The mechanism of thermal decomposition of matter, the endothermic decomposition of substances

It's been a long time since I've had a systematic chemistry system, and the answer may be a little messy, some of which is a personal understanding, and it may not be correct from the perspective of structural chemistry.

There is indeed some difference between the decomposition of solid heating and liquid heating, which is related to the position of the broken bond of the anion and cation in the dry and solution state.

Generally, when the solid is heated, the covalent bond is broken first, and then the ionic bond is broken, and the decomposition is relatively complete.

caco3=cao+co2

o=c-(o)2]2- ca2+

The ionic bond is more stable, the CA-O bond does not fall off, and the covalent bond is relatively weaker.

The C=O double bond is more stable after heating, and one of the covalent (-O)-Ca falls off and binds to Ca2+ to form CaO. The missing electron pair of c forms a double bond with another -O- and eventually exists in the form of O=C=O.

CaCO3 ionizes in solution and is ionized from ionic bonds, and the covalent forms an ionic cluster, which is difficult to decompose or not decompose under normal conditions.

CaCO3 is soluble in water.

Formation of Ca2+ CO32-

These ions are hydrated in water to form stable hydrated ions, which hinder the decomposition.

In fact, it can also be seen that OH- and CO2 can form a fountain phenomenon, which shows that OH- has a strong absorption capacity for CO2.

CO32- is hydrolyzed in water to form HCO3-, OH-

There is also a very small part of hydrolysis to form H2CO3, reaction heating, H2CO3 decomposes H2O CO2, but because Ca(OH)2 is a strong base, completely ionized in water, the number of CO2 decomposition is much smaller than the number of OH-, the probability of collision is large, CO2 and OH- in the solution combine again to form CO32- to form an equilibrium system. Therefore, it is relatively difficult to decompose.

Ammonia bicarbonate undergoes double hydrolysis in an aqueous solution.

h+hco3-=h2co3

nh4+ +oh-=

First of all, HCO3- forms more H2CO3 in water, and is weakly alkalin, relatively speaking, it is not easy to ionize, absorbs more OH- and less OH- in solution, so the collision probability of CO2 and OH- is reduced, and it decomposes after heating.

In general, salts that can be thermally decomposed in solution are usually salts that undergo double hydrolysis.

It can be explained with equilibrium and non-equilibrium reactions.

Sodium bicarbonate solids decompose into sodium carbonate, carbon dioxide and water at about 60 degrees Celsius, but sodium bicarbonate in aqueous solutions is not easy to decompose when heated, for example, ammonium chloride solids and ammonium chloride aqueous solutions are the same."

First of all. Solid reaction: 2NaHCO3 --Na2CO3 + H2O + CO2

It is a unidirectional, non-equilibrium reaction. The reaction can be carried out to the end.

NaHCO3 dissociates in aqueous solution to produce Na+ and amphoteric compounds, which will be present in water.

1) Hydrolytic equilibrium: HCO3- +H2O <-H2CO3 + OH-

2) Ionization equilibrium: HCO3 - where H2CO3 will decompose in case of heat (H2CO3 --CO2 + H2O).However, as H2CO3 decomposes at first, the pH of the solution also increases, and the hydrolytic equilibrium reaction shifts to the left. Thus the generation of H2CO3 was proposed.

The decomposition reaction stops.

NH4CL is similar.

Solid reaction (unidirectional, non-equilibrium reaction) NH4ClS --NH3G + HCl G

Aqueous solution: (3) The initial decomposition of NH4+ to release NH3 leads to a decrease in the pH of the solution, which pretends to be further decomposition of NH4+. Eventually, the decomposition reaction stops.

But for the aqueous solution of ammonium bicarbonate, it can be decomposed into ammonia, water, carbon dioxide when heated".

This is due to the dissolution of NH4HCO3 in aqueous solution to produce equal amounts of HCO3- and NH4+. The hydrolysis reaction of HCO3- releases OH-, while the ionization product of NH4+ escapes to release H+. The pH effects of the two counteract (i.e., the addition of equations (1) and (3) above).

nh4+ +hco3- -h2co3(co2 + h2o) +nh3

The decomposition reaction can be carried out to the end.

1. From the perspective of bond energy, the chemical bonds of CaCO3 and NH4Cl2 are broken after heating to form new substances.

