What is the Difference Method? How to use?? Let s talk about a detailed example problem!

The difference method is based on the change in the quantity of a substance before and after the chemical change, and finds the so-called "theoretical difference". The difference mainly includes: the difference in quality, the difference in the quantity of the substance, the difference in the volume of the gas, the difference in pressure, the difference in heat in the reaction process, etc.

This difference is proportional to the corresponding quantity of the substance in the chemical equation, and the difference method is to solve the calculation problem of a certain quantity change with the help of this proportional relationship. The key to solving this type of problem is to determine the "theoretical difference" according to the meaning of the question, and then list the proportional formula according to the "actual difference" provided by the question, and then solve it. The key to solving the problem is to be able to correctly find the "theoretical difference" corresponding to the "actual difference" in the problem from the reaction equation.

In the calculation according to chemical equations, sometimes the problem gives the condition not the mass of a certain reactant or product, but the difference between the mass of the substance before and after the reaction. The key to this method is to analyze the causes of the difference before and after the reaction (i.e., the factors affecting the change of mass) according to the chemical equation, find out the relationship between the difference and the known quantity and the unknown quantity, and then solve it in a proportional formula.

You can take a look at this example.

It seems that there is only the spread method in mathematics. Isn't the difference method in chemistry?

Variance analysis is a method that analyzes the difference revenue and cost between alternatives, and makes a selection based on the difference profit.

The process of comparing and selecting different options is essentially the process of selecting the plan with the greatest benefit, and the maximum benefit is generated in the comparison of the income and cost of each alternative. When two alternatives have different expected revenues and expected costs, the method of selecting the optimal solution based on the difference income between the two alternatives and the difference profit and loss calculated by the difference cost is called the difference analysis method.

Difference analysis.

In decision analysis, the variance refers to the difference between different alternatives, which in turn is divided into the difference revenue, the cost of the difference, and the profit of the difference. Variance analysis refers to the method of selecting the optimal solution based on a full analysis of the variance income, variance cost and differential profit of different alternatives.

The general steps of a difference analysis are four steps:

1. Calculate the difference income of the alternatives;

2. Calculate the cost of the difference of the alternatives;

3. Calculate the difference profit of the alternatives;

4. Compare the optimal scheme.

There are two types of factors in the difference analysis method.

Differential income. Variance income is the difference between the expected income of one option and the expected income of another option.

Differential cost. Variance cost is the difference between the expected cost of one alternative and the expected cost of another.

If the difference income is greater than the difference cost, that is, the difference profit and loss is positive, the former option is preferred; Conversely, if the difference income is less than the difference cost, that is, the difference profit and loss is negative, the latter option is preferable.

For example, if an enterprise is faced with the decision of which product to produce, the unit variable cost of product A is 80 yuan, the estimated sales volume is 1000 pieces, and the estimated sales unit price is 110 yuan; The unit variable cost of production B is 220 yuan, the estimated sales volume is 500 pieces, and the estimated sales unit price is 260 yuan. The fixed costs for the production of products A and B are the same. then the production of product A and the production of product B:

Difference income = (110 yuan 1000) - (260 yuan 500) = -20000 yuan.

Difference cost = (80 yuan 1000) - (220 yuan 500) = -30000 yuan.

Difference profit and loss = (-20,000 yuan) - (30,000 yuan) = 10,000 yuan, indicating that the production of product A can obtain 10 000 yuan more profit than the production of product B, and the production of product A is beneficial to the enterprise.

1. Difference method.

The differential method is based on chemical reactions.

Certain changes before and after find out the so-called theoretical difference (difference in the mass of the solid, difference in the mass of the solution, difference in the volume of the gas, quantity of the gaseous substance.

is a method of solving a problem that is proportional to the amount of change in the reaction or product. This method treats the "difference" as a chemical equation.

The one at the right end is to list the known difference (actual difference) in proportion to the corresponding difference (theoretical difference) in the chemical equation, and the other steps to solve the problem are exactly the same as according to the proportion of the chemical bridge equation or solve the problem.

Example 1: Put a small piece of Na into 50GFeCl3 solution, and after the reaction is complete, filter it to obtain a solution that still has a brownish yellow color, and the mass of the Na put in is.

a. Poor slag pie.

B, C, D, analytical]Na was put into FeCl3 solution and the following reaction occurred.

6na+2fecl3+6h2o=6nacl+2fe(oh)3↓+3h2↑

If 2molFeCl3 reacts with 6molH2O, 6mol NaCl is generated, and the mass of the solution is reduced by 82g, and the Na participating in the reaction is 6mol.

Now that the mass of the solution is reduced, the Na participating in the reaction should be, and the mass should be. The answer is (c).

For example, under the same temperature and pressure, a bottle is filled with O2 and weighs 116g, when it is filled with CO2, it weighs 122g, and when it is filled with a certain gas, it weighs 114g, then the relative molecular weight of the gas.

for (a, 28

b、60c、32

d, 14 analysis].

From "at the same temperature, pressure and volume, the mass ratio of different gases is equal to their molar mass ratio", it can be seen that in this problem, the difference between the mass of the gas is directly proportional to the difference in the quantity. Therefore, the mass of this bottle can be solved directly by the proportional formula without calculating the mass of the bottle

122-116) (44-32) = (122-114) (44-m (gas)).

Applicable conditions for the difference method:

1) The reaction is incomplete or there are residues. In this case, the difference reflects the reaction that actually occurred, eliminating the influence of the unreacted species on the calculation, allowing the calculation to proceed smoothly. (For example, if the iron sheet is added to a copper sulfate solution, and the mass of the iron sheet is weighed after 10min, we can calculate the mass of Fe participating in the reaction according to the difference).

2) There is a difference before and after the reaction, and this difference is easy to find. This is a prerequisite for the use of the difference method. It is only when the difference is easy to find that the difference method is fast, otherwise, other methods should be considered.

3) The formula of the slip elimination method is: fractional difference and actual difference.

The difference method is based on the fact that certain "differences" (difference in solid mass, solution quality, gas volume, gaseous substance, etc.) before and after a chemical reaction are proportional to the amount of change in reactants or products. In this method, the "difference" is regarded as one of the right ends of the chemical equation, and the known difference (the actual difference) is proportional to the corresponding difference (theoretical difference) in the chemical equation, and the other steps are exactly the same as the proportional solution of the chemical equation. The key to solving the problem with the difference method is to find the theoretical difference correctly.

The difference method is based on the chemical equation, using the proportional relationship between the mass difference of the substance before and after the chemical change and any quantity in the equation, and using the difference as a breakthrough to solve the problem.

Example 1 Put a small piece of iron in dilute sulfuric acid, after the iron block is completely reacted, the mass of the solution is weighed to be 100g, and how many grams of iron is put in before the reaction? How many grams of hydrogen are produced?

Fe + H2SO4 = FeSO4 + H2 difference.

y 100g－

x = g y = g.

For example, if you weigh a bottle of drink before you drink it and weigh it again after a few sips, the difference between the two weights is the weight you drink. This is the difference method.

Insert the iron sheet into the copper sulfate solution, take out the iron sheet after a while, dry and weigh it, and find that the mass of the iron sheet increases grams, how much iron reacts?

fe+cuso4=feso4+cu

56 64 Mass increase 64-56=8

x Mass increases grams.

x = 56 * grams, with iron reaction.