What is the trimming of chemical equations, and the balancing of chemical equations

Chemical equation.

It is a formula in which the equation is equal to the left (or arrow) of each reactant and the right is the chemical formula of each product. For example, hydrogen and oxygen react to produce water

h2+o2=h2o。Equation trimming means that the chemical equation is conserved by atoms, and in the equation on the left, the reactant has two oxygen atoms.

But there is only one on the right, so in order to trim the equation.

It is necessary to match the coefficient before each substance. The end result is 2H2+O2=2H2O.

It is to add a number in front of the molecule, so that the number of atoms on both sides is multiplied by this number, and the number of atoms on both sides is the same!

If you still don't understand Example:

2hg+o2＝2hgo

Original chemical formula. hg+o2→hgo

Then add 2 before hg, which means two hg atoms.

Add a 2 before hgo, which is two hg and two o atoms.

O2 is also two O atoms, so there are two O atoms on both sides.

There are also two Hg atoms on both sides.

So the number of various atoms that both sides have is equal.

Adding the corresponding number to the chemical equation is called trimming.

Because the law of conservation of mass is to be followed.

A few examples of trim should be understood.

a) Least common multiple method.

This method is suitable for common chemical equations that are not too 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↑

2) Odd-even equalization.

This method is suitable for multiple occurrences of an element on both sides of the chemical equation, and 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 other molecular coefficients appear as fractions, it can be matched with 4), from which it can be deduced that the first 2 of C2H2 becomes: 2C2H2+O2==CO2+2H2O, from which it can be seen that the coefficient before CO2 should be 4, and the final coefficients with elemental O2 are 5, and the conditions can be specified:

2c2h2+5o2==4co2+2h2o

c) Observational 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, Fe3O4 Fe** 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 This deduces that the H2 coefficient is 4, indicating the conditions, ** Change to an equal sign:

3fe+4h2o==fe3o4+4h2↑

Uplink: 38324 Downlink: 14122 is the measurement number of the reaction between copper and concentrated nitric acid and the reaction of dilute nitric acid. The specific analysis is as follows:

Uplink: 38324:

3Cu + 8Hno3 (dilute) = 3Cu (NO3) 2 + 2No + 4H2O38324 is the balancing coefficient of the reaction between dilute nitric acid and copper.

Downlink: 14122:

Cu + 4Hno3 (concentrated) = Cu (No3) 2 + 2 No2 + 2H2O14122 is the balance coefficient of the reaction between concentrated nitric acid and copper.

The chemical reaction equation strictly adheres to the law of conservation of mass, and after writing the chemical reaction equation and writing the reactants and products, the number of atoms on the left and right sides is often not equal, and the law of conservation of mass is not satisfied, which needs to be solved by calculating the balance.

For example, "Na+H2O=Naoh+H2"; Method 1: Parity Trim Method, which is suitable for multiple occurrences of an element on both sides of a chemical equation, and the total number of atoms of the element on both sides is odd and even.

The hydrogen atom is matched first, there are two hydrogen atoms on the left, and there is only one hydrogen atom on the right Naoh, there are two hydrogen atoms in the hydrogen, and the total number of hydrogen atoms should be even, so the coefficient before NaOH is 2, and the number of oxygen atoms on the right is 2, and so on, the coefficient before H2O is 2, and the coefficient before NaOH is also 2.

Electron gain and loss method: find the oxidant and reducing agent from the reaction formula, and show the change in the valency of the oxidized element or reducing element before and after the reaction, so as to determine the number of electron gain and loss.

Sodium loses one electron and the hydrogen atom gains two electrons, so the coefficient before sodium is 2, and according to the law of conservation of mass, the coefficient of NaOH and H2O is 2.

I'll give you oneUniversal balancing, inThere is nothing wrong with the equation elementswhen encounteredThe number of elements varies by an odd numberThe love of the dry grip attack,That is, it is not divisible by twoThe coefficient is replaced by a fractionAfter the equal coefficients are flat, multiply each coefficient by the denominator of the fractional coefficient。IfThe question has already been assigned to you with a partial flat, if soEven numberUse the fractional method just now, if soOdd numberThen multiply the odd coefficient by two, if the result does not need to be divided, there is no need to move, if it is required, it is divided.

The chemical reaction equation strictly adheres to the law of conservation of mass, and after writing the chemical reaction equation and writing the reactants and products, the number of atoms on the left and right sides is often not equal, and the law of conservation of mass is not satisfied, which needs to be solved by trimming.

Usually, the equation equals sign is written in the exam equalization question, and the candidate needs to change the ** to the equals, otherwise there will be no points.

For example, KCro - KCl+O, after trimming, ** should be changed to an equal sign 2KCLO ==2KCL+3O, and there are three things that need to be done to balance the chemical equation

1. The trim coefficient, the coefficient of each chemical formula in the trim chemical equation, and the coefficient 1 in some places cannot be omitted;

2. Change the single line to a double line, which is easy to ignore in the chemical equation;

3. The gas or precipitate needs to have an up or down arrow.

Equalize the number of atoms on both sides of the equal sign.

It should be matched according to the conservation of electrons.

3S + 4HNO3 --3SO2 + 4NO + 2H2O2Fe + 6H2SO4 (hot, concentrated) -Fe2(SO4)3 + 3SO2 + 6H2O

zn + nh4no3 --zno + n2 + 2h2o2fe(oh)2 + cl2 + 2oh- -2fe(oh)3 + 2cl-

2mno4- +5no2- +6h+ -2mn2+ +5no3- +3h2o

2na2o2 + 2co2 --2na2co3 + o2

Redox reactions are conserved according to the gains and losses of electrons.

The first 3 4 3 4 2

The second 2 6 1 3 6