Physical change, chemical change, physical phenomenon, how to distinguish chemical phenomenon!

A physical change is a change in which no new matter is generated. For example, solid ice is heated and melted into water, and liquid water evaporates into water vapor; Water vapor condenses into water, and water solidifies into ice. In the three states of water, only the shape and state of the water have changed.

No new matter is produced, so it is a physical change. Another example is diffusion, aggregation, expansion, compression, volatilization, sublimation, frictional heat generation, iron to magnet, energized heating and luminescence, activated carbon adsorption chlorine (8 kinds?) And so on are physical changes.

The transformation of graphite into diamond under certain conditions is not a physical change, but a chemical change, because it becomes another element. Before and after the physical change, the type, composition, and chemical properties of the substance remain the same. The essence of this type of change is a change in the state of aggregation of molecules (separation distance, rate of motion, etc.), resulting in a change in the shape or state of the substance.

Physical changes express the physical properties of the substance. Physical change is fundamentally different from chemical change.

A chemical change is a change that is produced by a new substance, which is called a chemical change, also known as a chemical reaction. Chemical changes are prevalent in production and life. Such as the rust of iron, the fireworks of festivals, the neutralization of acid and alkali, and so on.

On a macroscopic scale, it can be seen that various chemical changes produce new substances, which is characteristic of chemical changes. The essence of chemical change can be understood from a microscopic perspective: the type and number of atoms before and after the chemical reaction do not change, but only the way the atoms bond with each other changes.

For example, in the case of a substance made up of molecules, it is a molecule in which atoms are recombined into a new substance. The chemical properties of a substance can only be expressed through chemical changes in the substance, so the chemical properties of the substance can be studied by the method of making the substance react chemically and a new substance can be prepared.

Physical Change: (No new matter generated).

Three-state changes of gas-solid-liquid of the same substance (melting of iron into molten iron; Water vaporization into water vapor; Oxygen liquefaction to liquid oxygen, etc.); cutting glass, steel; Fractionation of petroleum.

Chemical Change: (New substance is generated).

The rice is cooked; cracking the oil; lit matches, pieces of paper; Put zinc granules into dilute sulfuric acid; Heat the copper block in the air....

Look at whether the chemical formula of the molecules that make up the substance has changed.

The difference between a physical change and a chemical change is whether or not a new substance is formed.

Connection: There must be physical changes in the process of chemical change, and the process of physical change may be accompanied by chemical change.

Physical Changes: No changes in the formation of other substances. For example: a light bulb glows, ice melts into water; Water evaporates into water vapor; Iodine, sublimation of dry ice, volatilization of gasoline, melting of candles, etc., are all physical changes.

Chemical change: A change in the formation of other substances when a substance changes. For example: wood burns, iron rusts, food rots.

Chemical changes are often accompanied by some reaction phenomena while generating new substances, such as color changes, gas release, precipitation, etc., chemical changes not only generate other substances, but also accompanied by energy changes, which are often manifested as endothermy, exothermic, luminescence, etc.

1. Physical properties.

Physical properties refer to properties that can be exhibited without chemical changes, such as color, state, odor, melting point, boiling point, hardness, density, etc. For example, nitrogen is a colorless, odorless gas with low melting and boiling points.

2. Chemical properties.

The properties of substances exhibited in the changes of chemical wheel source are called chemical properties, such as flammability, stability, reduction, oxidation, etc.

Chemical properties need to undergo chemical changes to manifest, such as hydrogen is flammable, this property can only be manifested in the chemical reaction of hydrogen combustion, so it is a chemical property; Physical properties, on the other hand, are physical quantities that can be perceived and measured.

3. Chemical changes.

When the change produces other substances, it is called a chemical change, also called a chemical reaction. For example, the burning of firewood and the rusting of steel all form new substances, both of which are chemical changes.

In the process of chemical change, in addition to the formation of other substances, there are also some phenomena such as heat release, luminescence, discoloration, gas release, precipitation, etc., which can often help us judge whether chemical changes have occurred, but they are not the essence of change.

4. Physical changes.

The absence of other substances is called a physical change. For example, the vaporization of liquid water into water vapor by heat is a physical change.

