Chemical reactions occur at different rates. Some of them are completely completed in small fractions of a second, others are carried out in minutes, hours, days; reactions are known that require several years to occur. In addition, the same reaction can, under the same conditions, for example, with elevated temperatures, proceed quickly, but in others, for example, during cooling, slowly; Moreover, the difference in the speed of the same reaction can be very large.

When considering the rate of a chemical reaction, it is necessary to distinguish between reactions occurring in a homogeneous system (homogeneous reactions) and reactions occurring in a heterogeneous system (heterogeneous reactions).

DEFINITION

System in chemistry it is customary to call the substance or collection of substances in question. In this case, the system is opposed external environment- substances surrounding the system.

There are homogeneous and heterogeneous systems. Homogeneous a system consisting of one phase is called heterogeneous- a system consisting of several phases. Phase is a part of a system separated from its other parts by an interface, during the transition through which the properties change abruptly.

An example of a homogeneous system is any gas mixture 9all gases at not very high pressures dissolve indefinitely in each other) or a solution of several substances in one solvent.

Examples of heterogeneous systems include the following systems: water with ice, a saturated solution with sediment, coal and sulfur in an air atmosphere.

If a reaction occurs in a homogeneous system, then it occurs throughout the entire volume of this system. If a reaction occurs between substances forming a heterogeneous system, then it can only occur at the interface between the phases forming the system. In this regard, the rate of a homogeneous reaction and the rate of a heterogeneous reaction are defined differently.

DEFINITION

Speed of homogeneous reaction is the amount of a substance that reacts or is formed during a reaction per unit time per unit volume of the system.

Speed of heterogeneous reaction is the amount of substance that reacts or is formed during a reaction per unit time per unit surface area of the phase.

Both of these definitions can be written in mathematical form. Let us introduce the following notation: υ homogen - reaction rate in a homogeneous system; υ h etero gen - reaction rate in a heterogeneous system; n - number of moles of any of the substances resulting from the reaction; V is the volume of the system; t-time; S is the surface area of the phase on which the reaction occurs; Δ - sign of increment (Δn = n 2 -n 1; Δt = t 2 -t 1). Then

υ homogen = Δn / (V× Δt);

υ heterogen = Δn / (S× Δt).

The first of these equations can be simplified. The ratio of the amount of a substance (n) to the volume (V) of the system is the molar concentration (c) of the substance: c=n/V, from where Δc=Δn/V and finally:

υ homogene = Δc / Δt.

Examples of problem solving

EXAMPLE 1

Exercise

Make up the formulas of two iron oxides if the mass fractions of iron in them are 77.8% and 70.0%.

Solution

Let's find the mass fraction in each of the copper oxides:

ω 1 (O) = 100% - ω 1 (Fe) = 100% - 77.8% = 22.2%;

ω 2 (O) = 100% - ω 2 (Fe) = 100% - 70.0% = 30.0%.

Let us denote the number of moles of elements included in the compound by “x” (iron) and “y” (oxygen). Then, the molar ratio will look like this (values of relative atomic masses taken from periodic table DI. Mendeleev rounded to whole numbers):

x:y = ω 1 (Fe)/Ar(Fe) : ω 1 (O)/Ar(O);

x:y = 77.8/56: 22.2/16;

x:y = 1.39: 1.39 = 1:1.

This means that the formula of the first iron oxide will be FeO.

x:y = ω 2 (Fe)/Ar(Fe) : ω 2 (O)/Ar(O);

x:y = 70/56: 30/16;

x:y = 1.25: 1.875 = 1: 1.5 = 2: 3.

This means that the formula of the second iron oxide will be Fe 2 O 3.

Answer

FeO, Fe2O3

EXAMPLE 2

Exercise

Write a formula for the compound of hydrogen, iodine and oxygen if the mass fractions of the elements in it are: ω(H) = 2.2%, ω(I) = 55.7%, ω(O) = 42.1%.

Solution

The mass fraction of element X in a molecule of the composition NX is calculated using the following formula:

ω (X) = n × Ar (X) / M (HX) × 100%.

Let us denote the number of moles of elements included in the compound as “x” (hydrogen), “y” (iodine), “z” (oxygen). Then, the molar ratio will look like this (the values of relative atomic masses taken from D.I. Mendeleev’s Periodic Table are rounded to whole numbers):

x:y:z = ω(H)/Ar(H) : ω(I)/Ar(I) : ω(O)/Ar(O);

x:y:z= 2.2/1: 55.7/127: 42.1/16;

x:y:z= 2.2: 0.44: 2.63 = 5: 1: 6.

