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Energetics Thermochemistry

Mr Khemistry

Energetics Thermochemistry

Energetics is such a broad topic students sometimes have difficulty understanding what the question is asking for. This post aims to help build a mental shortcut for students to “funnel” the question into broad question types. Thereafter to quickly apply the thought process for solving it.

In the picture below, you see the four broad question structures on the left. On the right side is the approach to solve certain types of questions. Additionally, there are also acronyms to help students remember the sequence of answer, e.g. F.A.I.L for Born Haber Cycles and BE.R.P. for bond energy.

Energetics Question Structure

Energy cycles can only be done well if you have a good grasp of the common definitions of different enthalpy change. Point 5 on the left shows the three main components of definitions for enthalpy change.

Energy level diagrams are simply a special type of energy cycle where the arrows point upward for endothermic reactions and downwards for exothermic reactions. Learn how to construct energy level diagrams quickly in our weekly classes. It is easier to learn how to construct energy cycles/levels when you can see how other students do it. Moreover, we can also see what kind of mistakes are commonly made.

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Cells of recognition

Mr Khemistry

Cells of Recognition

All of us have brain cells that helps us make sense of our environment. From the second we blink-open our eyes when we wake. These cells of recognition have been built way back when we were infants. Day by day, week by week, month by month and year by year. We are able to go through the day, sometimes without thinking much about what we’re doing because of them. Some experts call this habit. But before we can form a habit, we do need to think about what we’re doing. Only once we have made sense of the action, then we do it repeatedly WITHOUT thinking about it.

Why am i talking about this?

Because i believe the reason why many students do not do well with Chemistry (or any subject) is due to the fact that they don’t recognize this. Some do and they actively build cells of recognition as they are studying. That is the reason why we do Ten Year Series. To build cells of recognition. To see how Cambridge phrased the questions SO THAT we can recognize the pattern and give the correct answer. What we should try to do is to inculcate this routine into our daily studying.

How many of you realized that the duration that you have to learn more complex concepts is getting shorter? In primary school, you had six whole years to learn and build those cells of recognition. For secondary school, you had four whole years. However, in Junior College, you have slightly less than two years to make sense of the most abstract concepts!

Is it any wonder that students are struggling? Does it seem strange that you are failing tests where previously you have always done well? The  change in teaching and learning environment from classroom teaching to lecture/tutorials. You were expected to hit the road running. Many students find themselves wondering what happened. The truth is, even though humans are extremely adaptable creatures, we still need time to process changes and to adjust our thinking.

In primary school, we had six years to adjust to the concept of “School”. At secondary level, we had four years to make sense of many subjects at introductory level. For Junior College, we have slightly less than one and the half years to complete the “advanced” syllabus. To adjust to the new system of lecture/tutorial, for some, it’s also a period where they are exploring romantic relationships. With so many changes going on at the same time, it’s no wonder many youths cannot cope with their studies load.

How do we navigate this tumultuous times? By actively thinking and planning our time weekly, having a good overview of what we are doing. It helps when you can build up a routine for quickly reviewing and reflecting on the boatload of new content every week. The students who can adapt quickly to the changes and settle down to building new cells of recognition will do well. Those who take a long time to adapt will show symptoms, such as late-coming and lethargic behavior in class.

It’s vitally important that students make full use of their weekends to recap what they have learnt through the week. The many requirements imposed on them throughout the week can drain their energy, causing them to be too tired to revise at night. Those who force themselves to stay up late to study more often then not, put too much stress on themselves. Usually this results in lowered alertness and attentiveness during lesson time, which hinders their ability to take in new information. Not having adequate rest during the weekdays is detrimental to  learning.

In a nutshell, build routines quickly, then build cells of recognition. This process will allow you to quickly adapt to JC life and get down to learning the new concepts.

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Chemical Equilibrium Summary Table

Mr Khemistry

Chemical Equilibrium Summary Table

The qualitative aspect of Chemical Equilibrium can be summarized into the table below.

From the table, we can see that changes in concentration, pressure and catalyst does not affect Kc/Kp. The only factor that does affect equilibrium constants is temperature. Also, we would need to know whether the forward reaction is endo or exothermic to predict the effect temperature change will have on it.

Note that increasing temperature increases both the rate of forward and backward reactions. However, the rate of the endothermic reaction will be increased more than the rate of the exothermic reaction.

If the enthalpy change for the reaction is zero, temperature will have no effect on the equilibrium. Similarly, if the reaction has the same number of moles of gaseous particles on both sides, pressure will have no effect on it.

An interesting point to note is catalysts have no effect on position of equilibrium and equilibrium constant. The only effect it has is to increase the rate of both forward and backward reactions to the same extent.

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Relationship between Kc and Kp – Chemical Equilibrium

Mr Khemistry

Relationship between Kc and Kp – Chemical Equilibrium

I was updating the chemical equilibrium notes this week and thought it would be good to share this with all of you.

Didn’t know how Kc and Kp was related and i was stumped by a question about 10 years ago when i was still teaching in a JC.

Relationship between Kc and Kp

The main idea is to use the ideal gas equation to substitute partial pressures in concentration terms.

