 |
Asia-Pacific Forum
on Science Learning and Teaching, Volume 11, Issue 2, Article 2 (Dec., 2010) |
The results showed that there was no statistically significant difference between the groups with respect to their prior knowledge level (p > .05). These results indicated that students in both experimental and control groups were similar regarding the pretest (CEMT) scores (see Table IX).
Table IX. ANOVA Results of Pre-Test
School
Groups
N
X
F
p
Pre- Test
A
Control
27
35.7037
.097
.756
Experimental
26
35.0769
B
Control
20
28.8000
.002
.964
Experimental
18
28.8889
C
Control
30
39.7333
.185
.669
Experimental
30
40.4000
The results of the post-test reflected that mean scores of experimental groups were higher than control groups and there were significant differences (p <.05). This result showed that teaching with analogies caused a significantly better acquisition of the concept than the traditional instruction (see Table X). The main difference between the two methods was that the analogies oriented instruction explicitly dealt with students’ misconceptions relating chemical equilibrium while the traditional method did not.
Table X. ANOVA Results of Post-Test
School
Groups
N
X
F
p
Post-Test
A
Control
27
47.8519
27.611
.000
Experimental
26
57.2308
B
Control
20
42.6000
12.336
.001
Experimental
18
50.4444
C
Control
30
51.2000
44.272
.000
Experimental
30
65.0667
Also, the t-test was used to determine if there was any significant difference between pre-test and post-test scores in the experimental and control groups. The level of significance was set at p= .05. When the results of the experimental groups’ pre and post-test scores were analyzed using t-test, it was determined that there was a statistically significant difference between pre and post-test scores. For example, the experimental group in A high school went from a mean score of 35.07 to 57.23 (t =-12.458 and p= 0.00, p < .05), the experimental group in B high school went from a mean score of 28.88 to 50.44 (t = -13.038 and p = 0.00, p < .05) and the experimental group in C high school went from a mean score of 40.40 to 65.06 ( t = -13.053 and p = 0.00, p < .05). Similarly, there was a significant improvement of the mean scores from the pre-test to post-test in the control groups. The control group in A high school went from a mean score of 35.70 to 47.85 (t = -9.055 and p= 0.00, p <.05), the control group in B high school went from a mean score of 28.80 to 42.60 (t= -9.564 and p = 0.00, p <.05) and the control group in C high school went from a mean score of 39.73 to 57.23( t = -9.899 and p= 0.00, p <.05).
Semi- Structed Interviews
Questions in the interview and analysis are presented below.
Question 1. Consider the following equilibrium system;
CO (g) + Cl2 (g)
CO Cl2 (g) + heat
What do you understand from the statement that, “the system reaches equilibrium?” Table XI gives response categories and their frequencies and percentages relating to this question.
Table XI. The Categories Belonging to First Interview Question
Student’s View
A High School
B High School
C High School
Experimental
Control
Experimental
Control
Experimental
Control
The rates of the forward and reverse reactions are equal when the system reaches equilibrium. *
7
58.3
3
25.0
4
33.3
1
8.3
5
41.7
2
16.7
Reaction continues even though it seems to have ceased.*
3
25.0
0
0.0
2
16.7
0
0.0
6
50.0
2
16.7
Display with two arrows.*
0
0.0
0
0.0
0
0.0
0
0.0
2
16.7
0
0.0
Existence of all the reactants and the products in the reaction.*
0
0.0
0
0.0
0
0.0
0
0.0
2
16.7
0
0.0
Concentration of the reactants must equal the concentration of the products at equilibrium
0
0.0
3
25.0
2
16.7
2
16.7
0
0.0
0
0.0
Mass of all species in the reaction mixture is equal at equilibrium.
0
0.0
0
0.0
0
0.0
0
0.0
1
8.3
3
25.0
Balancing chemical equation.
0
0.0
0
0.0
1
8.3
3
25.0
0
0.0
0
0.0
No changes in the chemical reaction.
0
0.0
0
0.0
1
8.3
1
8.3
0
0.0
0
0.0
Completion of the reaction.
0
0.0
0
0.0
0
0.0
0
0.0
0
0.0
2
16.7
Procedures about the molarity.
0
0.0
1
8.3
0
0.0
0
0.0
0
0.0
0
0.0
Equivalence of the moles via molarity.
0
0.0
1
8.3
0
0.0
0
0.0
0
0.0
0
0.0
Trying to change the reaction into its previous condition.
0
0.0
1
8.3
0
0.0
0
0.0
0
0.0
0
0.0
Forward and reverse activation energies are equal at equilibrium.