This means that the formula for the compound of hydrogen, iodine and oxygen will be H 5 IO 6 .

Answer

H5IO6

Some chemical reactions occur almost instantly (explosion of an oxygen-hydrogen mixture, ion exchange reactions in an aqueous solution), others quickly (combustion of substances, interaction of zinc with acid), and others slowly (rusting of iron, rotting of organic residues). Reactions are known to be so slow that a person simply cannot notice them. For example, the transformation of granite into sand and clay occurs over thousands of years.

In other words, chemical reactions can occur with different speed.

But what is it speed reaction? What's it like precise definition of a given quantity and, most importantly, its mathematical expression?

The rate of a reaction is the change in the amount of a substance per unit of time in one unit of volume. Mathematically, this expression is written as:

Where n 1 Andn 2 – amount of substance (mol) at time t 1 and t 2, respectively, in a system of volume V.

Which plus or minus sign (±) will appear in front of the speed expression depends on whether we are looking at a change in the amount of a substance - a product or a reactant.

Obviously, during the reaction, reagents are consumed, that is, their quantity decreases, therefore, for reagents, the expression (n 2 - n 1) always has a value less than zero. Since speed cannot be a negative value, in this case you need to put a minus sign in front of the expression.

If we look at the change in the amount of the product, and not the reactant, then the minus sign is not required before the expression for calculating the speed, since the expression (n 2 - n 1) in this case is always positive, because the amount of product as a result of the reaction can only increase.

Substance quantity ratio n to the volume in which this amount of substance is located is called molar concentration WITH:

Thus, using the concept of molar concentration and its mathematical expression, we can write another option for determining the reaction rate:

The reaction rate is the change in the molar concentration of a substance as a result of a chemical reaction in one unit of time:

Factors affecting reaction speed

It is often extremely important to know what determines the speed of a particular reaction and how to influence it. For example, the oil refining industry literally fights for every additional half a percent of product per unit of time. After all, given the huge amount of oil processed, even half a percent results in a large financial annual profit. In some cases, it is extremely important to slow down some reaction, in particular the corrosion of metals.

So what does the reaction rate depend on? It depends, oddly enough, on many different parameters.

In order to understand this issue, first of all, let's imagine what happens as a result of a chemical reaction, for example:

A + B → C + D

The equation written above reflects the process in which molecules of substances A and B, colliding with each other, form molecules of substances C and D.

That is, undoubtedly, in order for the reaction to take place, at a minimum, a collision of the molecules of the starting substances is necessary. Obviously, if we increase the number of molecules per unit volume, the number of collisions will increase in the same way that the frequency of your collisions with passengers on a crowded bus will increase compared to a half-empty one.

In other words, the reaction rate increases with increasing concentration of reactants.

In the case where one or more of the reactants are gases, the reaction rate increases with increasing pressure, since the pressure of a gas is always directly proportional to the concentration of its constituent molecules.

However, the collision of particles is a necessary, but not at all sufficient condition for the reaction to occur. The fact is that, according to calculations, the number of collisions of molecules of reacting substances at their reasonable concentration is so great that all reactions must occur in an instant. However, in practice this does not happen. What's the matter?

The fact is that not every collision of reactant molecules will necessarily be effective. Many collisions are elastic—the molecules bounce off each other like balls. In order for a reaction to take place, the molecules must have sufficient kinetic energy. The minimum energy that the molecules of the reacting substances must have in order for the reaction to take place is called the activation energy and is denoted as E a. In a system consisting of a large number of molecules, there is a distribution of molecules by energy, some of them have low energy, some have high and medium energy. Of all these molecules, only a small fraction of the molecules have an energy greater than the activation energy.

As you know from a physics course, temperature is actually a measure of the kinetic energy of the particles that make up a substance. That is, the faster the particles that make up a substance move, the higher its temperature. Thus, obviously, by increasing the temperature we essentially increase the kinetic energy of molecules, as a result of which the proportion of molecules with energy exceeding E a increases and their collision will lead to a chemical reaction.

Fact positive influence Temperature on the rate of reaction was empirically established by the Dutch chemist Van't Hoff back in the 19th century. Based on his research, he formulated a rule that still bears his name, and it goes like this:

The speed of any chemical reaction increases 2-4 times with an increase in temperature by 10 degrees.

