Check the chemical reaction, how to judge that the chemical reaction can be carried out

Hehe, you're really funny, now there are more than 30 million compounds, and 1 million are synthesized every year, where do you say to get you a table?

The largest database where reactions can be found is the Bellstein and Gemmerline database. However, there are only two million commonly used compounds.

Judgment of the spontaneity of a chemical reaction.

1. Spontaneous process: under certain conditions, it can be carried out automatically without external force.

2. Enthalpy judgment: a spontaneous process, the system tends to transform from a state of high energy to a state of low energy. to chemistry.

In terms of reactions, exothermic reactions tend to be spontaneous. However, endothermic reactions are also spontaneous, and there are also non-spontaneous febrile reactions.

3. Entropy change judgment: In a system isolated from the outside world, the spontaneous process will lead to an increase in the entropy of the system.

4. The method of judging the change of free energy g g h t s

g 0, the reaction proceeds spontaneously in the forward direction. g 0, the reaction is in equilibrium. g 0, the reaction proceeds spontaneously in reverse.

A reaction in which the entropy of exothermic increases is certainly a spontaneous reaction.

h＜0，△s＞0，△g＜0

A reaction that entropies decrease endothermically, is certainly a non-spontaneous reaction.

h＞0，△s＜0，△g＞0

An exothermic reaction with reduced entropy, lowering the temperature, favors the spontaneous progress of the reaction. h 0, s 0, g 0 to ensure g, t to be lowered.

A process of increasing entropy by endothermy, raising the temperature, favors the spontaneous occurrence of the reaction. h 0, s 0, to ensure g 0, t should be raised high enough.

2010 National Unified Examination for Enrollment in Colleges and Universities.

Consider thermodynamics first. In the absence of other work, g can be used as a criterion. The electrolysis of water mentioned by the subject belongs to the introduction of other work - electric work.

Many of the promising reactions are actually g>0 reactions, but how can this be achieved? God said, Let there be light. For example, photolysis of water is one of the current research hotspots, and the light energy is clean, and it is obtained from the sun, which is a root benefit ......Far from it.

The introduction of light energy is also the introduction of other works. In addition, g reflects the degree of progression of the reaction, the larger the positive value of g, the smaller the degree of reaction, generally g>40kj mol can be regarded as no reaction. The second thing to consider is kinetics.

In fact, there are many reaction thermodynamic criteria that will find that the reaction should be very thorough, but it is difficult to occur under ordinary circumstances (such as room temperature and pressure without other initiation conditions). For example, hydrogen and oxygen mixing generally require conditions such as "ignition" (triggering a free radical reaction) to violently produce water. This is because the reaction is not a one-step process, and there are many steps in between.

For example, the initial step requires a high amount of energy to activate, which creates kinetic resistance, that is, in the case of hydrogen and oxygen mixing, the system is thermodynamically unstable (thermodynamically it produces water), but it is monetically stable (it is difficult to react with the mixture). Figuratively, it can be illustrated by the mode of climbing the mountain. Again, in the case of hydrogen and oxygen mixing, this system initially stays on a small hill and eventually produces water that can be seen as falling into the Mariana Trench, so it should be advantageous to roll all the way downhill overall.

However, due to the shelving at room temperature, this reaction needs to pass through the height of Mount Everest, so it is difficult to occur without other conditions such as ignition. In short, whether a chemical reaction can proceed requires both thermodynamic and kinetic criteria.

2010 National Unified Examination for Enrollment in Colleges and Universities.

The products produced by sodium in small amounts and excess oxygen are different;

A small amount of sulfur dioxide reacts with lime water to form calcium sulfite, and calcium bisulfite is formed when sulfur dioxide is excessive;

When the reaction between C and O2 is sufficient and inadequate, the product is different;

A small amount of carbon dioxide reacts with caustic soda to form carbonate, and sodium bicarbonate is formed when carbon dioxide is excessive;

The products produced by the reaction of iron and concentrated nitric acid and dilute nitric acid are different, and the excess and small amounts of iron are also different products;

The product of iron oxidation by chlorine gas must be ferric chloride;

Sulfur can only oxidize cu to +1 valence

Answer: Solution: Sodium is used to form sodium oxide in a small amount of oxygen and sodium peroxide in excess oxygen, and the products are different, so it is correct;

