High School Chemistry Equation Trimming, High School Chemistry Equation Trimming Techniques

Conservation of electric charge. Manganese changes from 7-valent to 2-valent, giving five electrons. The oxygen in hydrogen peroxide changes from negative 1 valence to 0 valence oxygen, losing two electrons.

It is these two things that have the charge moving in the system. Because the number of electrons gained is equal to the number of electrons lost, there are two permanganate groups and five hydrogen peroxides. Manganese ions are made from permanganate, so there are two manganese ions, and oxygen is from hydrogen peroxide, so there are five oxygens.

Further back is the leveling water. As mentioned earlier, there are 2*4=8 oxygen atoms in manganate, and hydrogen peroxide provides 5*2=10 hydrogen ions. It takes 6 hydrogen ions to get exactly 8 water.

2mno4- +5h2o2 +6h+=2mn2+ +5o2 +8h2o

The manganese in mnO4- is reduced from +7 valence to +2 valence of Mn2+, giving 5 electrons; The oxygen in H2O2 rises from -1 valence to 0 valence of O2 and loses 2 electrons. So mno4 - preceded by 2; H2O2 is preceded by 5, and the other cases are just balanced by atomic numbers.

MNO4- is +7 in MNO4- and is reduced to MN2+ to give 5 electrons.

In H2O2, O is -1, which is oxidized to give O2 and loses 1 electron 2 (because an oxygen molecule is made up of two oxygen atoms).

i.e.: mno4- ===> mN2+ gives 5e

H2O2 ===> O2, lose 2E

So, the common multiple of 5 and 2 is 10, so the mno4- coefficient is 2 and the H2O2 coefficient is 5

First, we get: 2mNO4- +5H2O2 + H+ -2MN2+ +5O2 + H2O

Then, observe how many o's are left.

Before the reaction, there were a total of 2 4 + 5 2 o = 18

After the reaction, it is 5 O2, and 10 O's are used, so there are still 18-10=8 O's in H2O.

So, the coefficient of h+ is h + xh+ == 8 h in 5 h2o2 h===> x=6

And finally. 2mNO4- +5H2O2 + 6H+ ===2mn2+ +5O2 + 8 H2O

The ascending conservation mno4 is multiplied by 2 H2O2 by 5

Atoms are conserved Mn2- times 2 O2 times 5

And then the conservation of electrons is 4 on the right and 2 on the left -- and 6 is added

Finally, the oxygen atom is conserved.

Well, this one seems a bit weird.

High School Chemistry Equation Trim Tips:

1. Establish a 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.

2. Least common multiple method.

This method is suitable for common chemical equations that are not too difficult. For example, if the number of oxygen atoms on the right is 2 and 3 on the left, then the least common multiple is 6.

Therefore, the coefficient before KCLO3 should be matched with 2, and O2 should be matched with 3, and the formula becomes: 2KCLO3 KCl+3O2, because the number of potassium atoms and chlorine atoms on the left becomes 2, then the coefficient before KCL should be matched with 2, ** is changed to equal sign, and the condition is marked, that is: 2KCLO3==2KCL+3O2

3. Odd-even matching.

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.

The balance of this equation starts with the oxygen atom that appears the most first. 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.

4. Conservation method of total electronic gains and losses.

This method is the most common method and its basic balancing steps are described in textbooks. Here are some tips for this matching.

For some of the more complex redox reactions, such as changes in the valency of multiple elements in a substance, the substance can be considered as a whole.

In the case of redox reactions, the reaction is first conserved according to the gain and loss of electrons, and then according to the number of atoms.

1 marked valence state, 2 column changes, 3 find the least common multiple 4 use observation method to balance the gain and loss of electrons, the number of atoms, and the charge must be conserved.

Example C + 2H2SO4 = CO2 + 2SO2+ H2O

4e*1 +2e*2

It is necessary to mark the changed valency first, and see the loss of electrons.

Multiply by as much as you want, and then use the observation method to match.

Trim method for chemical equations high school:

1. Zero-price method.

Usage: It is impossible to determine that each element in the valency of a substance with valence is zero valence by conventional methods, and then calculate the rise and fall value of each element, and make the valence rise and fall value of the elements equal, and finally use the observation method to balance the stoichiometric numbers of other substances.

2. Average price method.

Usage: When the atoms of the same element in the same reactant appear twice and the valence states are different, they can be treated equally, that is, assuming that their valency is the same, the average price is marked according to the principle of zero valency algebra in the compound, and if the equation appears diatomic molecule, the number of atoms should be increased by 2 times.

Usage: When there are several atoms or clusters of atoms of an element (mostly seen in organic reaction trimming) in a compound, it can be treated as a whole and priced as a whole according to the principle of algebraic sum of the valency of the elements in the compound.

4. Reverse trim method.

If the valency of an element in the oxidant (or reducing agent) is only partially changed, the balancing should start from the oxidation product and the reduction product, that is, the product should be considered first, and the trim should be reversed; For the equation of self-redox reaction, it is advisable to start balancing from the product, that is, reverse balancing.