The mathematical representation of this rule is written as:

Where V 2 And V 1 is the speed at temperatures t 2 and t 1, respectively, and γ is the temperature coefficient of the reaction, the value of which most often lies in the range from 2 to 4.

Often the speed of many reactions can be increased using catalysts.

Catalysts are substances that speed up the course of a reaction without being consumed.

But how do catalysts increase the rate of a reaction?

Let's remember about the activation energy E a. Molecules with an energy lower than the activation energy in the absence of a catalyst cannot interact with each other. Catalysts change the path along which a reaction proceeds, just as an experienced guide will route an expedition not directly through a mountain, but with the help of detour paths, as a result of which even those companions who did not have enough energy to climb a mountain will be able to move to another her side.

Despite the fact that the catalyst is not consumed during the reaction, it nevertheless takes an active part in it, forming intermediate compounds with the reagents, but by the end of the reaction it returns to its original state.

In addition to the above factors affecting the reaction rate, if there is an interface between the reacting substances (heterogeneous reaction), the reaction rate will also depend on the contact area of the reactants. For example, imagine a granule of aluminum metal that is dropped into a test tube containing an aqueous solution of hydrochloric acid. Aluminum is an active metal that can react with non-oxidizing acids. With hydrochloric acid, the reaction equation is as follows:

2Al + 6HCl → 2AlCl 3 + 3H 2

Aluminum is a solid, which means that the reaction with hydrochloric acid occurs only on its surface. Obviously, if we increase the surface area by first rolling out the aluminum granule into foil, we will thereby provide large quantity aluminum atoms available for reaction with acid. As a result, the reaction rate will increase. Similarly, increasing the surface area of a solid can be achieved by grinding it into powder.

Also, the rate of a heterogeneous reaction in which a solid reacts with a gaseous or liquid substance is often positively influenced by stirring, which is due to the fact that as a result of stirring, the accumulated molecules of reaction products are removed from the reaction zone and a new portion of reactant molecules is “brought in.”

Lastly, it should also be noted the enormous influence on the rate of reaction and the nature of the reagents. For example, the lower an alkali metal is in the periodic table, the faster it reacts with water, fluorine, among all halogens, reacts most quickly with hydrogen gas, etc.

Summarizing all of the above, the speed of the reaction depends on the following factors:

1) concentration of reagents: the higher, the greater the reaction rate

2) temperature: with increasing temperature, the rate of any reaction increases

3) contact area of reacting substances: than larger area contact of reagents, the higher the reaction rate

4) stirring, if a reaction occurs between a solid and a liquid or gas, stirring can speed it up.

Chemical reaction rate

Chemical reaction rate- change in the amount of one of the reacting substances per unit of time in a unit of reaction space. Is a key concept in chemical kinetics. The rate of a chemical reaction is always a positive value, therefore, if it is determined by the starting substance (the concentration of which decreases during the reaction), then the resulting value is multiplied by −1.

For example for the reaction:

the expression for speed will look like this:

. The rate of a chemical reaction at any given time is proportional to the concentrations of the reactants raised to powers equal to their stoichiometric coefficients.

For elementary reactions, the exponent of the concentration of each substance is often equal to its stoichiometric coefficient; for complex reactions this rule is not observed. In addition to concentration, the following factors influence the rate of a chemical reaction:

the nature of the reactants,
the presence of a catalyst,
temperature (van't Hoff rule),
pressure,
surface area of reacting substances.

If we consider the simplest chemical reaction A + B → C, we will notice that instant The speed of a chemical reaction is not constant.

Literature

Kubasov A. A. Chemical kinetics and catalysis.
Prigogine I., Defey R. Chemical thermodynamics. Novosibirsk: Nauka, 1966. 510 p.
Yablonsky G.S., Bykov V.I., Gorban A.N., Kinetic models of catalytic reactions, Novosibirsk: Nauka (Sib. Department), 1983. - 255 p.

Wikimedia Foundation. 2010.

See what “Rate of a chemical reaction” is in other dictionaries:

Basic concept of chemical kinetics. For simple homogeneous reactions, the rate of a chemical reaction is measured by the change in the number of moles of the reacted substance (at a constant volume of the system) or by the change in the concentration of any of the starting substances... Big Encyclopedic Dictionary

RATE OF CHEMICAL REACTION- the basic concept of chemistry. kinetics, expressing the ratio of the amount of reacted substance (in moles) to the period of time during which the interaction occurred. Since the concentrations of reactants change during interaction, the rate is usually ... Big Polytechnic Encyclopedia

rate of chemical reaction- a quantity characterizing the intensity of a chemical reaction. The rate of formation of a reaction product is the amount of this product as a result of a reaction per unit time per unit volume (if the reaction is homogeneous) or per... ...

