The steps of balancing chemical equations by fractional method are as follows:
(1) First, choose a more complicated chemical formula on the side where simple materials exists, assuming that the coefficient of this chemical formula is 1.
(2) Put an appropriate coefficient (which can be a fraction) before other chemical formulas to balance the number of atoms of other elements except elements.
(3) Then, put an appropriate coefficient (which can be a fraction) before the chemical formula of the simple substance to balance the atomic number of the simple substance.
(4) Finally, the coefficients before each chemical formula in the equation are expanded by appropriate multiples at the same time, and the denominator of each coefficient is removed to balance the chemical equation.
Example 1. Equilibrium chemical equation:
Analysis: the simple substance appears on one side of the reactant, and we assume that the coefficient is 1. Observe the number of C and H atoms on the left and right sides of the equation, put a coefficient 2 in front of it, and the coefficient in front of it 1 remains unchanged. At this time, the number of C and H atoms on the left and right sides has been balanced.
Then balance the number of o atoms. If the number of O atoms on the right side of the equation is 5, then a coefficient should be added in front of it.
Finally, remove the denominator. If the coefficient in front of each chemical formula in the equation is enlarged by 2 times at the same time, the chemical equation will be balanced.
Example 2. Equilibrium chemical equation
Analysis: simple materials appears on the side of the product. Assuming the coefficient is 1, the number of C and O atoms should be balanced first. Namely:
Then balance the number of iron atoms.
Finally, remove the denominator.
Note: For some simple materials reactions, especially the reaction between substances and oxygen, the fractional method can often make the chemical equation reach equilibrium quickly. However, the fractional method also has some limitations. Fractional method is more complicated and not applicable to the reactions in which there is no single substance in the reactants and products, or the complex reactions in which there are more than two reactants or products.
1 For the reaction of organic matter, look at the number in the lower right corner of H first, and the number of O for inorganic matter first, usually an odd number with 2. If it is not enough, it can be doubled.
2 the combustion of hydrocarbons, first look at h, c, and then look at o, its products are generally water and carbon dioxide.
If there is a common divisor, divide it by the simplest number.
4 charge balance, for the ion equation, except insoluble matter, gas and water, everything else is written in the form of ions, so (1) makes the charges at both ends of the equation equal.
(2) Observe the water-gas balance.
Some of them don't need pruning. Pay attention to the calculation first and then see if it needs pruning.
There are many ways to balance chemical equations:
1, observation method: This method often works for some simple equations. In fact, even if there is a purpose of making up numbers for balance, there are often factors such as parity. This method can be used for any type of equation.
2. Charge balance method: This method is most useful for ionic equation. In ionic equation, except insoluble matter, gas and water, everything is written in the form of ions. First, the charges at both ends of the equation are equal, and then the balance between water and gas is observed. This method generally won't fail. But it is too easy to be used in the redox equation.
3. Redox method: This method aims at the redox equation. Remember here: "When the valence increases, the redox agent is lost." Corresponding to this is that "reducing oxidant is obtained by reducing valence". The specific usage is:
(1) Mark the valence of the elements whose valence has changed at the top to distinguish who goes up and who goes down.
(2) Connect the same elements with lines to find out whether the number of charges increases or decreases.
(3) Find the least common multiple and multiply it by the number of increased or decreased charges respectively.
(4) Balance: Write the least common multiple of each multiplication operation before each chemical formula (i.e. coefficient). And pay attention to whether these elements with valence changes are equal before and after chemical changes. Generally speaking, if it is not equal, it is an integer multiple.
(5) Balance other substances such as water and generated insolubles by observation.
Balance method of chemical equation;
In the process of chemical change, we must follow the law of conservation of mass, that is, the number of elements before and after the reaction is equal to the number of atoms.
Common methods for balancing chemical equations are:
(1) Least common multiple method:
When balancing the chemical equation, observe the complex elements before and after the reaction, and then balance first. First, calculate the least common multiple of the atom of this element before and after the reaction, balance the atom by filling in the stoichiometric number before the chemical formula, and then observe the atomic numbers of other elements, so that the element types and atomic numbers of reactants and products in the chemical reaction are equal.
For example, the balance method introduced in the textbook is the least common multiple method. In the reaction of P+O2 ―― P2O5, oxygen is mixed first: the least common multiple is 10, the stoichiometric numbers are 5 and 2, and P+5O2 ―― 2P2O5; Then balance the phosphorus atoms, 4p+5o2 = = 2p2o5.