0
0.0
1
8.3
0
0.0
0
0.0
0
0.0
0
0.0
Stabilization of the temperature’s heat.
0
0.0
0
0.0
0
0.0
1
8.3
0
0.0
0
0.0
* correct explanations
It is understood from Table XI that the number of students in the experimental groups who can explain the equilibrium correctly as “rate of the forward and reverse reaction are equal at equilibrium” or “reaction continues even though it seems to have ceased” is higher than the control groups. Morever, although experimental groups have some misconceptions such as “equilibrium is the equivalence of the concentration of reactive and products or the equivalence of the masses and balancing chemical equation”, control groups have more misconceptions comparing to the experimental groups. This results showed that experimantal groups have better acquisition of chemical equilibrium concept than the control groups. Some of the explanations of students in the experimental groups are below:
“Features like pressure, colour and concentration do not change if the system reaches equilibrium. However, the act among molecules continues. There is a convertion from reactants to products and from products to reactants. The reaction seems to have ceased but the move goes on.” SC6
“If the rates of the reverse and forward reaction are equal, then the reaction reaches equilibrium. It seems as if there is no change but reaction continues.”SB7
“When the rate of forward reaction and reverse reaction are equal, system will reach equilibrium.” SA1
When explanations of students in control groups are analysed, it is seen that most of the students explain concept of equilibrium correctly consisted of the most successful students according to their pos-test scores. Namely, while percentage of true explanations intensified among the students with higher conginitive development students, this percentage was very low among students with medium and lower cognitive development. According to the students’ expressions, it was determined that the concept of equilibrium was associated with everyday terms such as equality and balance or perceptions as completion of the reaction because of macroscobic events stopped. The following views can be given as an example to these views:
“When the system reached equilibrium, the reaction completed. The amount of the reactants and the products is the same.”SA13
“Concentration of the reactants and products are equal at equilibrium.”SB9
“Equilibrium is balancing chemical equation and the number of atoms of each element is equal before and after reaction.”SB14
“Reaction ends up when it approaches equilibrium. It becomes equal.”SC15
The answers given to the question 2 “What kind of changes occurs in the system when Cl2 gas is added to equilibrium mixture system ?” are given in Table XII.
Table XII. The Categories Belonging The Second Interview Question
Student’s View
A High School
B High School
C High School
Experimental
Control
Experimental
Control
Experimental
Control
The system will shift to the side of consuming Cl2. *
9
75.0
0
0.0
6
50.0
1
8.3
6
50.0
3
25.0
Equilibrium will shift to the products’ side.*
5
41.7
2
16.7
7
58.3
1
8.3
8
66.7
3
25.0
Equilibrium is disturbed.*
3
25.0
1
8.3
3
25.0
1
8.3
5
41.7
1
8.3
Concentration of Cl2 gas will be greater than its initial equilibrium value.*
3
25.0
2
16.7
3
25.0
0
0.0
6
50.0
3
25.0
While the concentration of COCl2 gas has increased. the concentration of CO gas has decreased.
0
0.0
0
0.0
2
16.7
0
0.0
3
25.0
0
0.0
Nothing changes in the reaction.
0
0.0
0
0.0
2
16.7
4
33.3
0
0.0
3
25.0
Cl2 is consumed.
0
0.0
1
8.3
0
0.0
0
0.0
0
0.0
0
0.0
Concentration of Cl2 remains the same.
0
0.0
2
16.7
0
0.0
1
8.3
0
0.0
0
0.0
Reaction decomposes as a substance was added.
0
0.0
1
8.3
0
0.0
1
8.3
0
0.0
0
0.0
Concentration of the substances remains the same.
0
0.0
1
8.3
0
0.0
0
0.0
0
0.0
0
0.0
The amount of COCl2 gas decreases.
0
0.0
1
8.3
0
0.0
0
0.0
0
0.0
0
0.0
The amount of COCl2 and CO gases do not change.
0
0.0
1
8.3
0
0.0
0
0.0
0
0.0
0
0.0
Cl2 gas is a catalyzer. so it is added.
0
0.0
0
0.0
0
0.0
1
8.3
0
0.0
0
0.0
Only the reverse reaction is occurring.
