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STUDENTS' DÎFFÎCULTÎES iN THE FiELD OF CHEMiCAL KlNETiCS iN SECONDARY _SCHOOLS AND METHODOLOGICAL PRINCIPLES OF THEÏR ELÎMÎNATÎON._
DOI: 10.31618/ESU.2413-9335.2020.L8L1190 Nuriyeva Matanat Sarkhan
Dissertation candidate under the program of Doctor of Philosophy Azerbaijan State Pedagogical University
ABSTRACT
In the article the main purpose is the development of new teaching methods that meet the learning difficulties in the field of chemical kinetics, which has been considered the most pressing problem in the teaching process of chemistry in secondary schools during recent years. Thus, in the article, in the direction of overcoming these difficulties in secondary schools, research-based criteria have been highlighted for selecting new pedagogical experiments by researching new methodological principles intended to be used in the teaching prosess of topics related to chemical kinetics with the application of modern training technologies and also the scheme reflecting the modeling methodology of the teaching process of chemical kinetics.
Keywords: chemical kinetics, rate of chemical reaction, collision theory, homogeneous reactions, catalyst
INTRODUCTION: A number of problems arising in the organization and teaching of topics related to chemical kinetics in the teaching process of chemistry create certain difficulties in the direction of grasping of the subject by students more accurately. According to our research, we should note that in secondary schools with the application of modern learning technologies the teaching process of the topic related to chemical kinetics should be based on the following methodological principles:
• Classification of chemical reactions to determine the role of chemical kinetics in the process of chemical reactions course;
• The role of determining the rate of chemical reactions in the teaching of chemistry during carrying out chemical reactions;
• The role of example solving in mastering theoretical knowledge of chemistry in the process of studying the rate of chemical reactions and the factors affecting the rate of chemical reactions;
• The using possibilities of chemical kinetics on the basis of modern learning technologies in the teaching process of chemistry.
The creation of real-cognitive motivation and i.e the desire of acquiring knowledge, based on the active learning principles in students in the organization and teaching prosess of chemistry lessons is one of the main issue. We should note that although giving students mathematical knowledge in this area has a positive effect on students' understanding of the main ideas, but based on our research, we can say that most of the difficulties they face are conceptual in nature.
According to our research, we can say that, our main goal in developing the scheme of teaching methodology of "The process of studying the rate of chemical reactions and factors affecting the rate of
chemical reactions" is correctly explaining the concepts and laws of the theme in the teaching process of the theme of chemical kinetics, and creating a conducive learning environment for students based on their explanations, to deepen their knowledge based on solving computational examples independently. Thus, the concepts system related to the topic should be defined on the basis of the principles that play an exceptional role in the formation of real-cognitive motivation in students in the process of teaching lessons: [1.p.39-40]
> Knowledge should be acquired and mastered independently, productively and creatively;
> Logical, critical and creative thinking, as well as solving problems and skills for decision-making should be formed;
> Scientific-research habits should be formed
Based on our theoretical and practical research, we
can say that if a student discovers new knowledge on the subject, both conceptually and mathematically within his own activities, it means that he (she) approaches the lesson more independently and creatively.
Thus, we present a scheme reflecting the methodology of teaching of chemical kinetics in secondary schools. Our main goal in compiling this scheme is to ensure the dynamic development of the taught topics in the direction of both theoretical, practical and independent example solving. We plan to determine the direction in which this methodological scheme that we are researching on will result based on the experiments we will put in schools.
Scheme 1.
Scheme reflecting the methodology of modeling of the teaching process of chemical kinetics:
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The rate of chemical reactions and the factors affecting the rate of chemical reactions - Substances react with each other in that case, when it breaks or weakens into chemical bonds between the atoms in its molecule. To break or weaken these bonds, molecules must have a certain amount of energy. The amount of energy that molecules have for entering a chemical reaction is called the activation energy [2.p.52].
