Chemistry displacement, metathesis .

1.Because the valency of an element in a single substance is 0, in a compound, the valency of an element is not 0. In the displacement reaction, the reactants become compounds, and one element in the compound becomes elemental. So there must be a change in valency.

2.Among the four types of reactions, as long as there is a elemental element participating or generated, there must be a valency change, or is it because the valency of the element in the element is 0, and in the compound, the valency of the element is not 0. However, there is no change in the valency of the elements that are decomposed (decomposition reaction) of carbonic acid and generated (chemical reaction).

The metathesis reaction takes place by exchanging components with constant valency. If there is a valency change, it certainly does not meet the definition of a metathesis reaction.

3.More than 5% of these substances is because the solute is not the original K2Ona2o .SO3, etc., but their hydration products KOH, NaOH, H2SO4, etc., are definitely larger than the original 5 grams.

4.The clear solution is relatively "pure", and the turbidity liquid is also mixed with insoluble substances, which requires further treatment.

If you want examples, I'll tell you a few.

1.There are elemental substances and compounds involved in CO combustion. There are elemental substances and compounds that generate the decomposition of mercury oxide.

2.There is not necessarily a change in the valency of the elements in the decomposition reaction and the chemical reaction.

Decomposition of calcium carbonate.

I'll tell you next time I don't have time.

To use an analogy:

BaCl2 + H2SO4 = BaSO4 + 2HCl (This is a typical metathesis reaction, that is, the reaction of salt and acid, the valency of the elements in the compound before and after the reaction does not change, so you pay attention to whether there is a precipitate in the product when writing, water or gas is OK.) ）

Note: Seven common ions in junior high school chemistry that undergo metathesis reactions, H ions + OH ions, = H2O

H ion + CO3 root ion = H2O + CO2

NH4 ion + OH ion = H2O + NH3 mg ion + OH ion = MG (OH).

Ca ion + CO3 root ion = CaCO3

AG ion + CL ion = AGCL

BA ion + SO4 root ion = BASO4

Such as: FeCl3

React with NaOH, Fe is +3 valence, Cl is -1 valence, Na is +1 valence, OH root -1 valence, according to the positive and negative elements in the compound.

The principle that valency algebra is each zero, so.

Builds. The chemical formula is.

Fe(OH)3 and NaCl

Chemical equation.

ca(oh)2+h2so4=caso4+2h2o

It should be as long as the metathesis reaction conditions are met.

Junior high metathesis reactions are divided into four categories.

1. Acids and alkalis.

2. Acids and salts.

3. Alkali and salt.

4. Salt and salt.

Category III and Category IV.

Remember "left dissolves and right sinks".

That is, the reactant must be a soluble product and there must be a precipitate.

These are just regular things.

It is also necessary to apply the law of conservation of mass in the chemical formula, and to remember the solubility of salts (there is an appendix at the end of the chemistry book), and the metathesis reactants neutralized by acids and bases are not necessarily solutions.

The second type: if the reaction is combined, it can form a precipitate or reflect (for example, the reaction of barium nitrate and dilute sulfuric acid can form a barium sulfate precipitate and nitric acid).

PS: It is also important to note the nature of metathesis.

That is, the reactant is a solution.

The product must produce gases (carbon dioxide), water and precipitation.

The reaction in which two compounds exchange components with each other to form two other compounds is called metathesis.

It can be abbreviated as ab cd = ad cb

The essence of the metathesis reaction is that the ions in the solution combine into substances that are difficult to ionize (such as water), insoluble substances or volatile gases, so that the metathesis reaction tends to be completed. (It can be abbreviated as: alkali salt salt salt salt is dissolved in brine, and precipitated gas is generated in water.) )

In order to correctly write the chemical equation of the metathesis reaction, it is necessary to memorize the solubility tables of common acids, bases, and salts, and use the solubility of substances correctly.

(4) Metathesis reaction.

