How to match the law of conservation of mass

Chemical Equation Balancing: The equation of chemical reactions strictly adheres to the law of conservation of mass.

There are two kinds. The formulation of redox reaction (valency change): the price of the reactant that increases or decreases the amount of the element (that is, 2 for example, O2 is taken later), and then calculate the amount of each element, and then write the coefficient on the other side according to this.

If not, it's simpler, according to the atomic cluster, because the atomic cluster is constant, so just write the number of each atomic cluster in each type, and then take the least common multiple.

There are many ways to do this. The simpler ones are the least common multiple method and the observation method.

1.The least common multiple method is the ordinary odd and even number method, after the chemical equation is correctly written, see if each chemical formula is a coefficient, and then according to the least common multiple of mathematics.

2.Our teacher is talking about the "meow method", and after writing the chemical equation, observe it carefully.

a The trimming of chemical equations is to comply with the law of conservation of mass.

That's right; b Trim the chemical equation, can not change the chemical formula of the substance, that is, change the number in the lower right corner of each constituent element in the chemical formula, wrong;

c in certain chemical reactions.

Medium atoms can be redivided, such as calcined calcium carbonate at high temperatures.

Therefore it is wrong; d If there is gas in the reactant, the gas product does not need to be marked with the "" sign, so it is wrong to choose A

The equation of chemical reaction strictly abides by the law of conservation of mass.

Test Topic: Trimming of Chemical Equations Topic: Chemical Terminology and the Law of Conservation of Mass Analysis:

According to the written chemical equation to comply with the law of conservation of mass, the type and number of atoms on both sides of the equal sign must be equal, analysis and solution Chemical reactions exist objectively, and chemical equations reflect the objective facts of chemical reactions, so there are two principles to pay attention to when writing chemical equations: first, it must be based on objective facts, and it is absolutely impossible to conjecture and fabricate substances and chemical reactions that do not actually exist; Second, to abide by the law of conservation of mass, the type and number of atoms on both sides of the equal sign must be equal; Therefore, when leveling the chemical equation, the basis for whether the stoichiometric number is correct is whether the number of atoms of various elements is equal Therefore, d is selected:d Comments:

This question is not very difficult, and you can answer this question correctly by mastering the law of conservation of mass in order to abide by the law of conservation of mass in writing chemical equations

Trim is the same as the elements on the left and right sides of the equation, if there are 5 carbon atoms on the left, then there must be 5 carbon atoms on the right side as well. In a chemical reaction, the sum of the masses of each substance before participating in the reaction is equal to the sum of the masses of the substances produced after the reaction. This law is called the law of conservation of mass.

a) Least common multiple method This method is suitable for common chemical equations that are not very difficult. For example, in this reaction formula, the number of oxygen atoms on the right is 2, and the number of oxygen atoms on the left is 3, then the least common multiple is 6, so the coefficient before kclo3 should be matched with 2, and the coefficient before O2 should be matched with 3, and the formula becomes: 2kclo3 KCl+3O2, since the number of potassium atoms and chlorine atoms on the left becomes 2, then the coefficient 2 before KCL, ** is changed to equal sign, indicating the condition is:

2kclo3==2kcl+3o2 [this paragraph] (2) odd-even balancing method.

This method is suitable for multiple occurrences of an element on both sides of a chemical equation where the total number of atoms of the element on both sides is odd and even, for example: C2H2+O2 CO2+H2O, and the balance of this equation starts with the oxygen atom with the highest number of occurrences. There are 2 oxygen atoms in O2, and the total number of oxygen atoms should be even, regardless of the number of coefficients before the chemical formula.

Therefore, the coefficient of H2O on the right should be matched with 2 (if the molecular coefficient of its Qingyu vertical appears as a fraction, it can be matched with 4), from which it is deduced that the first 2 of Dazhi C2H2, the formula becomes: 2C2H2+O2 CO2+2H2O, from which it can be seen that the coefficient before CO2 should be 4, and the final coefficient of elemental O2 is 5

2C2H2+5O2==4CO2+2H2O [this paragraph] (3) Observation balancing Sometimes there will be a substance with a more complex chemical formula in the equation, we can deduce the coefficients of other chemical formulas through this complex molecule, for example: Fe + H2O Fe3O4 + H2, Fe3O4 chemical formula is more complex, obviously, Fe ** in Fe3O4 is in the elemental Fe, O comes from H2O, then Fe is preceded by 3, H2O is preceded by 4, then the formula is: 3Fe + 4H2O FE3O4+H2 thus deduces that the H2 coefficient is 4, and the conditions are specified, and ** can be changed to an equal sign:

3fe+4h2o==fe3o4+4h2

Note: In the chemical equation of this entry, the ones that are not in bold are the foot markers. In this experiment, H2O must be gaseous, so H2 is not superscripted.

4) Normalization Law:

Find the key chemical formula in the chemical equation, set the number before the chemical formula as 1, and then balance the number before the other chemical formulas according to the key chemical formula. If the measured number is a fraction, and then the measured number is multiplied by the same integer, and the fraction is turned into an integer, this balancing method in which the key chemical formula measurement number is 1 is predetermined, which is called the normalization method. Method:

Select the most complex chemical formula in the chemical equation, let its coefficient be 1, and then extrapolate in turn.

Step 1: Let the coefficient of NH3 be 1 1NH3+O2 - NO+H2O

Step 2: The N and H atoms in the reaction are transferred to No and H2O respectively, by.

Step 3: Push the O2 coefficient from the total number of oxygen atoms at the right end.

That is, the number of the same atoms before and after the reaction should be the same.