A quantity characterizing the intensity of a chemical reaction (See Chemical reactions). The rate of formation of a reaction product is the amount of this product resulting from a reaction per unit time per unit volume (if... ...

Basic concept of chemistry kinetics. For simple homogeneous reactions of S. x. R. measured by the change in the number of moles of reacted in va (with a constant volume of the system) or by the change in the concentration of any of the initial in va or reaction products (if the volume of the system ...

For complex reactions consisting of several stages (simple or elementary reactions), a mechanism is a set of stages, as a result of which the starting materials are converted into products. Molecules can act as intermediates in these reactions... ... Natural science. encyclopedic Dictionary

- (eng. nucleophilic substitution reaction) substitution reactions in which the attack is carried out by a nucleophilic reagent carrying a lone electron pair. The leaving group in nucleophilic substitution reactions is called a nucleofuge. Everything... Wikipedia

Transformation of some substances into others, different from the original ones chemical composition or building. Total number of atoms of each of this element, as well as themselves chemical elements, the constituent substances, remain in R. x. unchanged; this R. x... Great Soviet Encyclopedia

drawing speed- linear speed of metal movement at the exit from the die, m/s. On modern drawing machines, the drawing speed reaches 50–80 m/s. However, even when drawing wire, the speed, as a rule, does not exceed 30–40 m/s. At… … Encyclopedic Dictionary of Metallurgy

Physical chemistry: lecture notes Berezovchuk A V

2. Factors affecting the rate of a chemical reaction

For homogeneous, heterogeneous reactions:

1) concentration of reacting substances;

2) temperature;

3) catalyst;

4) inhibitor.

Only for heterogeneous:

1) the rate of supply of reacting substances to the phase interface;

2) surface area.

The main factor is the nature of the reactants - the nature of the bonds between atoms in the molecules of the reactants.

NO 2 – nitrogen oxide (IV) – fox tail, CO – carbon monoxide, carbon monoxide.

If they are oxidized with oxygen, then in the first case the reaction will occur instantly, as soon as you open the cap of the vessel, in the second case the reaction is extended over time.

The concentration of reactants will be discussed below.

Blue opalescence indicates the moment of sulfur precipitation; the higher the concentration, the higher the speed.

Rice. 10

The higher the concentration of Na 2 S 2 O 3, the less time the reaction takes. The graph (Fig. 10) shows a directly proportional relationship. The quantitative dependence of the reaction rate on the concentration of the reacting substances is expressed by the LMA (law of mass action), which states: the rate of a chemical reaction is directly proportional to the product of the concentrations of the reacting substances.

So, basic law of kinetics is an empirically established law: the rate of a reaction is proportional to the concentration of the reactants, example: (i.e. for a reaction)

For this reaction H 2 + J 2 = 2HJ – the rate can be expressed in terms of a change in the concentration of any of the substances. If the reaction proceeds from left to right, then the concentration of H 2 and J 2 will decrease, and the concentration of HJ will increase as the reaction progresses. For the instantaneous reaction rate, we can write the expression:

square brackets indicate concentration.

Physical meaning k– molecules are in continuous motion, collide, fly apart, and hit the walls of the vessel. In order for the chemical reaction to form HJ to occur, the H2 and J2 molecules must collide. The number of such collisions will be greater, the more molecules of H 2 and J 2 are contained in the volume, i.e., the greater the values [H 2 ] and . But molecules move with at different speeds, and the total kinetic energy of the two colliding molecules will be different. If the fastest molecules H 2 and J 2 collide, their energy can be so high that the molecules break into atoms of iodine and hydrogen, which fly apart and then interact with other molecules H 2 + J 2 ? 2H+2J, then H + J 2 ? HJ + J. If the energy of the colliding molecules is less, but high enough to weaken the H – H and J – J bonds, the formation reaction of hydrogen iodide will occur:

For most colliding molecules, the energy is less than that required to weaken the bonds in H 2 and J 2. Such molecules will “quietly” collide and also “quietly” disperse, remaining what they were, H 2 and J 2. Thus, not all, but only part of the collisions lead to a chemical reaction. The proportionality coefficient (k) shows the number of effective collisions leading to a collision reaction at concentrations [H 2 ] = 1 mol. Magnitude k–const speed. How can speed be constant? Yes, uniform speed rectilinear movement called a constant vector quantity, equal to the ratio of the movement of the body over any period of time to the value of this interval. But molecules move chaotically, then how can the speed be const? But a constant speed can only be at a constant temperature. With increasing temperature, the proportion of fast molecules whose collisions lead to a reaction increases, i.e., the rate constant increases. But the increase in the rate constant is not unlimited. At a certain temperature, the energy of the molecules will become so great that almost all collisions of the reactants will be effective. When two fast molecules collide, a reverse reaction will occur.

