changes. Firewood also represents an irreversible physical change since the pieces cannot be put dorsum together to grade the tree.
Chemical Changes
When exposed to air, an object made of iron will somewhen brainstorm to rust (see figure below).
As the rust forms on the surface of the iron, information technology flakes off to expose more iron, which will continue to rust. Rust is clearly a substance that is different from atomic number 26. Rusting is an example of a chemical change.
A chemic property describes the ability of a substance to undergo a specific chemic change. A chemical property of iron is that information technology is capable of combining with oxygen to form iron oxide, the chemic name of rust. A more full general term for rusting and other similar processes is corrosion. Other terms that are commonly used in descriptions of chemic changes are burn down, rot, explode, and ferment. Chemical properties are very useful as a way of identifying substances. However, unlike physical properties, chemic properties tin can simply be observed equally the substance is in the process of being inverse into a different substance.
A chemical change is also called a chemical reaction. A chemical reaction is a process that occurs when one or more substances are changed into one or more new substances. Zinc \(\left( \ce{Zn} \right)\) is a silvery-gray chemical element that can be footing into a powder. If zinc is mixed at room temperature with powdered sulfur \(\left( \ce{Southward} \right)\), a bright yellow element, the effect will simply be a mixture of zinc and sulfur. No chemical reaction occurs. Withal, if energy is provided to the mixture in the form of heat, the zinc will chemically react with the sulfur to course the compound zinc sulfide \(\left( \ce{ZnS} \right)\). Pictured below are the substances involved in this reaction.
The reaction between zinc and sulfur tin be depicted in something called a chemic equation. In words, we could write the reaction every bit:
\[\text{zinc} + \text{sulfur} \rightarrow \text{zinc sulfide}\]
A more convenient manner to express a chemical reaction is to utilize the symbols and formulas of the substances involved:
\[\ce{Zn} + \ce{Southward} \rightarrow \ce{ZnS}\]
The substance(s) to the left of the arrow in a chemical equation are called reactants. A reactant is a substance that is present at the first of a chemical reaction. The substance(s) to the correct of the arrow are called products. A product is a substance that is present at the finish of a chemical reaction. In the equation in a higher place, zinc and sulfur are the reactants that chemically combine to course zinc sulfide as a product.
Recognizing Chemic Reactions
How tin can you tell if a chemical reaction is taking place? Sure visual clues betoken that a chemical reaction is likely (but not necessarily) occurring, including the following examples:
- A change of colour occurs during the reaction.
- A gas is produced during the reaction.
- A solid production, called a precipitate, is produced in the reaction.
- A visible transfer of free energy occurs in the form of low-cal as a upshot of the reaction.
When zinc reacts with hydrochloric acid, the reaction bubbles vigorously every bit hydrogen gas is produced (encounter figure below). The production of a gas is also an indication that a chemical reaction may exist occurring.
When a colorless solution of pb (II) nitrate is added to a colorless solution of potassium iodide, a xanthous solid called a precipitate is instantly produced (run into figure below). A precipitate is a solid product that forms from a reaction and settles out of a liquid mixture. The germination of a precipitate may also indicate the occurrence of a chemical reaction.
\[\ce{Atomic number 82(NO_3)_2} \left( aq \correct) + two \ce{KI} \left( aq \correct) \rightarrow \ce{PbI_2} \left( s \right) + two \ce{KNO_3} \left( aq \right)\]
Contributors and Attributions
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Allison Soult, Ph.D. (Department of Chemistry, University of Kentucky)
Source: https://chem.libretexts.org/Courses/University_of_Kentucky/UK:_CHE_103_-_Chemistry_for_Allied_Health_%28Soult%29/Chapters/Chapter_10:_Nuclear_and_Chemical_Reactions/10.4:_Physical_and_Chemical_Changes
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