(2) Observation method:
A method of judging coordination stoichiometry by analyzing the chemical formula of a substance.
For example, equilibrium Fe2O3+Co-Fe+CO2. In the reaction, each CO combines with one oxygen atom to generate CO2 molecules, and Fe2O3 provides three oxygen atoms at a time, so three CO molecules must accept these three oxygen atoms to generate three CO2 molecules, that is, Fe2O3+3co-Fe+3co2, and finally the planar Fe2O3+3co = = 2fe+3co2 is obtained. This equilibrium method determines the chemical properties of CO by observing and analyzing the number of oxygen atoms in the chemical formula of Fe2O3.
(3) Method of changing odd numbers into even numbers:
The method of changing odd numbers into even numbers is called odd numbers into even numbers. The even elements in the chemical formula before and after the reaction are selected as the starting point for balancing, and then the atoms of other elements are balanced.
For example, to balance the combustion equation of methane (CH4), the method of changing odd numbers into even numbers can be adopted: CH4+O2-H2O+CO2. Before the reaction, the oxygen atoms in O2 were even, but after the reaction, the oxygen atoms in H2O were odd. First, the number of oxygen atoms is changed from odd to even: CH4+O2-2H2O+CO2, and then the atomic balance of other elements is CH4+2O2.
(4) Normalization method:
Find the key chemical formula in the chemical equation, set the stoichiometry before the chemical formula as 1, and then balance the stoichiometry before other chemical formulas according to the key chemical formula. If the measurement number is a fraction, then multiply each measurement number by the same integer to change the fraction into an integer. This equilibrium method of setting the measurement number of key chemical formula as 1 is called normalization method.
For example, this method can be used to balance the combustion chemical equation of methanol (CH3OH): CH3OH+O2 ―― H2O+CO2. Obviously, the key to determine the amount of H2O and CO2 is the composition of methanol, so the metering number is 1, so the molecular number of H2O and CO2 generated after combustion can be obtained: ch3oh+O2-2h2o+CO2. Then balance the oxygen atoms: ch3oh+3/2o2 = = 2h2o+CO2, multiply each measurement by 2 and divide it into integers: 2ch3oh+3o2 = = 4h2o+2co2.
It should be noted that no matter how to balance the chemical equation, only the stoichiometric number in front of the chemical formula can be changed, and the number in the lower right corner of the element in the chemical formula can never be changed. Because changing the number in the lower right corner of the element symbol means changing the composition of reactants and products, there may be substances that do not exist at all or reactants or products that have changed the original chemical changes, or there may be chemical changes that do not exist at all.
1 For the reaction of organic matter, look at the number in the lower right corner of H first, and the number of O for inorganic matter first, usually an odd number with 2. If it is not enough, it can be doubled.
2 the combustion of hydrocarbons, first look at h, c, and then look at o, its products are generally water and carbon dioxide.
If there is a common divisor, divide it by the simplest number.
4 charge balance, for the ion equation, except insoluble matter, gas and water, everything else is written in the form of ions, so (1) makes the charges at both ends of the equation equal.
(2) Observe the water-gas balance.
Some of them don't need pruning. Pay attention to the calculation first and then see if it needs pruning.
There are many ways to balance chemical equations:
1, observation method: This method often works for some simple equations. In fact, even if there is a purpose of making up numbers for balance, there are often factors such as parity. This method can be used for any type of equation.
2. Charge balance method: This method is most useful for ionic equation. In ionic equation, except insoluble matter, gas and water, everything is written in the form of ions. First, the charges at both ends of the equation are equal, and then the balance between water and gas is observed. This method generally won't fail. But it is too easy to be used in the redox equation.
3. Redox method: This method aims at the redox equation. Remember here: "When the valence increases, the redox agent is lost." Corresponding to this is that "reducing oxidant is obtained by reducing valence". The specific usage is:
(1) Mark the valence of the elements whose valence has changed at the top to distinguish who goes up and who goes down.
(2) Connect the same elements with lines to find out whether the number of charges increases or decreases.
(3) Find the least common multiple and multiply it by the number of increased or decreased charges respectively.
(4) Balance: Write the least common multiple of each multiplication operation before each chemical formula (i.e. coefficient). And pay attention to whether these elements with valence changes are equal before and after chemical changes. Generally speaking, if it is not equal, it is an integer multiple.