0
0.0
0
0.0
0
0.0
1
8.3
0
0.0
0
0.0
The purpose of this question was to find out the understanding of the students about the effects of concentration on equilibrium reactions. As can be seen in Table XII, correct explanations like “equilibrium is disturbed,” “the system will shift to side of consuming Cl2 gas” and “the equilibrium will shift to products’ side” are a high percentage in the experimental groups. Students who made similar explanations are given below:
“Added gas disturbes the equilibrium. Reaction will shift to the products’ side in order to reduce the effect. As Cl2 gas is added, concentration of Cl2 will increase. The reaction will proceed to remove some of the added Cl2 gas. As a result of this, mole of COCl2 gas increases but mole of CO gas decreases.” SC1
“We can explain this situation according to Le Chatelier’s principle. Reaction adjuts to re-establish equilibrium, so the equilibrium will shift to products to remove the added Cl2 gas.” SA8
“A reaction at equilibrium will proceed in a direction that relieves the stress put upon it. So equilibrium will shift to products.” SB6
From the explanations of students in the control groups, it was determined that a few students made correct explanations such as the “reaction will shift to products’ side,” but they had misconceptions in the concentration of reactives and products with their initial equilibrium value. Some of the answers are stated below:
“Reaction shifts towards products and equilibrium is re-established. The amount of Cl2 will be higher than its initial equilibrium value, but the amount of COCl2 and CO will be the same.” SA14
“Reaction reaches equilibrium again. Concentration of the substances stays the same.” SA20
“Reactants collide to form products, but the amount of Cl2 is the same with its initial equilibrium value. While the amount of CO reduces, the amount of COCl2 goes up.” SB19
Some of the explanations in the control groups are completely far from being scientific and they are all wrong. The expressions in that group are:
“Cl2 is a catalyzer so it is added. It speeds up the reaction.”SB17
“Reaction decomposes as a substance was added.” SA21
The answers given to question 3, “What kind of changes happen in the system when we increase the temperature from 25 ºC to 50ºC?” are given in Table XIII.
Table X1II. The Categories Belonging to The Third Interview Question
Student’s View
A High School
B High School
C High School
Experimental
Control
Experimental
Control
Experimental
Control
The reaction will proceed to use up the added energy.*
6
50.0
0
0.0
5
41.7
1
8.3
7
58.3
2
16.7
The reaction will shift to reactants.*
10
83.3
2
16.7
6
50.0
1
8.3
10
83.3
2
16.7
While the concentration of CO and Cl2 gases increase. the concentration of COCl2 gas decreases.*
3
25.0
0
0.0
2
16.7
0
0.0
0
0.0
0
0.0
Equilibrium is disturbed.*
4
33.3
2
16.7
4
33.3
1
8.3
4
33.3
1
8.3
The rate of the reaction increases.
2
16.7
3
25.0
3
25.0
2
16.7
3
25.0
3
25.0
Equilibrium constant (Keq) changes.
0
0.0
0
0.0
0
0.0
0
0.0
3
25.0
1
8.3
The rate of the forward reaction decreases.
0
0.0
1
8.3
0
0.0
1
8.3
0
0.0
0
0.0
The rate of the reverse reaction doesn’t change.
0
0.0
0
0.0
0
0.0
0
0.0
0
0.0
1
8.3
Reaction ends up faster.
0
0.0
0
0.0
0
0.0
0
0.0
0
0.0
1
8.3
No change happens in the reaction.
0
0.0
0
0.0
1
8.3
2
16.7
0
0.0
0
0.0
Forward activation energy decreases.
0
0.0
0
0.0
0
0.0
1
8.3
0
0.0
0
0.0
Activation energy increases.
0
0.0
0
0.0
0
0.0
1
8.3
0
0.0
0
0.0
Boiling increases.
0
0.0
0
0.0
0
0.0
1
8.3
0
0.0
0
0.0
Concentrations of all species in the reaction mixture increase.
0
0.0
1
8.3
0
0.0
0
0.0
0
0.0
0
0.0
Gases expand and diffuse.
0
0.0
1
8.3
0
0.0
0
0.0
0
0.0
0
0.0
Durability of products is ensured.