The essential difference between physical change and chemical change is whether or not other substances are formed. For example, the chemical change of sulfur dioxide produced by sulfur combustion is a chemical change in the wax state, and the absence of other substances when the lamp is energized and emitted is a physical change.

Physical change is related to chemical change, and physical change occurs at the same time as chemical change occurs, but chemical change does not necessarily occur in the process of physical change.

1) Do not use the phenomenon of chemical change as the basis for judging physical and chemical changes.

2) The difference between the change of matter and the properties of matter.

A change in matter, whether physical or chemical, refers to a dynamic process, while the properties of matter, whether physical or chemical, refer to properties specific to matter.

Differences: 1. Chemical change: chemical change refers to the conversion or transfer of atoms or electrons between molecules in contact with each other, and the process of generating new molecules accompanied by energy changes, the essence of which is the breaking of old bonds and the formation of new bonds.

The process of chemical change is always accompanied by physical change. In the process of chemical change, there are usually luminescence, exothermia, and endothermy. According to the atomic collision theory, the chemical change between molecules is accomplished through collision, and two conditions are required to complete the collision reaction molecule: (1) sufficient energy and (2) correct orientation.

Because the reaction needs to overcome a certain molecular energy barrier, it must have a higher energy to overcome the molecular energy barrier. Two colliding molecules must have the correct orientation for the old bond to break. 2. Physical changes:

Physical change refers to the process of change in which no new matter is formed. A mixture of pure substances into a mixture is a physical change; The separation of a pure substance from the mixture is also a physical change. Judgment:

1. Whether there is a new substance generated, if a new substance is generated, a chemical change has occurred. 2. Physical changes are generally deformation, like liquefaction and solidification. Examples:

1. Water evaporation - liquid water becomes gaseous water, and there is no new substance generated, which is a physical change. 2. Iron rusts - Iron becomes rust, and rust is a new substance. The change is a chemical change 3, the candle burns - the paraffin wax becomes carbon dioxide and water, and carbon dioxide and water are new substances.

The change is a chemical change.

Difference Between Chemical Change and Physical Change.

The biggest difference between physical change and chemical change is that physical change does not produce new substances, while chemical changes produce new substances.

Chemical changes must contain physical changes, and there must be no chemical changes in physical changes.

Judgment method: According to the essential characteristic of "whether other substances are generated" in the change, it is possible to distinguish between physical change and chemical change. "Formation of other substances" is the only basis for judging chemical changes.

The phenomena accompanying the change process, such as luminescence, heat release, color change, gas release, precipitation generation, etc., only play a certain auxiliary role and cannot be used as the basis for judging chemical changes.

For example, if you pour a spoonful of baking soda into a cup and then add an appropriate amount of white vinegar, we can see a noticeable change in the cup, like a carbonated drink after shaking.

This step is a chemical change, because the white vinegar and baking soda are mixed to produce a large number of bubbles, which are the new substance "carbon dioxide" that is generated.

1. Differences. 1. Essential differences: no new matter is generated during physical changes; Chemical changes lead to the formation of new substances.

2. Accompanying phenomena: physical changes, changes in the form of substances, generally no obvious light and heat phenomena, and the color and state of substances may change; Chemical changes generally have obvious light and heat phenomena.

3. The relationship between the two: there must be no chemical change in the physical change; Chemical changes are often accompanied by physical changes.

2. Judgment. To judge whether a chemical change has occurred, it is only necessary to judge whether a new substance is produced, and the change produced by a new substance is a chemical change.

3. Examples. Examples of chemical changes: sodium hydroxide.

Metamorphism, plant photosynthesis, hydrochloric acid rust removal, basic copper carbonate.

Decomposes by heat, iron rusts in moist air, and copper oxide is reduced with hydrogen.

Examples of physical changes: water evaporation and solidification, sugar lump melting, carbon dioxide.

Condensed into dry ice.

Iodine is sublimated into purple vapor, long-term flour lumps, NaOH and other inorganic salts when heated.

