Important reaction phenomena in junior high school chemistry. Principles of various chemical reactio

There are many precipitates in the chemical reactions learned in junior high school, especially the part of acid and alkali salts, which can produce magnesium hydroxide, barium sulfate, silver chloride, barium carbonate, calcium carbonate, copper hydroxide, iron hydroxide, etc., which are precipitated, of which the first five are white, copper hydroxide is blue, iron hydroxide is reddish-brown, and the most important reaction of heating is calcium oxide and water reaction, in addition, concentrated sulfuric acid dilution and sodium hydroxide deliquescent are also exothermic.

The more important ones left are 1The reaction between iron and copper sulfate is as follows: there is a red substance on the surface of silvery-white iron, and the solution changes from blue to light green;

2.Reaction between aluminum and copper sulfate: a red substance is formed on the surface of silvery-white aluminum, and the solution changes from blue to colorless (or the color of the solution becomes lighter).

3.All reactions in which gas is formed are bubbles;

4.Iron burns violently in pure oxygen to produce black matter.

Be careful not to include the name of the product when describing the phenomenon.

The neutralization reaction will heat up, and calcium oxide dissolved in water to form calcium hydroxide is also a warming reaction, and both metal and acid reactions are. It is enough to memorize these in junior high school chemistry. Precipitation!

Carbonate precipitates with magnesium, barium, calcium, manganese, zinc, silver, and ferrous ions. Calcium sulfate, silver sulfate is slightly soluble, barely precipitated, and barium sulfate is a precipitate. Silver chloride is a precipitated barium sulfate and silver chloride is insoluble in either water or acid, nitrate does not precipitate.

Alkalis are soluble in potassium, sodium, barium, and ammonium. The rest is insoluble. In the order table of metal activity, the pre-hydrogen metal reacts with the acid to produce hydrogen, and the marble limestone reacts with the acid to produce carbon dioxide.

If you don't have much content in junior high school chemistry, I don't mind if you buy a reference book that is synchronized with the textbook, and many of the books summarize it better.

The general reaction is an exothermic reaction, and individual endothermic reactions. Just memorize what you absorb heat. Like precipitation, you can summarize it yourself and ask the teacher, and the teacher has induction.

The principles of various chemical reactions in junior high school are as follows:

1. Heat of reaction and enthalpy change: h=h(product)-h(reactant).

2. The relationship between the heat of reaction and the energy of the matter: the internal energy between different substances is different, and the energy is conserved in the whole reaction process, and the energy difference between the reactant and the product is manifested as endothermic or exothermic in the form of heat.

3. The relationship between the heat of reaction and the bond energy: h = the sum of the bond energy of the reactant - the sum of the bond energy of the product and the sum of the spring energy.

4. Common endothermic and exothermic anti-Sentong should:

Common exothermic reactions: reaction of active metal with water or acid, acid-base neutralization reaction, combustion reaction, chemical reaction of most aging, thermite reaction.

Common endothermic reactions: most of the decomposition reactions are 2NH4Cl(S)+BA(OH)2 8H2O(S)=BACl2+2NH3+10H2O

c(s)+ h2o(g) co+h2 ④co2+ c2co

5. The relationship between reaction conditions and endothermic and exothermic: Whether the reaction is endothermic or exothermic is not necessarily related to the conditions of the reaction, but depends on the relative magnitude of the total energy (or enthalpy) possessed by the reactants and products.

6. Metal corrosion: corrosion caused by electrolytic anode, corrosion caused by galvanic battery anode, chemical corrosion, galvanic battery cathode, electrolytic cathode.

Iron and steel is mainly corroded by oxygen absorption in the air. Negative electrode: 2Fe 2Fe2++4E- Positive electrode: O2+4E-+2H2O 4Oh-

Total reaction: 2Fe + O2 + 2H2O = 2Fe (OH)2.