2. The aqueous solution of ammonium bicarbonate can be decomposed into ammonia, water and carbon dioxide when heated because ammonia, water and carbon dioxide will not generate ammonium bicarbonate in water, and the aqueous solution of sodium bicarbonate can be heated, and a small number of sodium bicarbonate can be decomposed into sodium carbonate and carbon dioxide, which reacts quickly into sodium bicarbonate in water, so the aqueous solution of sodium bicarbonate looks non-reactive when heated. Sodium bicarbonate solids decompose at about 60 degrees Celsius because of the lack of water as a solvent.

General substances (such as CaCO3, NH4Cl2) are decomposed by heat Some salts themselves are easy to decompose when heated.

Endothermic can occur.

Decomposition reactions. 1 Insoluble carbonates, eg.

Barium carbonate. Calcium carbonate.

2 Carbonic acid. Acid salts.

For example. Sodium bicarbonate. Calcium bicarbonate.

Ammonium salt. For example.

Ammonium chloride. Ammonium nitrate.

Ammonium bicarbonate. 4. Insoluble alkali.

For example. Iron hydroxide.

Copper hydroxide. 5. Inactive.

Metal oxides.

For example. Silver oxide.

Mercuric oxide. These are common.

Synthetic ammonia. Nitric acid industry.

n2+3h2==2nh3

4nh3+5o2==4no+6h2o

2no+o2==2no2

Sulfuric acid industry. 4fes2+11o2==2fe2o3+8so22so2+o2==2so3

so3+h2o==h2so4

The endothermic ones basically don't take the test.

That is, cao+h2o==ca(oh)2

There is less heat after the reaction than before the reaction.

It has nothing to do with temperature.

Junior Chemistry - Endothermic and Exothermic phenomena during dissolution.

Endothermic decomposition reaction can occur.

1. Insoluble carbonates, such as barium carbonate, calcium carbonate.

2. Carbonated acid salts, such as sodium bicarbonate and calcium bicarbonate.

3. Ammonium salts, such as ammonium chloride, ammonium nitrate, ammonium bicarbonate, 4, insoluble bases, such as iron hydroxide, copper hydroxide.

5. Inactive metal oxides, such as silver oxide, mercury oxide.

These are common.

Synthetic ammonia nitric acid industry.

n2+3h2==2nh3

4nh3+5o2==4no+6h2o

2no+o2==2no2

Sulfuric acid industry. 4fes2+11o2==2fe2o3+8so22so2+o2==2so3

so3+h2o==h2so4

The endothermic ones basically don't take the test.

That is, cao+h2o==ca(oh)2

The heat after the reaction is less than before the reaction and is independent of temperature.

Redox reactions are all yes, such as the thermal decomposition of potassium permanganate.

Basically, as long as the temperature is high enough, the matter will decompose ......

Thermodynamics is the macroscopic theory of thermal motion. Through the observation, experiment and analysis of thermal phenomena, the basic laws of thermal phenomena are summarized. These experimental laws are the culmination of countless experiences and are applicable to all macroscopic systems.

The conclusions of thermodynamics, like the laws on which they are based, are universal and reliable. However, thermodynamics also has definite limitations, mainly in that it cannot reveal the basic laws of thermodynamics and the microscopic nature of its conclusions, and cannot explain the fluctuation phenomenon.

Dynamics is a sub-discipline of theoretical mechanics that studies the relationship between the forces acting on an object and its motion.

For the study of materials, thermodynamics provides a possible result, that is, it must conform to thermodynamics in order for the material to exist, and this result is a necessary condition; Kinetics, on the other hand, provides a process of how the material is grown, a possibility of actual growth. For example, the study of the growth of semiconductor nanodots needs to be in line with thermodynamic conditions and the specific growth process of semiconductor nanodots needs to be studied with kinetics.

When the temperature is higher than normal temperature, or the decomposition reaction that can only occur when the temperature is heated up, it is called thermal decomposition, and it should be noted that thermal decomposition and pyrolysis are not the same phenomenon.

For example, calcium carbonate decomposes into calcium oxide and carbon dioxide when heated:

caco3 = cao + co2 ↑

On the other hand, some compounds are simply broken down into their constituent elements. Water, when heated to more than 2000 , decomposes into its constituent parts - hydrogen and oxygen

2 h2o = 2 h2 + o2 ↑

Decomposition can be done with the help of a catalyst. For example, hydrogen peroxide decomposes more rapidly, using manganese dioxide:

2 h2o2(aq) =2 h2o(l) +o2(g)↑<

Thermal decomposition is one of the smelting methods of metals. Metal oxides, iodides, carbonyl compounds, etc. are heated to decompose to produce pure metals.