Deliquescence of alkalis. <>

The main difference between physical change and chemical change is the formation of new substance. Whether a chemical change occurs depends on whether a new substance is eventually formed.

1. Overview of physical and chemical changes:

1. Physical change: There is no change in the formation of new matter (physical change is only a change in the shape and state of matter). Substance: The smallest particle that maintains the chemical properties of the substance itself remains the same, except that the spaced motion between the particles changes, and no new matter is generated.

2. Chemical change: the process of conversion or transfer of atoms or electrons between molecules in contact with each other to generate new molecules accompanied by energy changes; The chemical change is essentially the breaking of the old bond and the formation of a new bond.

2. Examples of physical changes:

1. Water evaporation. Liquid water becomes gaseous water, and there is no new substance formed, which is a physical change.

2. Solid dry ice is used to create stage effects, solid dry ice is solid carbon dioxide, which is placed on the stage and instantly sublimated into gaseous carbon dioxide, forming a fairyland, not forming a new substance, which is a physical change.

3. The volatilization of gasoline only undergoes deformation, and the substance itself does not change.

4. Wood is made into tables and chairs, and no new substances are generated in the process.

3. Examples of chemical changes:

1. Iron rust. Iron turned into rust, and rust is a new substance. The change is a chemical change.

2. Candle burning. Paraffin wax becomes carbon dioxide and water, and carbon dioxide and water are new substances. The change is a chemical change.

3. H2 and O2 mixed ignition**, etc. Because the molecules before and after the reaction are different.

Note: Nuclear changes (nuclear fusion, nuclear fission) are not chemical changes but physical changes.

Look at whether the substance itself changes, that is, whether there is a new substance generated, the change generated by a new substance is a chemical change, and the change without the formation of a new substance is a physical change. If water freezes, although the state has changed, it is still water, but it is only solid water, which is a physical change. Another example is iron rusting, after rusting, it is no longer a substance like iron, so it is a chemical change.

Yes, this question is very confusing at first, because there are phenomena, and how to see the essence through the phenomena will know whether it is a chemical change or a physical change.

For example, CO2 turns red when it is introduced into a purple litmus solution. From purple to red, this is a phenomenon, behind the phenomenon is the essence, what is the essence, that is, because CO2 and H2O can react, the production of H2CO3 H2CO3 can be acidic to make the purple litmus solution red, and CO2 itself cannot, so a chemical reaction occurs.

The dissolution of white sugar, the white sugar is put into water, and the solid will dissolve after a while, which is also a phenomenon, the solid white sugar and the dissolved white sugar are still the same substance, so it is a physical change.

In the beginning, many phenomena like this need to be memorized and accumulated, and it is not possible to understand them all at once.

The molecular composition of the chemically changed substance will change, simply put, it will produce a new substance, and the physical change is only a change in shape or solid-liquid gas, and will not produce a new substance.

A chemical change is to produce a chemical reaction, and a physical change is to produce a physical reaction, which is very simple.

Chemical reactions to see if new substances are formed. Except for nuclear reactions.

What is the difference and connection between physical change and chemical change.

Difference Between Chemical Change and Physical Change.

Difference Between Physical Change and Chemical Change.

When there is a change, there is no change in other substances, which is called physical change. For example, water turning into water vapor, crushing stones, iron making nails, and so on are all physical changes.

When it changes, it produces changes in other substances, which is called chemical change. For example, alcohol burning, wood burning, food deterioration, respiration, etc., all produce changes in other substances when they change, so they are all chemical changes.

The essential difference between physical change and chemical change is that it looks at whether other substances are formed during the change, which is also the basis for judging physical change and chemical change.

The main difference is whether or not new substances are generated; The formation of a new substance is a chemical change, otherwise it is a physical change.

The main thing is to see if there is a new substance formed during the change.

The main difference between a physical change and a chemical change is whether or not a new substance is formed.

The main characteristic of chemical change is that it usually emits light during chemical reactions. Exothermic. Produces color variations.

generation of precipitation, etc. The most important thing to judge whether a substance has undergone chemical change is to see whether a new substance has been formed. Such as magnesium burns in the air, glowing.

Exothermic, magnesium oxide is formed.