Which forms of evidence show that a chemical reaction has taken place?

Answer 1

new substances are formed with new properties.

when a object changes its form

A chemical reaction has occurred when the chemical identity of a the reactants is different from that of the products. The evidence for this could be obvious or very subtle. For instance, if a colorless gas reacts to form another colorless gas, there would be no visible sign of the reaction. However, often a chemical reaction will cause a change in color or the formation of a solid. The tools you might use to determine if a reaction has taken place depends a great deal on what the suspected reaction is (or what the products formed would be). The most common method is to use analytical chemical technique to verify the presence of the product molecules, or the disappearance of reactant molecules.

Note that there are many physical changes that can be confused with chemical changes. For instance, boiling water or freezing water results in many changes in the properties of water, but those are physical changes, not chemical ones. But whether water is liquid, solid or a gas, it is still water, and that is why it is a physical rather than chemical change.

See the Related Questions for more information about the difference between chemical and physical changes.

(Emperor-A) Here are some evidence they are-

A colour change

A gas given off

A temperature change

there are 7 ways to spot if a chemical reactions is occurring:

1. A Temperature change

2. A color change.

3. A precipitate is formed (an insoluble substance)

4. A gas is given off.

5. Light may be given off

6. Odor may be given off

7. Sound may be given off

Basically if there are any permanent changes to the object, such as burning, it can be considered a chemical reaction.

Also when there is bubbling or fizzing.

• A new substance may be created
• A change or peak in energy occurs.
• change in appearance of substance(s)
• Temperature change
• Precipitate
• Color change

You can tell when a chemical reaction occurs when there are changes in properties, a color change, and when the changes in properties precipitate.

The color change, Fomation of a precipitate, Formation of gas, and Temperature change

Evolution of a gas

heat/ energy

precipitate forms

color change

evolution of light

You could know by the color change, temperature change, a new substance may be created, etc..

First it changes into a complete different substance

Second it changes energy

Third it may change color

Fourth a solid may appear when two solutions are mixed together

Fifth is a gas might be produced from solids or liquids.

the smell and size.

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The following observations can help you to determine whether a chemical reaction has occurred:

- change of odour (smell)

- change of colour

- change in temperature, e.g. the production or loss of heat.

- change of form, e.g. burning paper

- light, heat, or sound is given off.

- formation of gases, often appearing as bubbles.

- formation of a precipitate (insoluble particles that usually sink to the bottom)

- the decomposition of organic matter, e.g. food rotting

- evident apparition of a new substance with a new chemical formula

There are quite a few indicators that a chemical change may have occurred. These include;- Change in color or luster. The release of gas or vapor. (noticeable odor or formation of bubbles) Change in temperature. (either cooling down or heating up) Formation of a precipitate. The release of heat and/or light & sound. A change in volume. The melting point or boiling point changes. A change in electrical conductivity occurs. A change in any distinctive chemical or physical properties occurs. Not all of these changes are necessarily proof of a chemical change, but they are a good indication and a starting point for further investigation. e.g. ruling out physical changes.

Answer 2

Signs of chemical reactions may be: - Gas release - Formation of a precipitate - Change of color - Change of odor - Change of pH - Change of aspect - Change of viscosity - Change of the temperature - Visible formation of new compounds - Change of the state of the matter - A violent reaction with explosion or fire - Bubbling - Emitting a sound - Emitting a light

Answer 3

if there is an energy change. like if there is heat or light given out

Answer 4

Some examples of a chemical reaction is color change, precipitation, gas production, changes in temperature, and changes in properties.

Answer 5

change of color, change in temperature, bubbling/fizzing.

Answer 6

following evidences:

- change in colour

- evolution of gas

- change in the heat content

etc.

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Answer 7

The reaction products and perhaps absorption or release of energy.

Answer 8

A physical change such as a color difference, temperature difference, or a chemical change such as dissolving or precipitation implies that a reaction had taken place.

Answer 9

The colour may change. Precipitates can be seen. Gas bubbles may occur.