(5) Balance other substances such as water and generated insolubles by observation.
Balance method of chemical equation;
In the process of chemical change, we must follow the law of conservation of mass, that is, the number of elements before and after the reaction is equal to the number of atoms.
Common methods for balancing chemical equations are:
(1) Least common multiple method:
When balancing the chemical equation, observe the complex elements before and after the reaction, and then balance first. First, calculate the least common multiple of the atom of this element before and after the reaction, balance the atom by filling in the stoichiometric number before the chemical formula, and then observe the atomic numbers of other elements, so that the element types and atomic numbers of reactants and products in the chemical reaction are equal.
For example, the balance method introduced in the textbook is the least common multiple method. In the reaction of P+O2 ―― P2O5, oxygen is mixed first: the least common multiple is 10, the stoichiometric numbers are 5 and 2, and P+5O2 ―― 2P2O5; Then balance the phosphorus atoms, 4p+5o2 = = 2p2o5.
(2) Observation method:
A method of judging coordination stoichiometry by analyzing the chemical formula of a substance.
For example, equilibrium Fe2O3+Co-Fe+CO2. In the reaction, each CO combines with one oxygen atom to generate CO2 molecules, and Fe2O3 provides three oxygen atoms at a time, so three CO molecules must accept these three oxygen atoms to generate three CO2 molecules, that is, Fe2O3+3co-Fe+3co2, and finally the planar Fe2O3+3co = = 2fe+3co2 is obtained. This equilibrium method determines the chemical properties of CO by observing and analyzing the number of oxygen atoms in the chemical formula of Fe2O3.
(3) Method of changing odd numbers into even numbers:
The method of changing odd numbers into even numbers is called odd numbers into even numbers. The even elements in the chemical formula before and after the reaction are selected as the starting point for balancing, and then the atoms of other elements are balanced.
For example, to balance the combustion equation of methane (CH4), the method of changing odd numbers into even numbers can be adopted: CH4+O2-H2O+CO2. Before the reaction, the oxygen atoms in O2 were even, but after the reaction, the oxygen atoms in H2O were odd. First, the number of oxygen atoms is changed from odd to even: CH4+O2-2H2O+CO2, and then the atomic balance of other elements is CH4+2O2.
(4) Normalization method:
Find the key chemical formula in the chemical equation, set the stoichiometry before the chemical formula as 1, and then balance the stoichiometry before other chemical formulas according to the key chemical formula. If the measurement number is a fraction, then multiply each measurement number by the same integer to change the fraction into an integer. This equilibrium method of setting the measurement number of key chemical formula as 1 is called normalization method.
For example, this method can be used to balance the combustion chemical equation of methanol (CH3OH): CH3OH+O2 ―― H2O+CO2. Obviously, the key to determine the amount of H2O and CO2 is the composition of methanol, so the metering number is 1, so the molecular number of H2O and CO2 generated after combustion can be obtained: ch3oh+O2-2h2o+CO2. Then balance the oxygen atoms: ch3oh+3/2o2 = = 2h2o+CO2, multiply each measurement by 2 and divide it into integers: 2ch3oh+3o2 = = 4h2o+2co2.
It should be noted that no matter how to balance the chemical equation, only the stoichiometric number in front of the chemical formula can be changed, and the number in the lower right corner of the element in the chemical formula can never be changed. Because changing the number in the lower right corner of the element symbol means changing the composition of reactants and products, there may be substances that do not exist at all or reactants or products that have changed the original chemical changes, or there may be chemical changes that do not exist at all.
The balance of chemical equations is an important content and a difficult point. The commonly used methods of junior middle school chemistry equation are observation method, least common multiple method, odd spouse method and so on. Next, another method of balancing chemical equations-fractional method is introduced.
The steps of balancing chemical equations by fractional method are as follows:
(1) First, choose a more complicated chemical formula on the side where simple materials exists, assuming that the coefficient of this chemical formula is 1.
(2) Put an appropriate coefficient (which can be a fraction) before other chemical formulas to balance the number of atoms of other elements except elements.
(3) Then, put an appropriate coefficient (which can be a fraction) before the chemical formula of the simple substance to balance the atomic number of the simple substance.
(4) Finally, the coefficients before each chemical formula in the equation are expanded by appropriate multiples at the same time, and the coefficients are removed.