0
0.0
0
0.0
0
0.0
1
8.3
0
0.0
0
0.0
The correct answer for this question is that the “reaction will shift to reactants’ side, concentration of reactants increase and concentration of products decrease.” It is understood from Table XIII, there are more students who made correct explanations in the experimental groups than in the control groups. Some of the students who explained similar ideas are stated below:
“As the reaction is exothermic, reaction will shift to use up the added energy, namely the direction of reactants. While the concentration of COCl2 is decreasing, concentrations of CO and Cl2 increase.” SA1
“A reaction at equilibrium will proceed in a direction that relieves the stress put upon it. If temperature is increased, the reaction will proceed to use up the added energy. Because energy is a product. Consequently, reaction shifts towards reactants.” SA5
“Temperature is increased. In such a situation, reaction shifts to the reactants’ side and equilibrium is re-established.” SC3
“If a system is at equilibrium and temperature is changing, the system adjusts to re-establish equilibrium in such a way as to partially counteract the imposed effect. Reaction will shift to reactants’ side.” SB2
It is seen from expressions of students in the control groups that students can explain the relationship between temperature and the rate of the reaction rather than temperature and equilibrium. Also, it was detected from the answers that students have some misconceptions coming from the previous unit of chemical equilibrium. The especially striking answers are below:
“If temperature is increased, that means the energy is increasing. Activation energy goes up.” SB15
“When temperature is increased, reaction will shift to the reactants’ side. Because the rate of the reverse reaction will increase, but the rate of the forward reaction will decrease.” SA13
“As reaction is exothermic, while the reverse reaction speeds up, forward reaction slows down.” SB20
Some of the misconceptions are originally found with this research. These explanations are given below: “Boiling temperature increases. More gas comes up into the air.” SC18
“Temperature is increased. Molarities of all species in the reaction increase because molarity and heat are directly proportionl.”SA21
“Reaction ends up faster because the temperature is increased.”SC19
The answers given to the question 4, “What kinds of changes happen in the system when the volume of the container is halved? are presented in Table XIV.
Table XIV. The Categories Belonging The Fourth Interview Question
Student’s View
A High School
B High School
C High School
Experimental
Control
Experimental
Control
Experimental
Control
Equilibrium is disturbed.*
4
33.3
2
16.7
0
0.0
0
0.0
4
33.3
1
8.3
Reaction will shift to partially restore the original pressure.*
4
33.3
1
8.3
5
41.7
0
0.0
7
58.3
2
16.7
Reaction will proceed to make fewer moles of gas.*
6
50.0
1
8.3
3
25.0
1
8.3
9
75.0
2
16.7
Reaction will shift to products.*
6
50.0
1
8.3
3
25.0
0
0.0
5
41.7
1
8.3
Pressure increases.
7
58.3
4
33.3
5
41.7
2
16.7
9
75.0
4
33.3
While the mole of CO and Cl2 gases decreases. the mole of COCl2 gas increases.
2
16.7
0
0.0
0
0.0
0
0.0
0
0.0
0
0.0
Equilibrium will proceed to make more moles of gas.
0
0.0
0
0.0
0
0.0
0
0.0
0
0.0
1
8.3
Air pressure becomes equal with the pressure of the chemical substances.
0
0.0
0
0.0
0
0.0
1
8.3
0
0.0
0
0.0
If there is a catalyzer in reaction. The rate of reaction is increased. otherwise it will be initially unchanged.
0
0.0
0
0.0
0
0.0
0
0.0
0
0.0
1
8.3
When the volume decreases. mole of gases decreases. too.
0
0.0
0
0.0
0
0.0
0
0.0
0
0.0
1
8.3
No change occurs in the reaction.
0
0.0
3
25.0
1
8.3
3
25.0
0
0.0
1
8.3
Reaction decays.
0
0.0
1
8.3
0
0.0
0
0.0
0
0.0
0
0.0
As can be seen in Table XIV, both students in the experimental groups and the control groups can construct a bridge between the concepts of volume and pressure. On the other hand, a few students in the control groups made correct explanations about the effects of volume on equilibrium reactions. Some of explanations in the experimental groups are stated below:
“This is a prediction made by Le Chatelier’s principle. When volume is decreased, pressure is increased. Reaction will shift as to partially restore the original pressure. Namely, it will proceed towards the side with fewer moles of gas. As time goes on, while CO and Cl2 reactants are produced, COCl2 is consumed. As a result of this, moles of reactants are decreased, mole of product is increased.” SA4
“We look at the mole of the reactants and products. There are two moles of gas particles on the left hand side of the reaction and one mole of gas particle on the right hand side of the reaction. Decreasing the volume increases the pressure. Reaction will shift to fewer moles of gas to reduce the pressure. It will shift to the products’ side.” SB3
“Maximum entropy and minimum energy are important for reaction. The two tendencies oppose each other at equilibrium. If a system has reached equilibrium it will remain at equilibrium. When equilibrium is disturbed, the equilibrium position will shift in the direction which tends to minimize the effect of the disturbance. Reducing the volume of this equilibrium system is equivalent to increasing the pressure. Equilibrium will shift to fewer moles of gas.” SC5
It is understood from these expressions that students in the experimental groups can explain the effects of volume on the equilibrium reactions correctly.