There will come a moment when the rates of formation of 2HJ from H 2 and J 2 and decomposition will be equal, but this is already chemical equilibrium. The dependence of the reaction rate on the concentration of the reactants can be traced using the traditional reaction of interaction of a solution of sodium thiosulfate with a solution of sulfuric acid.

Na 2 S 2 O 3 + H 2 SO 4 = Na 2 SO 4 + H 2 S 2 O 3, (1)

H 2 S 2 O 3 = S? + H 2 O + SO 2?. (2)

Reaction (1) occurs almost instantly. The rate of reaction (2) depends at a constant temperature on the concentration of the reactant H 2 S 2 O 3. This is exactly the reaction we observed - in this case, the speed is measured by the time from the beginning of the solutions to merge until the appearance of opalescence. In the article L. M. Kuznetsova The reaction of sodium thiosulfate with hydrochloric acid is described. She writes that when solutions are drained, opalescence (turbidity) occurs. But this statement by L.M. Kuznetsova is erroneous since opalescence and turbidity are two different things. Opalescence (from opal and Latin escentia– suffix meaning weak effect) – scattering of light by turbid media due to their optical inhomogeneity. Light scattering– deviation of light rays propagating in a medium in all directions from the original direction. Colloidal particles are capable of scattering light (Tyndall-Faraday effect) - this explains opalescence, a slight turbidity of the colloidal solution. When carrying out this experiment, it is necessary to take into account the blue opalescence, and then the coagulation of the colloidal suspension of sulfur. The same density of the suspension is noted by the visible disappearance of any pattern (for example, a grid on the bottom of a cup) observed from above through the layer of solution. Time is counted using a stopwatch from the moment of draining.

Solutions of Na 2 S 2 O 3 x 5H 2 O and H 2 SO 4.

The first is prepared by dissolving 7.5 g of salt in 100 ml of H 2 O, which corresponds to a 0.3 M concentration. To prepare a solution of H 2 SO 4 of the same concentration, you need to measure 1.8 ml of H 2 SO 4 (k), ? = = 1.84 g/cm 3 and dissolve it in 120 ml of H 2 O. Pour the prepared Na 2 S 2 O 3 solution into three glasses: 60 ml in the first, 30 ml in the second, 10 ml in the third. Add 30 ml of distilled H 2 O to the second glass, and 50 ml to the third glass. Thus, in all three glasses there will be 60 ml of liquid, but in the first the salt concentration is conditionally = 1, in the second – ½, and in the third – 1/6. After the solutions have been prepared, pour 60 ml of H 2 SO 4 solution into the first glass with a salt solution and turn on the stopwatch, etc. Considering that the reaction rate decreases with dilution of the Na 2 S 2 O 3 solution, it can be determined as a quantity inversely proportional to time v = 1/? and construct a graph, plotting the concentration on the abscissa axis, and the reaction rate on the ordinate axis. The conclusion from this is that the reaction rate depends on the concentration of substances. The data obtained are listed in Table 3. This experiment can be performed using burettes, but this requires a lot of practice from the performer, because the graph may be incorrect.

Table 3

Speed and reaction time

The Guldberg-Waage law is confirmed - professor of chemistry Gulderg and young scientist Waage).

Let's consider the next factor - temperature.

As temperature increases, the speed of most chemical reactions rises. This dependence is described by Van't Hoff's rule: “For every 10 °C increase in temperature, the rate of chemical reactions increases by 2 to 4 times.”

Where ? – temperature coefficient showing how many times the reaction rate increases when the temperature increases by 10 °C;

v 1 – reaction rate at temperature t 1 ;

v 2 – reaction rate at temperature t2.

For example, a reaction at 50 °C takes two minutes, how long will it take for the process to complete at 70 °C if the temperature coefficient ? = 2?

t 1 = 120 s = 2 min; t 1 = 50 °C; t 2 = 70 °C.