A small amount of sulfur dioxide reacts with lime water to form calcium sulfite, and when sulfur dioxide is excessive, calcium bisulfite is generated, and the products are different, so it is correct;

When C reacts with O2 sufficiently, carbon dioxide is generated, and carbon monoxide is generated when it is insufficient, and the products are different, so it is correct;

A small amount of carbon dioxide reacts with caustic soda to form carbonate, and sodium bicarbonate is generated when carbon dioxide is excessive, and the products are different, so it is correct;

Iron and concentrated nitric acid react to form nitrogen dioxide, and dilute nitric acid reaction to produce nitric oxide, the product is different, when the iron is small, it is ferric nitrate that is generated, and when it is excessive, it is ferrous nitrate, the product is different, so it is correct;

The product of iron oxidation by chlorine must be ferric chloride, so it is wrong;

The reaction of copper and sulfur can only produce cuprous sulfide, so it is false

2010 National Unified Examination for Enrollment in Colleges and Universities.

Ask a question [meditate].

How long will it take for the teacher?

Answer 1: The reaction between elemental matter and dilute nitric acid generally produces nitric oxide gas. When oxygen is introduced into the gas, nitrogen dioxide is produced, which is a reddish-brown gas and can therefore be identified.

2. Generally, sodium chloride will cause chloride ions to lose electrons to produce chlorine gas, which is yellow-green at room temperature and pressure, which is easier to identify.

Question: How do you judge the product of some of the other reactions?

Generally, chloride ions lose electrons.

Asking questions is the universal solution.

If you are in the third year of junior high school, there are two categories involved.

One is the reaction between metals and acids and salts, depending on the order of activity of the metal, if it is before hydrogen, it can react, if it is after hydrogen, it can not react, the reaction between metal and salt, to see whether the metal is in front of or behind the metal in the salt, if it is in front, it can not be replaced, that is, it cannot react, and vice versa.

In the second category, the reaction between acids and alkalis is mostly a metathesis reaction, and to be able to react, either water is generated, or there is gas, or there is precipitation. Otherwise, it cannot be reacted.

If it's high school, it's more complicated.

Whether the molecule has changed, that is, whether the chemical formula has changed.

Chemical reaction: The molecules of a substance change, but the atoms do not change. That is, new substances are produced. Definition: In a chemical reaction, the process by which molecules break down into atoms, and the atoms rearrange and combine to form new substances, is called a chemical reaction.

Substance: It is the process by which old chemical bonds are broken and new chemical bonds are formed.

Oxidation reaction: The reaction in which a substance loses electrons when it undergoes a chemical reaction is an oxidation reaction. (The function of obtaining electrons is called reduction).

Complex reaction: also known as complex reaction. In the reactant system, when multiple chemical reactions are carried out at the same time, it is called a composite reaction or a complex reaction (however, the latter name is easily confused with the definition of complex reaction in physical chemistry).

And any of these chemical reactions must be able to exist independently, and the components involved in the reaction must also be able to exist independently.

Chemical reactions. Abbreviation: A + B = C: Two or more elements or compounds to form a complex product. (i.e., a reaction in which two or more substances produce a new substance.) ）

Decomposition reactions. Abbreviation: A = B + C: The compound is broken down into constituent elements or small molecules. (i.e., the reverse reaction of the chemical reaction.) It refers to the reaction in which a compound is broken down into two or more simpler elements or compounds under specific conditions. ）

Metathesis reaction (double substitution reaction).

Ab cd = ad cb: In an aqueous solution (also known as ionized), two compounds exchange elements or ions to form different compounds. (i.e., a reaction in which two compounds exchange components with each other to produce two other compounds.) )

If sodium bicarbonate is said to have a hydrogen product, baCO3

When NaHCO3 is small: NaHCO3+BA(OH)2=BAC3+NaOH+H2O

When NaHCO3 is in excess: 2NaHCO3 + BA(OH)2=BAC3 + Na2CO3 + 2H2O

A chemical change is defined when one molecule comes into contact with another molecule to synthesize a macromolecule; or the molecule is broken apart to form two or more small molecules; Or the reorganization of atoms within a molecule.

The formation of a new substance is a chemical reaction.

Ma Wangye, who disagreed, laughed.