How to tell which substances react and which don t react in a chemical reaction

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.

To determine which substances react, first of all, you must have a clear understanding of the chemical reactions in the textbook.

How to judge the method:

1. For substances that react with oxygen, they must be flammable, and flammable substances can react with oxygen when ignited.

2 For chemical reactions: as long as it is a reactive metal, it can react with a reactive non-metal (oxygen, chlorine).

3. Decomposition reaction: As long as the material is unstable under certain conditions, it can be decomposed. Such as potassium chlorate, potassium permanganate, hydrogen peroxide, insoluble carbonate, bicarbonate, etc.

4. Displacement reaction: In the solution, the strong reactivity replaces the weak reactive, and the strong replaces the weak.

5. Metathesis reaction: The product must be generated by water, gas, and precipitation before the reaction.

Reactants salts and bases, salts and salt reactants must be soluble in water.

6. Redox reaction: oxidizing substances can react with reducing substances.

Some special reactions can only be memorized.

To put it simply: from the point of view of phenomena, after the reaction, it can be converted into substances in the form of gas, precipitation, weak electrolytes or complexes, and reactions can occur; Essentially, a substance can react if the reaction can cause the old bonds to break and new ones to form.

The change in Gibbs free energy of the reaction can be calculated According to the second law of thermodynamics, no non-volumetric work is done in a constant temperature and constant pressure system, and the direction in which the Gibbs free energy decreases is the direction in which the reaction proceeds. For example, water cannot be decomposed under standard conditions, but it can be decomposed into oxygen and hydrogen under the condition of doing electrical work, that is, electrolysis, but oxygen and hydrogen can react spontaneously to produce water, and the reaction is extremely slow, requiring a catalyst. The energy reaction is a thermodynamic problem, and the speed of the reaction is a kinetic problem.

Measure the mass of each substance before and after the reaction, the unchanged will not react, and the changed will react.

In the case of displacement reactions, it depends on the activity, and in the metathesis reactions, it depends on whether it can generate precipitates or water or gas 、、、

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In a chemical reaction, how to tell if the reaction is prone to occur.

Hello, knowing the free energy function of two reactions, it is also impossible to judge whether it is easy to carry out or not. If we know the standard Moore reaction Gibbs function of two reactions, we can know the degree of reaction when they reach equilibrium; Combined with the Molar reaction Gibbs function of the two reactions, the isothermal equation is used to determine whether the reaction is easy or not. "How to tell if a chemical reaction can occur; First of all, it is necessary to know how many kinds of chemical reactions there are1.

Neutralization reaction, that is, the reaction between acid and base, depends on the reaction conditions, if it is in water, it is insoluble, and it is not reflected2. Metathesis reaction There are 2 salts [or others] in the reaction product that do not allow substances or gases3. Displacement reactions, such as the displacement of metals by reducing gases, the reaction of halogens and halogen compounds.

4.The redox reaction mainly depends on whether the two substances have opposite redox properties. In chemistry at the middle school level, there are some rules to follow in judging whether substances react with each other.

If the force is weak, the strong acid and strong alkali produce a weak acid and weak alkali, so that it can react, and in turn, the weak acid and weak alkali cannot make a strong acid and strong alkali. It can also be judged by the relative redox strength, which is also coercive. However, whether specific substances can react with each other depends on whether there is such a reaction in reality, and these laws cannot be used to fabricate non-existent reactions.

Conceptually, when something new is formed, a chemical reaction takes place. As for whether the half-phase reaction can occur or not, the chemical phenomenon is characterized by the reaction rate, and it is only under non-equilibrium conditions that the chemical reaction process will show a non-zero reaction rate. When it is not in equilibrium, the substance reacts.

In the case of isolated systems, any change in reaction that occurs in them is necessarily spontaneous. The second law of thermodynamics tells us that any change or chemical reaction that occurs in an isolated system always proceeds in the direction of increasing entropy, i.e., in the direction of s isolation》0.

And when equilibrium is reached, sisol=0, at which point the entropy reaches its maximum. If it is not an isolated system, the system and its surroundings can be considered as a new isolated system, and the entropy increase principle is still applicable. From this, it can be concluded that the spontaneous reaction proceeds in the direction of ( s system + s environment) > 0.

The landlord is a middle school student That.

1) Metathesis reactions.

Generally, it depends on whether the reactant can be soluble in water or acid, and whether the product satisfies the precipitate or gas or water, and one of the three can be.

The product has the production of weak electrolytes, or simply "strong and weak".

2) Redox reactions.

See if there is a change in the valency of the reactants and products, that is, whether there are oxidants and reducing agents. There is also the oxidation of the oxidant is large and the oxidation product is the same as the replacement of the reducing agent The common ones are metal Activity order table k ba ca na mg al mn zn cr fe ni sn pb (h) cu hg ag pt au

At the middle school level, whether substances can react with each other is mainly analyzed from two perspectives: substance classification and redox. For example, sodium hydroxide can react with hydrochloric acid because acid has the universality of reacting with alkali, and alkali also has the universality of reacting with acid; Chlorine, sulfur dioxide and water can react because chlorine is very oxidizing, and sulfur dioxide has strong reducing properties, and redox reactions can occur between the two.

There are mainly redox reactions, metathesis reactions, hydrolysis-promoted reactions, complexation reactions, etc., and the complexation reactions that are exposed to in middle school are mainly the reactions of iron ions and thiocyanide ions, and the other three categories depend on the classification of substances and redox.

Generally refers to the reaction of gas, precipitation and water formation.

The textbook answer should be to observe if new substances are formed.

But I don't think that's what the landlord wants to ask.

Detect whether there is a change in physical and chemical properties.

Usually the properties of a mixture of two substances are different from those of a substance after a chemical reaction.

There are many ways to detect them, just look at the change in the mass of a chemical before and after its reaction.

See if the substance changes!

Whether a new substance has been produced.

To put it simply, it is to see whether there is precipitation, gas formation, whether the color and properties have changed, and whether there is a change in temperature.

The most fundamental thing is to check whether the original chemical properties of the substance have changed.

1) A metal element, B non-metal oxide.

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Whether or not to generate a new substance that exists steadily!