31. Marble and dilute hydrochloric acid (laboratory CO2): CaCO3+2HCl=CaCl2+H2O+CO2

32. Sodium hydroxide and copper sulfate: 2NaOH + CuSO4 = Cu (OH) 2 + Na2SO4

33. Sodium carbonate and hydrochloric acid (fire extinguisher principle): Na2CO3 + 2HCl = 2NaCl + H2O + CO2

34. Potassium carbonate (plant ash) and hydrochloric acid: K2CO3 + 2HCl = 2KCl + H2O + CO2

35. Hydrochloric acid and sodium hydroxide (neutralization reaction): HCl+NaOH=NaCl+H2O

36. Sulfuric acid and sodium hydroxide solution: H2SO4 + 2NaOH = Na2SO4 + 2H2O

37. Sulfuric acid and barium chloride solution: H2SO4 + BACl2 = BASO4 + 2HCl

38. Hydrochloric acid and silver nitrate solution: HCl+AGnO3=AGCL (white)+HNO3

39. Sodium hydroxide and ferric chloride solution: 3NaOH + FeCl3 = Fe (OH) 3 (reddish brown) + 3NaCl

40. Barium carbonate and dilute nitric acid: BaCO3 + 2Hno3 = Ba(NO3)2 + CO2 + H2O

41. Sodium sulfate and barium chloride: Na2SO4 + BACl2 = BaSO4 + 2NaCl

42. Sodium chloride and silver nitrate: NaCl + Agno3 = AgCl + Nano3

43. Sodium carbonate and lime water: Na2CO3 + Ca(OH)2=CaCO3 +2NaOH

44. Aluminum hydroxide and hydrochloric acid: Al(OH)3+3HCl=ALCL3+3H2O

45. Ammonium nitrate and sodium hydroxide: NH4NO3 + NaOH = = nano3 + H2O + NH3

46. Iron hydroxide and sulfuric acid: 2Fe(OH)3+3H2SO4=Fe2(SO4)3

47. Hydrochloric acid rust removal: Fe2O3 + 6HCl = 2FeCl3 + 3H2O

48. Copper oxide and sulfuric acid: CuO+H2SO4=CuSO4+H2O

1) Elemental metal + acid - salt + hydrogen (replacement reaction) pre-hydrogen metal, acid is hydrochloric acid or dilute sulfuric acid.

2) Elemental metal + salt (solution) - another metal + another salt.

Elemental metals are pre-metal in salts (except potassium, calcium and sodium), and salts must be soluble in water.

3) Basic oxide + acid --salt + water.

The acid is soluble in water. 4) Acidic oxide + alkali - salt + water.

The alkali is soluble in water (not a metathesis reaction).

5) Acid + Base --Salt + Water.

At least one of acids and bases is soluble in water.

6) Acid + Salt – Another acid + another salt.

The insoluble salt of the junior high school is carbonate, and the acid is soluble and produces gas.

The reactants are soluble in water and form salts as precipitates.

7) Alkali + Salt – Another alkali + another salt.

The reactants must be soluble, and the ammonium salt is gaseous, and the non-ammonium salt must be precipitated.

8) Salt + Salt – Two new salts.

The reactants should be soluble, and the products should be precipitated.

No, the product is required to have precipitation or gas formation, independent of the reactants.

CaCO3 cannot react with Cuci2 as the product has neither gas nor precipitation.

Gas, precipitate or water can be formed in order for the reaction to occur.

There is gas, precipitation or water generation.

Your statement is not entirely correct.

When an equal mass of hydrogen is generated, the number of electrons transferred in the displacement reaction is constant. If the two metal atoms lose the same number of electrons in the reaction (i.e., the same valency), then the same number of metal atoms required to transfer the same number of electrons to hydrogen is also the same.

The relative atomic mass of a metal is directly proportional to the mass of each metal, so the greater the relative atomic mass of a metal with the same number of metal atoms, the greater its mass.

In summary, if the metal atoms lose the same number of electrons in the reaction (i.e., the valency is the same), then the same mass of hydrogen is generated, and the greater the relative atomic mass of the metal, the greater the mass consumed by the reaction.

If the valencies of the metals are different, then each metal atom loses a different number of electrons and cannot be specifically compared.

First of all, all displacement reactions must not be metathesis reactions, but redox reactions, which is a fundamental problem and cannot be wrong. ‘

Secondly, the displacement reaction is characterized by the replacement of an active element with another inactive element, so both reactants and products should contain elementals, such as iron and copper sulfate, sodium and water, and even the reaction of iron and dilute sulfuric acid are all displacement reactions.

Elemental + Compound Another elemental + another compound.

The displacement reaction is a chemical reaction in which an element reacts with a compound to form another element and compound, and any displacement reaction is a metathesis reaction, which can be expressed as: A+BC B+AC The displacement relationship refers to the substitution of an element that makes up a compound by an element that makes up the element.

Elemental and compound reactions to generate elemental and compound reactions! For example, Zn+H2SO4=ZnSO4+H2.

As long as it causes a decrease in the concentration of ions in the solution, a metathesis reaction may occur.

Regarding the conditions of metathesis reaction: there is precipitation, gas, and water formation, and in high school, it will expand to the formation of substances that are difficult to dissolve, difficult to ionize, and volatile.

Hydrochloric acid is a strong acid that is completely ionized in water, which means that Cl- is difficult to bind to H+ in a dilute solution; Carbonic acid, on the other hand, is a weak acid, that is, a substance that is difficult to ionize, and is not easily ionized in water, which means that CO32- is easily combined with H+.

When CO32- meets H+ in water, it binds to HDO3- or H2CO3, which is difficult to ionize, depending on the ratio of HCl to CO32- added.

In fact, this is not the case.

It's a step-by-step response.

Step 1: Na2CO3+HCl=NaHCO3+NaCl Hydrochloric acid is a small amount at this time.

Step 2: NaHCO3+HCl=NaCl+H2O+CO2 This reaction will occur when sufficient hydrochloric acid is sufficient.

So, the two merged.

The chemical equation: Na2CO3+2HCl=2NaCl+H2O+CO2 is the standard metathesis reaction.

The phenomenon seen in this process is that there is no obvious phenomenon at first, and then bubbles are produced.

Huaxuehelaoshi's answer is correct, but not all metathesis reactions move in the direction of decreasing ion concentrations, such as the reaction of ammonia with acetic acid.

It's very simple and general: Na2CO3 + 2HCl == 2NaCl + H2O + CO2

When there is an excess of Na2CO3, the produced H2O and CO2 and Na2CO3 produce sodium bicarbonate.