-
Anonymous users2024-02-071 Exothermic reaction: (+q).
1) All combustion or ** reactions.
2) Acid-base neutralization reaction.
3) Most chemical reactions.
4) The reaction of active metals with water or acids to form H2.
5) Slow oxidation of substances.
6) Spontaneous redox reactions.
2 Endothermic reaction: (-q).
1) Several common reactions, such as: 2NH4Cl(S)+BA(OH)2·8H2O(S)=BACl2+2NH3 +10H2O C+H2O(G)=CO+H2 C(S)+CO2(G)=2CO
Most of the decomposition reactions, such as: CaCO3 = (high temperature) CaO+CO2 CuSO4·5H2O=CuSO4+5H2O
Dissolution of some substances, such as ammonium nitrate dissolution, etc. (It can also be said to be the hydrolysis of salts, which must be an endothermic reaction at this time.) For example, ammonium root hydrolysis is endothermy).
2) Special endothermic reactions, such as: C+CO2=2COi2+H2=2HI (this reaction is reversible, because the generated hydrogen iodide is unstable).
The essence of chemical reaction is: the breaking of old bonds and the formation of new bonds, and the newly formed chemical bonds are generally more stable than the old bonds, covalent electrons transition from high energy levels to low energy levels, releasing energy, and the breaking of old bonds needs to absorb energy, so the final chemical reaction is endothermic or exothermic to see the difference between energy changes before and after the reaction, if the energy is insufficient, it needs to be endothermic from the outside, and vice versa, usually we use enthalpy change (h) to measure the thermal phenomenon before and after the reaction. If there is anything you don't understand, you can continue to ask, and I'll be happy to help you answer.
-
Anonymous users2024-02-06Universities rely on the standard enthalpy of each substance to calculate.
Middle School Exams! Endothermic reactions: most of the decomposition reactions, C, Co, H2 reduction of metal oxides, barium hydroxide with eight crystalline water and ammonium chloride reaction, most of the salt hydrolysis reactions.
Exothermic reactions: most of the chemical reactions, acid-base neutralization reactions, metal-acid reactions, metal-water reactions, combustion reactions.
Actual life test test test measurement!
-
Anonymous users2024-02-051. Judging according to the relative stability of reactants and products: the reaction of forming an unstable substance from a stable substance is an endothermic reaction, and the opposite is a reaction that releases energy.
2. Judging from the reaction conditions, all reactions that can be carried out by continuous heating are generally endothermic reactions, and vice versa, reactions that release energy.
3. According to the relative size of the total energy of the reactant and the product, if the total energy of the reactant is greater than the total energy of the product, the energy will be released during the reaction, otherwise the energy will be absorbed.
C, H2, Co as a reducing agent reaction are endothermic.
Explanation: The two criteria for judging the thermal effect of the reaction are experimental measurements and calculations through thermodynamics, while C, H2, and CO reductions are exothermic reactions in many cases, such as the following examples:
Reaction 1: Cuo(S)+H2(G)=Cu(Cr)+H2O(G).
Reaction 2: Cuo(S) + Co(G) = Cu (Cr) + Co2 (G).
Reaction 3: Cuo(S) + (graphite) = Cu(Cr) + CO2(g).
Calculating the thermal effects of chemical reactions can be used directly using δH, and the effect of temperature on δH is ignored here.
-
Anonymous users2024-02-04Chemically, a chemical reaction that absorbs heat is called an endothermic reaction. The total energy of the reactants in an endothermic reaction is lower than the total energy of the products.
The decomposition reaction is generally an endothermic reaction, such as 2NaHCO3 = (heating) Na2CO3 + H2O + CO2
Several common endothermic reactions such as:
2nh4cl(s)+ba(oh)2·8h2o(s)=bacl2+2nh3↑+10h2o
c+h2o(g)=co+h2
The dissolution of some substances, such as ammonium nitrate dissolution, is also an endothermic reaction.
Note: Reactions that do not need to be heated are endothermic reactions, and most of them are required for combustion"Ignite", all of which are exothermic reactions.
Whether it is exothermic or not mainly depends on whether the total energy of the reactant is greater than the total energy of the product. Most chemical reactions are exothermic. The redox reactions that can be carried out spontaneously are exothermic reactions, and the combustion reactions and neutralization reactions in the common reactions are all exothermic reactions, and the common exothermic reactions:
1.All combustion or ** reactions.
2.Acid-base neutralization reaction.
3.Most chemical reactions.
4.Reaction of active metals with water or acids to form H2.
5.Slow oxidation of substances.
6.Spontaneous redox reactions.
-
Anonymous users2024-02-031. There are several methods for judging exothermic reaction and endothermic reaction:
1) According to the relationship between the total energy of the reactant and the total energy of the product, the total energy of the reactant is higher than the total energy of the product, and the reaction is an exothermic reaction. The total energy of the reactant is lower than the total energy of the product, and the reaction is endothermic.
2) According to the relationship between the sum of bond energies possessed by reactants and the sum of bond energies possessed by the products: δh = total bond energy of reactants - total bond energy of the products, if the total bond energy of the reactants is greater than the total bond energy of the products, then δh 0, the reaction is endothermic reaction. If the total bond energy of the reactant is less than the total bond energy of the product, then δh 0 and the reaction is exothermic.
3) According to the basic type of chemical reaction: the acid-base neutralization reaction is an exothermic reaction; Most displacement reactions are exothermic reactions; The vast majority of chemical reactions are exothermic reactions; Most of the decomposition reactions are endothermic; Salt hydrolysis reaction, ionization is an endothermic reaction.