The rate of a chemical reaction is the change of density of one of the substances entering the reaction and obtaining at a single time. For example, for the reaction Aa<q) +bB(q)^Dd(q)
e = -A£a; d = -è£B . =
At At At
if we summarize these, then:
It will be d,,m = + — , as C= -, then it is
um ~ At V
Av
^ = +T" AT
Various factors affect to the rate of a chemical reaction. First of all, before conducting chemical reactions, every chemistry teacher should teach students the importance of the specification of the conditions under which they are carried out, the rate of reactions and carrying out time, and a correct and systematic understanding of the methods of solving examples related to the rate of reactions, using the necessary visual aids.
Factors affecting the rate of a chemical reaction:
1. The effect of the chemical nature of substances to the reaction rate - While saying the
chemical nature of a substance, its structure, composition, and the type of communication between the particles is understood. As different substances conditioned by the mentioned parameters have different natures, the rates of their interactions with the same substance also differ from each other [3..p.129]. For example, in the electrochemical stress range of
metals, metals up to magnesium normally react with water, metals between magnesium and hydrogen react with water when heated, post-hydrogen metals do not react with water, even when heated. We conclude from this that, the more active the metal will be the reaction goes so fast.
2. Effect of density to reaction rate - The effect of density to the reaction rate is mainly related to reactions in gaseous media and solutions. Here the teacher must explain to the students the essence of the concepts of rate law of the reaction or the kinetics of reaction.
While saying rate law of a reaction, it is intended an equation that determines the subordination between the density of the substances entering the reaction with any time related to the course of the reaction. Exactly this equation shows the subordination of the rate of the reaction from the density of the initial substances.
For the reaction
Aa(q) +bB(q)^Dd(q) 6 = k
ra
rb
Here k - is the rate constant for a given reaction, it depends on the nature and temperature of the substances entering the reaction. It does not depend on other factors. In homogeneous reactions, the rate of the reaction is directly proportional to the multiplication of the density of the reagents, ie the initial substances [4]. As the density of the substances increases, the rate of the reaction increases, and as the density decreases, it decreases. Thus, a change of the pressure of gas or the density causes a change of the number of particles in a certain volume and, accordingly a change of the number of collisions of particles in a single volume. As the number of collisions changes, so will the rate of the reaction.
Due to the change of the fluidity, the rate of the reaction Aa (q) + bB (q) ^ Dd (q) C2-C1 is calculated by the formula tf = +— = tf = ;
AT AT ^•AT
As well as X2 -d = k^Cf
rb
Example 1. What equation does the rate formula
t9 = k • CX2 • Cy2 belong to?
t t
A)X2(q) +Y2(q) ^ 2XY(q) C) X2(q) +Y2(q) ^ X2Y2(q)
t t
B) X2(q) +2Y2(q) ^ 2XY2(q) D) X2(q) +3Y2(q) ^
2XY3(q)
Solution: It is also clear to the students from the speed formula that the coeffisient of X2 must be 1 because there is no elevation in its density expression, and as in the density expression of Y2 there is elevation 3, therefore the coeffisient must be 3. Then the answer D is correct.
But in heterogeneous reactions, the change of the surface radius of the substances being interacting reaction causes an increase the number of collisions of liquids or gases with the surface of the hard substance. Again, a change of the number of collisions causes a change of the rate of chemical reactions, and the rate of such reactions is calculated by the formula ti = —. It
J S-AT
is explained to students in a simpler way:
In heterogeneous reactions, the rate of the reaction turns directly proportional upon the radius of the surface of the hard substance (from the crushing of the hard substance into a powder condition) and the pressure of the gaseous substance. Example;
I. 4Al(b) + 3O2M ^ 2Al2Os(b) ti = k • SAl • P^
Pn
>»2(q) l9 = k • Sc • P02
II. S(b)+O2(q) ^ SO2(q) ti = k^Ss
III. C(b) + O2(q) ^ CO2 In these formulas that we mentioned, the rate of
the reactions of combustion of Al, S and C depends on
the density of the gas phase and the area of surface of the hard phase. S- indicates the area of surface of the hard substance. Over a period of time as the area of surface of the hard substance (S) does not change, in the above formulas the multiplication of k • S remains constant . Thus, this multiplication is marked by a constant quantity k and is written as follows:
I. ti = ks^ Pq2 II. ti = ks^ PQ2 III. ti = ks^ PQ2
In these formulas, Ks - is the coefficient of proportionality, which takes into account the rate constant of the reaction and the area of the contact surface.
