Does Dissolving Salt In Water Change Temperature

Dissolving salt in water may be considered a chemical change or a physical change. — Dissolving common salt in h2o may be considered a chemical alter or a physical change. If you lot're forced to option a side, almost chemists say dissolving a covalent compound (similar sugar) is a physical modify, but dissolving an ionic chemical compound (similar common salt) is a chemical change.

Is dissolving table common salt (sodium chloride or NaCl) a chemical alter or a concrete alter? This is a common full general chemistry question. The problem is that the respond is disputed. Here are valid arguments for both answers.

Many chemists consider dissolving table salt (or any ionic solid) to be a chemical change. Dissolving sugar (or any covalent solid) is a physical change.

Why Dissolving Salt Is a Chemic Change

A chemical change involves a chemical reaction and the formation of new products. Dissolving salt in water may exist written equally a chemic reaction, where sodium chloride dissociates into Na⁺ ions and Cl^– ions in water.

NaCl(s) → Na⁺(aq) + Cl^–(aq)

When salt dissolves, the ionic bonds betwixt the atoms break. The reactant (sodium chloride or NaCl) differs from the products (sodium and chloride ions), so a chemical change occurs. The same reaction occurs when other ionic compounds dissolve in water. To generalize: Dissolving an ionic chemical compound is a chemical modify. In contrast, dissolving saccharide or another covalent chemical compound is a physical change considering chemical bonds are non broken and new products are not formed. If you dissolve carbohydrate in water, you get sugar molecules in h2o.

Why Dissolving Salt in Water Is a Physical Change

A physical change involves a change in a physical property, but not a modify in chemical composition. Examples include changes in states of matter or alterations to crystal construction.

Dissolving salt in water may be considered a physical change because no change occurs in the electron shells of the sodium and chlorine atoms and no chemic reaction occurs between sodium chloride and its solvent (water). In contrast, if you dissolve table salt in acetic acid (CH₃COOH), you get sodium ethanoate (CH₃COONa) and hydrochloric acid (HCl).

Sometimes the reason given for proverb dissolving table salt is a physical alter is that the procedure is reversible. If yous remove the water, you recover salt. The problem is that many chemical changes are reversible. For example, weak acids and weak bases typically participate in reversible reactions that eventually reach equilibrium. Mixing carbonic acid in water is an example:

H₂CO_{3 (l)} + H₂O_(l) ⇌ HCO₃ ⁻ _(aq) + H₃O⁺ _(aq).

Meanwhile, many physical changes are not reversible. For instance, you tin't put a sheet of paper dorsum together again after you lot shred it.

Teaching Considerations

On the one hand, discussing whether dissolving carbohydrate and salt are chemical or physical changes is a good way to go students thinking nearly changes in matter. Information technology's an opportunity to talk most how you know whether a chemical reaction has occurred. On the other hand, all of the signs of a chemic change (temperature change, color change, odor, bubbling, precipitate formation) occur with some concrete changes.

If a educatee is asked whether dissolving salt is a chemical change or a physical modify, some instructors consider it unfair to marker either answer incorrect, providing the student can explain the reply. Other teachers feel strongly about the answer. In this case, it's important to convey expectations to the form prior to homework or an exam.

Simply, what do you recall? Experience free to post a annotate.

References

Colina, John West., et al. (2004) General Chemistry (4th ed.). Prentice Hall. ISBN: 978-0131402836.
Zumdahl, Steven Due south.; Zumdahl, Susan A. (2000).Chemistry (5th ed.). Houghton Mifflin. ISBN: 0-395-98583-8.