I observed three of Mr Humour’s lessons. They covered reversibility of reactions, Le Chatelier’s principle and the equilibrium constant.
Lesson 1(45 minutes): Reversibility of reactions
Mr Humour started the lesson by explaining that my critical friend and I were conducting research on how he taught the topic, chemical equilibrium. He assured the learners that they did not need to be overly concerned about our presence as the study was targeted at him as the ‘rat’ under investigation. The students found this amusing and it helped to make the atmosphere more relaxed.
The lesson was on reversibility of reactions and the teacher introduced the lesson by tapping into the learners’ prior knowledge. The learners had already studied reversible reactions in Grade 9, which the teacher was aware of. So, he started off by enquiring “Today’s lesson is reversible
reactions. Ok, reversible reactions, reversible reactions. Is there anybody who recalls a
reversible reaction from Grade 9?” One of the learners correctly responded ‘A reaction in which reactants can form a product and products can react to form reactants’. He continued to ask the
learner for an example and the learner said ‘Ammonia which is formed from nitrogen and
hydrogen’. All through the lesson, the teacher integrated learners’ prior knowledge when he
explained concepts. By analysing the learners’ responses, I concluded that their everyday prior knowledge concerning reversible reactions was scientific and accurate.
Similar to Mrs Focus, most of teacher-learner interactions consisted of question and answer exchanges as exemplified by the following:
55 E1:T2L1
“T2: Is this a gaseous reaction?
L: Yes
T2: How do I balance it?
LLL: Put a 3 in front of H and 2 in front of N.
T Wow, yes put a 3 here and a 2 here”
A number of times the learners chorused the answers as most questions were closed and did not require in-depth explanations.
Similarly, Mr Humour used various analogies when mediating the topic. He described reversibility as similar to students entering and leaving a school by expressing,
“Suppose here at school every time you were getting ready to leave and go to another
school, there was another student coming in, we would sent another student to immediately come in”.
The teacher also used the pumping of water in a swimming pool as an illustration of a system at equilibrium by informing the class.
The water is pumped, is circulated, again it is pumped, and its circulated and keeps being pumped and comes back and pumped out…….So I am saying technically, the water stays the same although there is water coming in and water going out. So we say when we have such a system, we say the rate of the forward reaction is equal to the backward reaction.
He further explained Le Chatelier’s Principle by comparing to the body in this way “let’s talk
about your body, have you ever, eh eh eh, swallowed something that’s not good for your body? What does your body do? You feel sick isn’t it?” He continued “that’s you reacting. That’s your body trying to counter the wrong thing that you have put in up there. So your body starts
sweating or you start having a running tummy or you start other things, having fevers and so on. It’s our natural LCP”.
In addition, Mr Humour gave detailed and occasionally lengthy explanations of reversible reactions and made use of several examples. These included the production of ammonia and hydrogen iodide. When clarifying these concepts, he wrote the main points and chemical equations on the board. He would ask questions on how to balance the equations. Mr Humour’s explanations were very accurate reflecting a sound subject matter knowledge and mastery of the language of instruction. He even ‘borrowed’ some terms from Physics to compare the difference between dynamic and static equilibrium. This confirmed that Physics is closer to his heart as well as reflecting integration within the same subject.
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The learners seemed to have difficulty in understanding why not all reactions were reversible as typified by one question “could water be a reversible reaction when it decomposes?” The teacher handled this difficulty by clearing up “No, no, the reaction between the oxygen and
hydrogen is one directional equation. Hydrogen and oxygen you get water”. There was also a
concern on when reversibility occurs as the same learner asked “Does it occur when products
are decomposing naturally?” However, there was no feedback from the teacher to address this
question.
Furthermore, the learners found the concept of an increase in concentration to be problematic. The teacher explained that if you increase the concentration of one of the reactants the forward reaction is favoured. He used the production of hydrogen iodide and expounded that an increase in hydrogen will cause the forward reaction to be favoured. The learners did not agree and
argued that this was only possible if iodine was also increased. One learner correctly pointed out:
But sir, with the equation you gave us, that if you pump in more hydrogen then the forward reaction will increase, but wouldn’t more iodine be required as well, because for that as well the amount of iodine must increase.
This issue caused a considerable amount of debate until the teacher concluded the discussion by stating “our theory just accept, let’s take an ideal situation where there is enough iodine”. The learners were not completely satisfied with and one learner responded “sir, will we be tested on
this?” This was greeted by laughter from the other learners. Lesson 2 (45 minutes): Le Chatelier’s Principle
Mr Humour began the lesson by reminding the learners what he had taught them in the previous lesson. He repeated in detail the effects of temperature on the ammonia equilibrium. The lesson was on the effect of concentration, pressure and a catalyst on an equilibrium system.
Mr Humour employed mainly the lecture, question, and answer methods as his teaching strategies. Comparable to Mrs Focus, he used short answer questions and probing as a way of scaffolding the learners to make sense of concentration. As a result, the teacher-learner interactions consisted of question- answer dialogues such as:
E2: T2L2
“T2: If you increase the amount of concentration of nitrogen gas, what do you think will happen? Describe in full.