Even a slight increase in temperature causes a sharp increase in the reaction rate of active collisions of the molecule. According to activation theory, only those molecules whose energy is greater than the average energy of molecules by a certain amount participate in the process. This excess energy is activation energy. Its physical meaning is the energy that is necessary for the active collision of molecules (rearrangement of orbitals). The number of active particles, and therefore the reaction rate, increases with temperature according to an exponential law, according to the Arrhenius equation, which reflects the dependence of the rate constant on temperature

Where A - Arrhenius proportionality coefficient;

k– Boltzmann's constant;

E A – activation energy;

R – gas constant;

T- temperature.

A catalyst is a substance that accelerates the rate of a reaction without being consumed.

Catalysis– the phenomenon of changing the reaction rate in the presence of a catalyst. There are homogeneous and heterogeneous catalysis. Homogeneous– if the reagents and the catalyst are in the same state of aggregation. Heterogeneous– if the reagents and catalyst are in different states of aggregation. About catalysis, see separately (further).

Inhibitor– a substance that slows down the rate of reaction.

The next factor is surface area. The larger the surface area of the reactant, the greater the speed. Let us consider, using an example, the effect of the degree of dispersion on the reaction rate.

CaCO 3 – marble. Dip the tiled marble into hydrochloric acid HCl, wait five minutes, it will dissolve completely.

Powdered marble - we will do the same procedure with it, it will dissolve in thirty seconds.

The equation for both processes is the same.

CaCO 3 (solid) + HCl (g) = CaCl 2 (solid) + H 2 O (liquid) + CO 2 (g) ?.

So, when adding powdered marble, the time is less than when adding slab marble, for the same mass.

With an increase in the interface surface, the rate of heterogeneous reactions increases.

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Chemical reaction rate

For example for the reaction:

the expression for speed will look like this:

. The rate of a chemical reaction at any given time is proportional to the concentrations of the reactants raised to powers equal to their stoichiometric coefficients.

the nature of the reactants,
the presence of a catalyst,
temperature (van't Hoff rule),
pressure,
surface area of reacting substances.

If we consider the simplest chemical reaction A + B → C, we will notice that instant The speed of a chemical reaction is not constant.

Literature

Kubasov A. A. Chemical kinetics and catalysis.
Prigogine I., Defey R. Chemical thermodynamics. Novosibirsk: Nauka, 1966. 510 p.
Yablonsky G.S., Bykov V.I., Gorban A.N., Kinetic models of catalytic reactions, Novosibirsk: Nauka (Sib. Department), 1983. - 255 p.

Wikimedia Foundation. 2010.

Welsh dialects of English
Saw (film series)

See what “Rate of a chemical reaction” is in other dictionaries:

RATE OF CHEMICAL REACTION- the basic concept of chemical kinetics. For simple homogeneous reactions, the rate of a chemical reaction is measured by the change in the number of moles of the reacted substance (at a constant volume of the system) or by the change in the concentration of any of the starting substances... Big Encyclopedic Dictionary

rate of chemical reaction- the basic concept of chemical kinetics. For simple homogeneous reactions, the rate of a chemical reaction is measured by the change in the number of moles of the reacted substance (at a constant volume of the system) or by the change in the concentration of any of the starting substances... encyclopedic Dictionary

Chemical reaction rate- a quantity characterizing the intensity of a chemical reaction (See Chemical reactions). The rate of formation of a reaction product is the amount of this product resulting from a reaction per unit time per unit volume (if... ...

RATE OF CHEMICAL REACTION- basic concept of chemistry kinetics. For simple homogeneous reactions of S. x. R. measured by the change in the number of moles of reacted in va (with a constant volume of the system) or by the change in the concentration of any of the initial in va or reaction products (if the volume of the system ...

MECHANISM OF CHEMICAL REACTION- For complex reactions consisting of several. stages (simple or elementary reactions), a mechanism is a set of stages, as a result of which the starting materials are converted into products. Molecules can act as intermediates in these reactions... ... Natural science. encyclopedic Dictionary

Nucleophilic substitution reactions- (eng. nucleophilic substitution reaction) substitution reactions in which the attack is carried out by a nucleophilic reagent carrying a lone electron pair. The leaving group in nucleophilic substitution reactions is called a nucleofuge. Everything... Wikipedia

Chemical reactions- transformation of some substances into others, different from the original ones in chemical composition or structure. The total number of atoms of each given element, as well as the chemical elements themselves that make up the substances, remain in R. x. unchanged; this R. x... Great Soviet Encyclopedia