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Let’s add nitrogen gas

elements110007
‘Nitrogen’ page from Theodore Gray’s amazing book, ‘The Elements’

Initial conditions

Recall from last week that our Periodic Table Smoothie contains the following species:

Substance Amount present (moles)
He(g) 1.00000
Be(s) 0.51435
LiH(s) 0.27670
Li2C2(s) 0.27165
B2H6(g) 0.23300
Be2C(s) 0.17470
H2(g) 0.14267
BeC2(s) 0.13625
CH4(g) 0.00949

Pressure: 718 kPa
Temperature: 350 °C

Reactions of nitrogen in our 10-litre vessel

Our freshly-added 1.00 mol of nitrogen gas, N2(g), reacts with hydrogen gas to make ammonia in the following reversible (equilibrium) reaction. We will assume that the interior metal surface of the vessel is a suitable catalyst for this reaction (e.g. iron). 

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There are three other reactions below that might have occurred at higher temperature, but I’ve chosen not to raise the temperature of the vessel at this point. Rather, we’ll keep it at 350 °C to keep things manageable.*

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*I was tempted at this point to elevate the temperature of our vessel to 500 °C so that the second reaction could take place as well. This would produce copious amounts of smelly ammonia gas, which would allow for larger quantities of interesting organic compounds to be produced later on. To keep our simulation safe and (relatively) simple, I’ve decided to keep the vessel at 350 °C. Interesting compounds organic will still form – only in smaller amounts.

Equilibria

The ammonia reaction above (the first equation) is actually an equilibrium reaction. That means that the reactants are never completely used up, and the yield is not 100%.

Recall from Le Châtelier’s principle that removing product from an equilibrium reaction causes the position of equilibrium to shift to the right, forming more product. This is because:

“If an equilibrium system is subjected to a change, the system will adjust itself to partially oppose the effect of the change.” – Le Châtelier’s principle

There are three reactions that will remove ammonia from our vessel while it’s being produced, and I’ve put all three of these into the simulation. One of these is the reverse of the reaction above (producing hydrogen and nitrogen gases) and the other two are described below. Let’s take a look at those other two reactions.

With what will the ammonia react in our vessel?

Ammonia can undergo the following reactions with the other things in our vessel**

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**The ammonia does react with methane and beryllium as well, but only at temperatures of 1200 °C and 600 °C, respectively.

Two compounds will be formed: lithium amide and borazine.[1] Lithium amide reacts with nothing else in the vessel, so the reaction chain stops there. Borazine, on the other hand, is much more interesting.

We’ve made borazine!

Borazine is a colourless liquid at room at temperature. It boils at 53 °C and has a structure that resembles that of benzene.

200px-borazine-dimensions-2d
Borazine is isostructural with benzene
Because of the electronegativity difference of about 1.0 between the B and N atoms in the ring, borazine has a mesomer structure:

600px-borazin_mesomers

Like benzene, there is partial delocalisation of the lone pair of electrons on the nitrogen atoms.

Borazine polymerises into polyborazine!

Fascinatingly, borazine polymerises into polyborazine at temperatures above 70 °C, releasing an equal number of moles of hydrogen gas.[2] Polyborazine isn’t particularly well-understood or well-documented, but one recent paper suggested it might play a role in the creation of potential ceramics such as boron carbonitrides. Borazine can also be used as a precursor to grow boron nitride thin films on surfaces, such as the nanomesh structure which is formed on rhodium.[3]

Like several of the other compounds we’ve created in our Periodic Table Smoothie, polyborazine has also been proposed as a hydrogen storage medium for hydrogen cars, whereby polyborazine utilises a “single pot” process for digestion and reduction to recreate ammonia borane.

polyborazylene_polymer
Polyborazine’s chemical structure
The hydrogen released during the polymerisation process will then react further with a little bit of the remaining nitrogen to produce a little more NH3(g) – but not much. Recall from earlier that the ammonia reaction is an equilibrium one, and the yield of NH3(g) at pressures under 30 atmospheres is very low. Pressure in our vessel is still only around 7 atmospheres.

Simulation results

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Once polymerised, this would form about 12 grams of polyborazine:

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As far as I’m aware, no further reactions will take place in the vessel this week.

Conclusion after adding 1.00 mole of nitrogen gas

Substance Amount in mol
He(g) 1.000
Be(s) 0.514
LiH(s) 0.000
Li2C2(s) 0.272
B2H6(g) 0.000
Be2C(s) 0.175
H2(g) 0.007
BeC2(s) 0.136
CH4(g) 0.009
N2(g) 0.552
NH3(g) 0.154
LiNH2(s) 0.277
polyborazine 12.194 grams

Pressure: 891 kPa (higher than before due to the addition of nitrogen gas)
Temperature: 350 °C (vessel is still being maintained at constant temperature)

Next week, we’ll add a mole of oxygen gas to the vessel. Warning: it might explode.