Example 2.
What experiments if we conduct in the 3Fe + 2O2^ Fe3O4 reaction, the rate of the reaction will increase?
1) To crush Fe into a powder condition
2) To increase the pressure of oxygen
3)To reduce the density of oxygen
Solution: Thus, to increase the speed of this reaction;
I.To increase the contact surface of Fe, it is necessary to pulverize it.
II. To increase the pressure or to increase the density of oxygen
So, the correct option is I and II.
In this case, the teacher must explain more deeple to the students the essence of the "Collision Theory", which is the basis of the "theory of the kinetics of chemical reactions" in order to instill in students the essence of the topic more deeple. Thus, it is advisable to use the following scheme:
The effect of temperature on the reaction rateA change of temperature causes a change of the kinetic energy of the particles, this means that the particles have a certain energy to break the existing bonds. The energy that a particles have in order for them to react is called the activation energy.
What does the rising of the temperature of the system cause?
1.To increasing of the level of kinetic energy;
2. To increasing of the price of average kinetic energy;
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3. It creates condition for increasing of the number of particles that have higher energy than the activation energy.
The effect of the catalyst on the reaction rate-
The catalyst entering into the system reduces the required activation energy, as a result, interaction resulting with formation of many products of the particles occur. Substances that change the rate of the reaction but remain chemically unchanged at the end of the process are called catalysts. To explain the role of the catalyst more clearly to students, we present the following example:
In order to observe the catalytic role of water, which we all know well, we mix crushed solid iodine crystals with zinc powder. So no change occurs, no reaction go. But when 2-3 drops of water are added to the mixture, we will observe that some of the unreacted iodine turns into a purple vapor as a result of the heat release, and the reaction proceeds. So, Zn and J2, which do not react under normal conditions, react violently under the influence of the catalyst:
H20
Zn + J2—> ZnJ2
It should be noted that the catalyst ensures the reaction to proceed in such a way, the activation energy to be minimal:
1)Increasing of the number of particles resulting with the formation of a product directed in the desired direction;
2)The density of substances entering reaction on the surface of the catalyst increases;
3) The change of the occuring nature of the reaction goes through the very energy consumption of a series of simple transformations instead of one stage;
4) The establishment of more active centers that can be restored after the end of the reaction;
5) Increasing of reactivity of active centers.
It should be noted that although there is currently
no general theory of the catalysis process, the selection
and application of catalysts is determined empirical
way. The effect of catalysts is due to their active
participation in the reaction in the formation of active
intermediate compounds. We present a scheme
showing the participation mechanism of the catalyst:
k
The stages of A + B ^ AB reaction (general reaction) (k is catalyst):
1. A+k ^ Ak
2. Ak + B ^ AB+k
Let's look at the effect mechanism of the catalyst in the example of contact oxidation of SO2 to SO3 in the presence of catalyst V2O5: [5..p., 80-81.]
V2O5
SO2 + O2-> SO3 (general reaction)
V2O5 + SO2^ V2O4 + SO3 V2O4 + SO2 + O2 ^ 2VOSO4
Thus, the intermediate compound VOSO4, decomposes under the influence of temperature.
2VOSO4^ V2O5 + SO3 + SO2
As can be seen, V2O5 increases the rate of the reaction by forming an intermediate substance, but remains the same at the end of the reaction.
Result:In the article, in the teaching process of the rate of chemical reactions and the factors that affect it, by the teacher based on the principle of active collaboration of learning, important processes have been studied in the direction of correctly explaining concepts and laws related to the topic, of deepening students' knowledge based on their solving computational examples independently on the basing of their explanations and of building the skills to apply this knowledge in their future lives.
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