Once you got it, it’s quite easy to remember 🙂

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Comparison between Galvanic and Electrolytic Cell

Mr Khemistry

Comparison between galvanic and electrolytic cell table

Students tend to get mixed up between the two types of electrochemical cells. This table will illustrate the comparison between galvanic and electrolytic cell.

A useful acronym, P.A.N.I.C. for electrolytic cell polarity (Positive is Anode Negative is Cathode). Then just remember polarity is reversed for galvanic cell.

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Physical Chemistry Calculations – Be Aware Where Errors Occur

Mr Khemistry

Physical Chemistry Calculations

Physical Chemistry – Recently i was revising acid-base equilibrium with one of my students and i realised she has trouble getting the right answer even though the procedure is correct. We went through the process and every step was conceptually correct. Then i got her to show me how she calculated on her GC, i saw the workings and it was right. But when she pressed “=”, the answer came out wrong!

Boy, was i puzzled. We went through the steps carefully again and still we arrived at the same outcome. Finally, after i queried her on one of the steps, we both realised what’s wrong. She did not use brackets to sequence the operations, thus the calculator did not process the workings in the sequence we wanted.

A few more questions with calculations we encountered different problems, like missing out a zero or misreading a digit. I pointed out to her none of the questions we did had any mistakes conceptually, only the numerical answers were wrong. I asked her would she be discouraged and come to the conclusion physical chemistry is difficult? She said yes. And no wonder, after thinking so hard and so many calculations, the final answer always turned out to be wrong.

I taught her to carefully check through her workings when doing calculations and look out for common errors. Most importantly, not to be discouraged and come to the wrong conclusion physical chemistry is hard! Most of the calculations in physical chemistry is NOT hard, we just need to practise and look out for common errors.

Do you find physical chemistry daunting? You can do well in it!

Come join us at our weekly group tuition to see how you can confidently approach calculations too!

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Chemistry Tuition by Mr Eric Kua

Mr Khemistry

Chemistry Tuition by Mr Khemistry

Looking for a good, reliable Chemistry Tuition? We understand there are many centers that offers Chemistry Tuition nowadays and it’s difficult to tell which ones are worth your time. Here we compile a list of reasons why Mr Khemistry is the Chemistry Tuition you are looking for.

  1. We are Qualified. Our Principal Tutor, Mr Eric Kua, graduated from NUS with a Degree majoring in Chemistry. He has taught in a JC for more than 8 years. For his full academic and teaching qualifications, click here.
  2. We are Experienced. All our tutors have over 10 years of experience tutoring students in Chemistry, Mr Eric Kua has more than 13 years of experience in Chemistry tuition.
  3. We are Committed. Our goal is the same as yours, to unlock the potential that is in every student. We offer unlimited consultations via whatsapp and revision crash courses during holiday period to bring every student up to speed.
  4. We are Specialists. Our focus on Chemistry allows us to hone our pedagogy in this subject to a much greater depth. Think about why we visit specialists in hospitals. Yup.
  5.  We are Accessible. Our locations are conveniently located within walking distance from MRT stations (Beauty World and Bishan).

Pre-qualification

After many years of tutoring students from different ability levels, there is some common characteristics of students who are likely to benefit from attending group lessons with us. Here are some for your consideration.

  • They are consistent. They do not skip lessons to attend birthday parties. If they have important appointments that clashes, they will endeavor to go to another class for make-up lesson.
  • They are willing to put in effort after lesson to revise their work. We give additional practise for the students, those who improve dramatically are usually the ones who take the time to attempt these extra practise and consult the tutor when they are unsure.
  • They do not attend more than two tuition every week. Attending more than two tuition lessons every week saps their energy and takes away revision time. More likely they are using it as a clutch rather than a real need.
  • They reflect and THINK about what are the main concepts after lessons. Students who simply take everything at face value without thinking, memorizing their notes, are unlikely to excel in Chemistry at A levels. A simple test would be to look at their summarized notes, a student who has thought through would organize his/her notes quite differently from one who merely copy and paste from lecture notes.

Remember, it takes two hands to clap. You can engage the best Chemistry tutor but if you do not do your part, the results are unlikely to change. We will provide concise illustrated notes with clear teaching, putting the best resources at your disposal, what you do with it will determine the outcome.

Born Haber Level Diagram

Mr Khemistry

Born Haber Level Diagram

Born Haber Level Diagram

Always start your cycle at datum line, i.e. at zero enthalpy. Tip: You may combine the ionisation energies for Fe or for other metals.
Multiple electron affinities can also be combined.

Take note that for energy level diagram, you will have to show the ionized electrons from Fe. When you use bond energy instead of enthalpy of atomisation, you will need to multiply by the correct coefficient. Lastly, don’t forget to put your state symbols! 🙂

Hope this has been useful for you, if you wish to learn how to draw the diagram using energy cycle, go here.

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Born Haber Cycle

Mr Khemistry

Born Haber Cycle

Born Haber Cycle Diagram

Born Haber Cycle

Using the acronym F.A.I.L. where F stands for enthalpy change of formation of the ionic compound, A stands for atomisation of the constituent elements and I stands for ionisation of cation and anion and L stands for Lattice Energy.

We have four major components and this energy cycle is easy to draw with no worries about which species having a higher energy level. There is no need to include electrons as they are immediately used to form the anion.

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