5. Trim method for organic reactions.

In the redox reaction in which organic matter is involved, the first thing is to specify that h is 1 valence and o is 2 valence in organic matter, and the average valency of carbon is determined by this. Then, according to the principle that the total number of reducing agent valence increases and the total number of oxidant valence decreases are equal, the balance is combined with the observation method.

6. Trimming of the missing equation.

If there are reactants or products in the given chemical equation that are not written, in the time of matching, if the vacant substance does not gain or lose electrons, but only provides an acid, alkali, and neutral environment for reaction, you can first balance the elements with valency and rise, and then determine the missing substance, and fill in the coefficient.

Observational method. It is directly by observing reactants and products, and balancing according to the law of conservation of mass and the law of conservation of atoms.

Valence lifting method.

This method is suitable for the balancing of redox reaction equations. Which element in the reactant increases its valence and which element decreases its valence is marked first, and then balanced according to the conservation of electrons.

Trim the redox reaction equation with the ionic-electron method.

In addition to the valency rise and fall method for redox reactions in aqueous solution, ion-electron method is generally commonly used for leveling. The distribution plain is that the total number of electrons gained by the oxidant during the reaction is equal to the total number of electrons lost by the reducing agent.

Now illustrate the trim steps with the following example.

In an acidic medium, KMno4 reacts with K2SO3 to form MnSO4 and K2SO4, which are balanced by this chemical equation.

The specific steps for trimming are as follows:

1) Write the unbalanced ion equation according to the reaction.

2) Write two semi-reactive formulas, one for the reaction in which the reducing agent is oxidized and the other for the reaction in which the oxidant is reduced:

The number of oxygen atoms in the product is more than that in the reactant, and the reaction is carried out in an acidic medium, so H2O can be added to the reactant in the above formula, H+ is added to the product, and then the balance of the atomic number and charge number of each element can be obtained

In the formula, the number of oxygen atoms in the product decreases, and enough hydrogen ions (2 times the number of oxygen atoms decreased) should be added to make it combine into water, and after trimming, it gets:

3) According to the principle of equal number of electrons gained and lost by the oxidant and reducing agent, multiply by the appropriate coefficient in each of the two half-reactive equations, i.e., 5, 2, and then add them to obtain a balanced ion equation:

4) Write the complete reaction equation:

5k2so3+2kmno4+3h2so4=6k2so4+2mnso4+3h2o

Valence rise and fall method is a method that has a wide range of applications for leveling redox reaction equations. Although the ionic-electronic method is only suitable for the trimming of the ionic equation in solution, it avoids the calculation of valence. The more complex redox reactions carried out in aqueous solutions are generally leveled by the ion-electron method.

These two trimming methods can complement each other.

Example: 2H2O2 = (Mno2) = 2H2O + O2 (arrow) where the valency of H is unchanged What changes is O, O in O2 loses electrons and the valency increases; O in H2O gets electrons, and the valency decreases. So the number of valence atoms is 4.

Trim is based on the change in valency of the elements before and after the reflection. First, if there is a change in valency, the electrons that change before and after are conserved, and then the others are balanced according to the conservation of atoms.

For example, HCL and MNO2 are used to produce Cl2

1 Write the reaction formula HCl+MNO2=(condition)=Cl2+mnCl2+H2O (you can write Cl2 first, and then add it).

2 Find the element of valence Cl loses electrons, then Mn gains electrons and equalizes according to the number of electrons gained.

2hcl2+mno2==cl2+mn2+

3 According to the conservation of atoms, the balance of the atom without valence has H and O, generally produces H2O4HCl+Mno2==Cl2+MnCl2+2H2O, and finally there is a gas precipitated with arrows.

If it's a high school chemistry equation, it depends on how difficult it is, and there are chemical equations in the book that you can memorize special ones, for example, whether the reaction between metal and nitric acid depends on whether it's one to four or three to eight, and then you can memorize a few special parameter calculations, just like the equation for the oxidation of iron hydroxide in the air, and you can memorize the previous one by remembering the factor of four for ferric hydroxide.

It's rare to have no contact poured.

Just use the equation for redox reactions, use the electron transfer and the rise and fall of the valence, use the number of electrons gained and lost to be equal, and the valency rise and fall are equal, or if there are two iron atoms in front of the equation, then add a two in front of the iron atom in front of the next iron atom, and then use the above method.

For the redox reaction, first find out the oxidant reducing agent (or oxidation product reduction product), and then according to the principle of "valence rise and fall conservation", determine the coefficient ratio of the oxidant reducing agent (or oxidation product reduction product), and then obtain the coefficient of the oxidation product reduction product (or oxidant reducing agent), and the rest of the substances are determined according to the conservation of elements.

Use the observation method first, and then gain and lose the conservation of electrons,。。

Number of electrons lost = number of electrons gained.