It can be seen that many students in the control groups explain relationship between pressure and volume instead of the effects of volume on equilibrium reactions. Besides scientifically correct explanations, the incorrect ones are also striking. Some of the students’ answers are as follows:
“Nothing changes as there is a reaction between these chemicals. These substances are the components that are not affected by volume change.” SA18
“As, the number of atoms of each element is equal before and after reaction, volume change won’t affect this.” SC22
“There is the equivalence of air pressure with chemical pressure.” SB13
“Gases are compressible, pressure is increased, reaction decays.” SB10
The answers given to the question 5, “What is Le Chatelier’s principle?” are presented in Table XV.
Table XV. The Categories Belonging to the Fifth Interview Question
Student’s View
A High School
B High School
C High School
Experimental
Control
Experimental
Control
Experimental
Control
When a system at equilibrium is disturbed. the system will shift its equilibrium position in the opposite direction*
8
66.7
0
0.0
3
25.0
0
0.0
5
41.7
0
0.0
Equilibrium tends to compensate for the effects of disturbance.*
3
25.0
1
8.3
3
25.0
0
0.0
5
41.7
0
0.0
It expresses how the system will reach equilibrium again when the equilibrium is disturbed*
3
25.0
1
8.3
2
16.7
0
0.0
4
33.3
2
16.7
When reagents are added or the temperature or pressure is changed at equilibrium. equilibrium position will shift to which direction.*
0
0.0
0
0.0
3
25.0
0
0.0
0
0.0
0
0.0
It gives information about the reaction.
0
0.0
0
0.0
0
0.0
0
0.0
0
0.0
3
25.0
It is a chemical event.
0
0.0
0
0.0
0
0.0
2
16.7
0
0.0
0
0.0
It explains the relationship of pressure-volume-mole in gases.
0
0.0
0
0.0
0
0.0
2
16.7
0
0.0
1
8.3
It is the principle that explains the relationship between the reaction and equilibrium constant (Keq).
0
0.0
0
0.0
1
8.3
0
0.0
0
0.0
0
0.0
It is the balancing chemical equation.
0
0.0
0
0.0
0
0.0
1
8.3
0
0.0
0
0.0
It is a principle related to the electrons surrounding the atoms.
0
0.0
0
0.0
0
0.0
1
8.3
0
0.0
0
0.0
It is the principle that determines the mole.
0
0.0
0
0.0
0
0.0
1
8.3
0
0.0
0
0.0
It explains that the mass of the products by a chemical reaction is always equal to the mass of the reactants.
0
0.0
0
0.0
0
0.0
1
8.3
0
0.0
0
0.0
It is a principle about the equilibrium mixture.
0
0.0
0
0.0
0
0.0
0
0.0
1
8.3
0
0.0
It is a gas law.
0
0.0
1
8.3
0
0.0
0
0.0
0
0.0
0
0.0
In this question, the students were supposed to describe Le Chatelier’s principle in their own words. The students are expected to answer that question, “if a stress is applied to a system at equilibrium, the system will adjust so as to partially relieve the stress.” The word stress here means any disturbances to equilibrium, such as temperature, pressure or concentration. When Table XV is analyzed, it seen that most of the students in the experimental groups explain Le Chatelier’s principle correctly. Some of the answers that the students in the experimental groups are given below:
“If a system has reached equilibrium it will remain at equilibrium. Since maximum entropy and minimum energy are compatible with each other at equilibrium. Equilibrium system tends to compensate for the effects of disturbance. For example, if one of the reactants is added to equilibrium mixture, equilibrium will shift to products’ side to use up the added reactant.” SC5
“When equilibrium is disturbed, the equilibrium position will shift in the direction which tends to counteract the effect of the disturbance. For example, if a substance is added, the equilibrium position shifts to use up the added substance.” SA4
“It explains that whether the reaction will shift to the products or reactants. When a system at equilibrium is disturbed, the system will shift its equilibrium position in the opposite direction. It states that when reagents are added or the temperature or pressure is changed at equilibrium, equilibrium position will shift to which direction.” SB7
It is especially seen from these explanations in the control groups that the students confuse Le Chatelier’s principle with the other principles and laws in chemistry such as the conservation of mass, Gay Lussac’s law, Charles’s law and Boyle Mariotte’s law. Some of the expressions are below:
“We balance chemical equations according to this principle. The same number of atoms of each element appearing in reactants must appear in the products.” SB13
“It is one of the principles in chemistry. It explains that the mass of the products by a chemical reaction is always equal to the mass of the reactant.” SB15
“It is the principle that determines the mole of the atom.” SB18
“It is a principle showing the relationship between pressure, mole, volume and the temperature of the gases.” SC22
Some of the explanations are completely far from being scientific and they are all wrong. The expressions in that group are as follows:
“It is a principle related to the electrons surrounding an atom.” SB21
“It determines the reactions between molecules.” SC23
“It is a principle about equilibrium mixture.” SB22