2. Exothermic reaction.
In a chemical reaction, a reaction in which the total energy of the reactants is greater than the total energy of the products is called an exothermic reaction. These include combustion, neutralization, metal oxidation, thermite reactions, more reactive metal reactions with acids, and reactions from unstable substances to stable substances.
3. Endothermic reaction.
Endothermic reaction refers to a chemical reaction that is chemically characterized by the absorption of heat. The total energy of the reactants in an endothermic reaction is lower than the total energy of the products. The reverse reaction of an endothermic reaction must be an exothermic reaction.
-
Anonymous users2024-02-021 Exothermic reaction: (+q).
1) All combustion or ** reactions.
2) Acid-base neutralization reaction.
3) Most chemical reactions.
4) The reaction of active metals with water or acids to form H2.
5) Slow oxidation of substances.
6) Spontaneous redox reactions.
2 Endothermic reaction: (-q).
1) Several common reactions, such as: 2NH4Cl(S)+BA(OH)2·8H2O(S)=BACl2+2NH3 +10H2O C+H2O(G)=CO+H2 C(S)+CO2(G)=2CO
Most of the decomposition reactions, such as: CaCO3 = (high temperature) CaO+CO2 CuSO4·5H2O=CuSO4+5H2O
Dissolution of some substances, such as ammonium nitrate dissolution, etc. (It can also be said to be the hydrolysis of salts, which must be an endothermic reaction at this time.) For example, ammonium root hydrolysis is endothermy).
2) Special endothermic reactions, such as: C+CO2=2COi2+H2=2HI (this reaction is reversible, because the generated hydrogen iodide is unstable).
The essence of chemical reaction is: the breaking of old bonds and the formation of new bonds, and the newly formed chemical bonds are generally more stable than the old bonds, covalent electrons transition from high energy levels to low energy levels, releasing energy, and the breaking of old bonds needs to absorb energy, so the final chemical reaction is endothermic or exothermic to see the difference between energy changes before and after the reaction, if the energy is insufficient, it needs to be endothermic from the outside, and vice versa, usually we use enthalpy change (h) to measure the thermal phenomenon before and after the reaction. If there is anything you don't understand, you can continue to ask, and I'll be happy to help you answer.
-
Anonymous users2024-02-01Look up the table Every substance has its heat of melting, heat of vaporization, and specific heat capacity.
The amount of heat absorbed by the temperature from absolute zero to its present temperature is the internal energy of the solid.
Starting from absolute zero, the heat absorbed by it to its melting point + the heat of melting + the heat required to rise to the current temperature = the internal energy of the liquid.
Starting from absolute zero, the heat absorbed to its melting point + heat of melting + heat required from melting point to boiling point + heat of vaporization + heat required to rise to the present temperature = internal energy of the gas.
After using the internal energy for a long time, you can know whether it is endothermic or exothermic, 2, how to judge whether the reaction is endothermic or exothermic?
If the total energy possessed by the reactant is greater than the total energy possessed by the product, the reactant releases heat when it is converted into the product, which is an exothermic reaction.
If the total energy of the reactant is less than the total energy of the product, the reflectant needs to absorb heat to convert into the product, which is an endothermic reaction.
But how can you tell if the total energy of the reactant is greater or less than the total energy of the product? Give an example.
-
Anonymous users2024-01-31In general, the following reactions are exothermic reactions:
1.Combustion of combustibles (exothermic, for sure).
2.Acid-base crack shouts and (definitely exothermic).
3.The metal reacts with the acid.
4.The reaction conditions are:"Ignition at the source of ignition"such as the combustion of iron in chlorine gas.
In general, the following reaction is endothermic reaction:
1.The reaction conditions are:"Heating"
2.The reaction conditions are:"High temperatures"
3.Some special reactions, such as the mixed grinding of macroridge ammonium chloride solids with barium hydroxide crystals.
The above generalization is just"General", in which some special reactions will also occur, such as:
Fe + S = Heating = Fes
This reaction is conditioned on:"Heating", but the reaction itself is an exothermic chemical reaction.
1) Yes, as long as it is the substance in the equation.
2) The reaction rate ratio of O2 and SO2 is 11:8, so when the rate of SO2 generation is, the rate of O2 consumption is. >>>More
According to the principle of conservation of mass, the mass of a substance before and after the reaction must be equal, and whether a substance has a chemical reaction cannot be judged according to whether the mass is equal or not. >>>More
Esterification reaction is a class of organic chemical reactions, which is the reaction of alcohol with carboxylic acid or oxygenated inorganic acid to produce ester and water. It is divided into two categories: carboxylic acid reaction with alcohol and inorganic oxygenated acid reaction with alcohol, and inorganic strong acid reaction with alcohol. The esterification reaction of carboxylic acid and alcohol is reversible, and the reaction is generally very slow, so concentrated sulfuric acid is often used as a catalyst. >>>More
After the trim equation, look at the valency change.
Generally speaking, the higher the temperature, the faster the reaction, the lower the temperature, the slower the reaction, which is not only a familiar phenomenon for chemists, but also a common sense of people's life, the room temperature is high in summer, and the food is easy to rot and deteriorate, but the food in the refrigerator can be stored for a longer time. The oxidation reaction rate of steel at room temperature is extremely slow, which is greatly accelerated with the increase of temperature, and a large amount of iron oxide scale has been produced when it is red-hot. The reaction of hydrogen and oxidation to form water can not be detected for several years at room temperature, and if it is heated to 973K, it will be completed instantaneously at the rate of **. >>>More