Factors Influencing the Rate of Reactions

Eveiy chemical reaction requires some time for its complctiQn, but some reactions arc very fast and some arc very slow. Reactions between ions in solution without changc in oxidation state arc usually extremely fast. An example is the neutralization of an acid by a base, which proceeds as fast as the solutions can be mixed. Presumably nearly every time a hydronium ion collides with a hydroxide ion reaction occurs, and the number of collisions is vciy great, so that there is little delay in the reaction. The formulation of a precipitate, such as that of silver chloridc when a solution containing silver ion is mixed with a solution containing chloride ion, may require a few seconds, to permit the ions to diffuse together to form the crystalline grains of the precipitate:

Ag*(aq) + Cl-(aq) AgCl(c).

On the other hand, ionic oxidation-reduction reactions arc sometimes very slow. An example is the oxidation of a stannous ion by a ferric ion:

гРс^ + Зп^гРс^ + Бп⁴'.

This reaction does not occur every time a stannous ion collides with one or two ferric ions. In order for a reaction to take placc, the collision must be of such a nature that electrons can be transferred from one ion to another, and collisions that permit this electron transfer to occur may be rare.

An example of a reaction that is extremely slow at room temperature is that between hydrogen and oxygen:

2H₂ + 0₂->2H₂0.

A mixture of hydrogen and oxygen can be kept for years but we can observe no appreciable reaction taking placc.

That is why it is not unusual to hear chemists speaking about the factors that determine the rate of a reaction. These arc manifold. The rate depends not only upon the composition of the reacting substances, but also upon their physical form, the intimacy of their mixture, the temperature and pressure, the concentrations of the rcactants, special physical circumstances such as irradiation with visible light, ultraviolet light, X-rays, neutrons, or other waves or particlcs, and the presence of other substances that affect the reaction but are not changcd by it.

Words and Word-Combinations to Be Memorized

affect, appreciable, collide, collision, concentration, ferric, a few, on the other hand, influence, ion, ionic, neutralization, in order for, permit, proceed, reduction, take place, that is why, transfer, ultraviolet, unusual, visible, wave, X-ray

Ex. 5. Give the Russian equivalents for the following:

require time for, oxidation state, be extremely fast, nearly cvciy time, collide with, form the precipitate, oxidation-rcduction reactions, in order for a reaction to take place, transfer electrons, observe a reaction, the intimacy of mixture, irradiation with light, ultraviolet light, affect the reaction, hydronium ion

Ex. 6. Give the English equivalents for the following:

влиять на скорость реакции, без изменения окислительного со­стояния, нейтрализация кислоты основанием, смешивать растворы, число столкновений, так что, такой как, хлорид ссребра, несколько секунд, с другой стороны, сталкиваться для того чтобы, при комнат­ной температуре, смесь водорода и кислорода, наблюдать, вот поче­му, зависеть от, видимый свет, рентгеновские лучи

Ex. 7. Fill in the blanks with prepositions where necessary.

1. One can give ... an example ... a reaction which may require ... a few scconds ... its completion. 2.... the other hand, oxidation-reduction reactions are sometimes very slow. 3. An example ... a reaction that is extremely slow... room temperature is that... hydrogen and oxygen. 4. It is quite usual to hear chemists speaking ... the factors that influcncc ... the rate ... a reaction. 5. The reaction rate depends ... many factors.

6. Sometimes the presence ... other substanccs affects ... the reaction.

7. Every reaction takes different time ... its completion.

Ex. 8. Translate the sentences into Russian, paying attention to different functions of the word order.

1. St. Petersburg University was awarded the Order of Lenin in 1944 and the Order of the Red Banner of Labour in 1969.2. In arranging his ideas for the book Principles of Chemistry Mcndclcycv felt the need to bring to inorganic chcmistry the same degree of order that was being achieved in organic chcmistry. 3. Wc were ordered to start the work immediately. 4. In order for a reaction to take placc, the collision between the ions must result in the transfer of electrons from one ion to another. 5. In order that the reaction might occur, the reactants should be heated. 6. Wc must measure all the parameters in order to summarize them in a table. 7. Crystalline compounds have their atoms arranged in a certain order.

Ex. 9. Translate the sentences into Russian.

1. The door was open and wc could hear Prof. N giving his lecture.

2. Coming up to him for the second time I found his experiment finished.

3. Wc saw the powder darkening when it was exposed to light. 4. We shall have our papers checkcd and then wc shall be permitted to do the experimental part. 5. Wc all heard her saying so.Ss ^wc may treat the

 

clcctrons in the shared electron pair as belonging to both atoms. 7. We usually think of a substancc as being in a certain physical state. 8. Solutions arc often thought of as being liquids. 9. They watchcd the sugar ciystals disappearing in water. 10. Lavoisier considered oxygen as being a constituent of all acids. 11. After Dalton wc find the atomic theory developed rather than rejected. 12. The inertness of the noble gases is accountcd for by the fact that they have all their shells completely filled. 13. Wc had our laboratory equipped by the beginning of a new acadcmic year. 14. Wc saw the solution turning blue as the reaction proceeded. 15. They observed the temperature slowly rising.

Ex. 10. Translate the sentences into English.

1. Все химические реакции происходят с различной скоростью.

2. Скорость реакции зависит от состава реагирующих веществ и ус­ловий реакции. 3. Существует множество факторов, которые оказы­вают влияние на реакцию. 4. Среди них прежде вссго следует на­звать температуру, концентрацию, наличие катализаторов и другие. 5. С точки зрения молекулярной кинетики легко объяснить влияние температуры. 6. Иногда скорость реакции в значительной степени зависит от присутствия катализатора.

Ex. 11. Answer the following questions:

1. What reactions procccd fast? 2. What reactions arc usually slow?

3. In what way is silver chloridc formed? 4. What example of oxidation- reduction reaction can you give? 5. What factors influence the reaction rate? 6. In what way can one classify these factors?

Section II

Упр. 1. Назовите значения следующих интернациональных слов:

catalyst, speed, specific, action, laboratoiy, industry, biological, system, manufacture, margarine, regulate, enzyme, majority, practically, phenomenon, material, catalysis, elementary, regenerate

Упр. 2. Определите значения выделенных слов по контексту.

1. Among the factors that alter the rate of a chemical reaction arc temperature, concentration, etc. 2. Sometimes, when the work is especially difficult, wc ask for aid. 3. A particular property of a catalyst is that it is not consumed in the reaction. 4. When a compound has some quantity of a foreign substancc, it cannot be considered pure.

Слова к тексту:

digestion — переваривание (лш</м); augment — увеличивать; provide— обеспечивать

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