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L1: We will increase the concentration of hydrogen.
T2: How do we do that, how will that affect equilibrium, describe in full. L1: More nitrogen will be used.
The preceding conversation highlights one of the problems encountered during the lesson. The teacher and the learners frequently did not seem to follow each other. The learners would give answers appearing to be tangential to what the teacher required. All the same, the teacher continued to probe until they reached a common understanding. Sometimes they would make contradictory statements when answering questions as one learner said “more ammonia will be
produced, because the backward reaction will be favoured to make more ammonia” instead of
the forward reaction is favoured.
The terminology used during the lesson was a source of difficulty for some learners as illustrated by this question which was asked at the end of the lessons “sir, what does it mean when you say
a reaction is favoured?” The teacher addressed such language concerns by explaining further.
However, there were instances when prior knowledge was a hindrance to learning as reflected in Fig 4.7 below.
Fig 4.7: Shows an example of a learner who struggled with explaining changes in equilibrium because they misapplied the collision theory
58 Lesson 3 (45 minutes): The equilibrium constant
This lesson was on the equilibrium constant. Mr Humour commenced the lesson by discussing the concept of the equilibrium constant. He explained the equilibrium constant in words as a’
comparison of the concentration of the products raised to their powers and the reactants raised to their number of moles’. Using symbols he wrote on the chalkboard:
‘K= [products]x
[reactants]
Firstly, he used a general equation to show how to work out the equilibrium constant and then he went on to use the hydrogen iodide equilibrium by stating “Suppose hydrogen reacts with iodine gas this way and give us, the equilibrium balanced, whilst writing H2(g) + I2 to give 2HI(g.) He continued K expression or the equilibrium expression would be HI to the power of 2 divided by
the power and to the power and indicated on the whiteboard that K would be equal to [HI]2
[H2][I2]”
He pointed out that “the squared brackets mean the concentration of the species”.
Similar to the previous lessons, the whiteboard and a worksheet were the LTSMs. Mr Humour made effective use of the whiteboard by writing neatly, clearly and in an organised manner. One could easily follow the progress of the lesson by looking at what was written on the board. He also left the main ideas visible for the duration of the lesson as shown in Fig 4.8.
Fig 4.8: A snapshot showing an example of the effective use of the whiteboard by Mr Humour
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Mr Humour also pointed out the significance of a large value of the equilibrium constant by suggesting that it meant “the forward reaction is favoured and it has gone too far compared to
the backward reaction. If K is large the reaction has gone so far, that the concentration of the denominator is so small”.
Mr Humour utilised the question and answer method, whole class discussions, demonstration, group work and one-on-one consultation as teaching strategies. He used different examples to demonstrate how to calculate the equilibrium constant and deduce its units. Mr Humour asked the students to work out some examples from their booklet while he moved around assisting the learners as shown in Fig 4.9.
Fig 4.9: An example of questions answered by learners during the lesson.
He continually urged the learners to work together as he walked around attending to individual learners. The learners would work through a question and if there were common problems, he would explain the question on the chalkboard.
In this lesson, some learners found it difficult to understand the significance of the magnitude of the equilibrium constant. Mr Humour attempted to assist learners to comprehend by using another description. One learner kept asking what an equilibrium constant equal to one meant. It appeared the learner found the explanation to be unsatisfactory as presented by her body
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Other learners failed to find the units of the equilibrium constant, as they were not proficient at using indices. Mr Humour attempted to go back to the laws of indices assisting some learners but not all. Similarly, the learners struggled with one question involving a solid in the chemical equation. Mr Humour helped the learners by articulating ‘Oh, yes, there is something I forgot to
mention, solids and liquids do not appear in the equilibrium expression’.
Best practices and missed opportunities for lessons 1-3
As with Mrs Focus, Mr Humour gave accurate explanations of the equilibrium concepts. He mentioned one analogy after the other. For the duration of his lessons, he made effective use of the whiteboard. The exercises given to the learners contained a variety of examples covering all aspects of a particular idea. This exposed the learners to the different types of possible
examination questions. Mr Humour made sure he revised the questions with the learners to correct any misconceptions as shown in Fig 4.9.
Fig 4.10: An example showing an exercise given during a lesson and how the learner corrected his answers after discussion with the teacher
However, Mr Humour, like Mrs Focus, could have given the learners more opportunities to talk. There were instances when a point generated some debate but Mr Humour would quickly move on to answer the question stalling the conversations. Equally, there were some points; I thought he should have explained further. These include, limiting reagents and an equilibrium constant
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of one. In my opinion, learners were not as actively involved as they could have been. Integrating more of learners’ prior knowledge, practical activities and varying teaching strategies, might have improved learner involvement.
4.5 Interviews
In this study, I carried out four interviews, two before the lesson observations and two after. The aim of the pre-interview was to answer my first research question, namely, what are the
teachers’ views and experiences of teaching the topic on chemical equilibrium? The post- interviews were used to solicit additional information, seek clarification as well as a data validation tool.