References

  1. Stock, Alfred and Erich Pohland. “Borwasserstoffe, VIII. Zur Kenntnis Des B 2 H 6 Und Des B 5 H 11”. Berichte der deutschen chemischen Gesellschaft (A and B Series) 59.9 (1926): 2210-2215. Web.
  2. Mohammad, Faiz. Specialty Polymers. Tunbridge Wells: Anshan, 2007. Print.
  3. Toury, Berangere and Philippe Miele. “A New Polyborazine-Based Route To Boron Nitride Fibres”. Journal of Materials Chemistry 14.17 (2004): 2609. Web. 4 May 2016.

“Soluble or Not?” Chemistry Flashcards

Soluble or Not? Flashcards. Click to buy
Soluble or Not? Flashcards. Click to buy

Solubility rules are among the most important things you’ll need to memorise in your VCE Chemistry studies. There are two main ways to get this done: either learn a set of rules or memorise all the compounds you need by themselves. I use a mixture of these two methods to figure out whether a compound dissolves in water or not.

Test your students (or yourselves) with a set of Soluble or Not? flashcards. Each flashcard has a commonly-used compound on the front (e.g. Zn(OH)2) and the word SOLUBLE or NOT on the back.

There are three ways to use these cards.

1. Name the compound.

Present the cards to the student white side up. The student should state the full name including Roman numerals (e.g. iron(III) oxide) as quickly and accurately as possible.

2. State the formula.

Present the cards red/green side up. The student should state the chemical formula of each compound accurately. This step also serves as a primer for the next stage, which requires students to know whether each of these compounds is soluble. The solutions are visible during this step of the game.

3. Soluble or Not?

Present the cards white-side up again. Ask the student to separate the cards into two piles (“SOLUBLE” and “NOT”) without turning them over. At the end, collect all the cards, turn them all over and review the ones that were incorrect. Repeat weekly until the student can get all of them right.

This is where you might want to buy your own set of cards. I’ve hand-picked compounds that come up frequently in VCE examinations from units 1-4, and these will help you focus your learning.

CLICK HERE to buy your set of 20 Soluble or Not? flashcards for A$25.00 with free international shipping.

Create a 2m² Study Space at Home

Source: Maroon White, FSU

Choose a space, at least two square metres in area, where you will do nothing but study. It should be located in a bright, warm, comfortable part of your home with very few distractions. It should be a space that faces a wall or a window, and should not be in the middle of a room where other people might continually walk by. When I say “study space”, I’m referring to a high desk (for good posture), a hard chair (to help you concentrate) and the space that immediately surrounds them.

Remove every object from that 2m² space. If the desk has drawers, empty them. Clean the desk and its surroundings and remove all distractions from nearby (such as a TV, a radio or a buzzing light).

Place only study-related objects in your study space. Textbooks, files, notebooks and plain paper should all be on the desk. Stow the computer away while you’re studying, and only get it out when you need to write an assignment. Because the vast majority of your reading should be done from textbooks, your computer should not be a permanent fixture in your study space. Shut it down and keep it away.

By this point, your study space should look something like these:

Notice how libraries provide you with exactly this type of space? This is the ideal study space: clean, quiet, purpose-built and distraction-free. Source: NYU

Many people say they can’t study in their bedroom. Studies have shown that geographical separation between work and play puts people in the right mindset to do both. Therefore, studying at the same desk that you use to play computer games could be a huge hindrance to your studies. The minority of people who can study in their bedroom have made it a “study space” instead of a place to relax and play.

I study best in libraries because being surrounded by other studious people helps to keep me motivated! Libraries in the UK are strictly silent – so even if your friends are there, they can’t distract you. Natural-looking light fixtures in my Cambridge college library also kept me alert late into the evening while I worked. Find a 2m² study space in your home and make it look like a library. Or, of course, study in your nearest library!

Here are those points again, summarised:
1. Choose at least 2m² in your house as a designated “study space”.
2. Add a high desk and a hard chair;
3. Clean the desk, chair and surroundings;
4. Only put study-related items in that space;
5. Never do anything except for study in that space;
6. Keep your study space immaculately clean and tidy.

Help! My exam is in 3 days’ time and I haven’t studied for it. What should I do?

jameskennedymonash Beat Exam Stress

First, relax.

The priority at this late stage is that you enter the examination hall well-rested, well-fed and with an appropriate level of stress.

1. Sleep early every night

  • Go to bed before 10pm (or 9pm with an exam the next day)
  • Wake up naturally. If you’re waking up too late, go to sleep at 7pm.
  • Avoid backlit screens for one hour prior to sleeping. Backlit screens emit light in the 484-nanometre range, which excites melanopsin in the retinal ganglion cell photoreceptor. This disrupts your circadian rhythm and keeps you awake!

2. Eat healthily

  • Eat regular meals at regular times.
  • Eat plenty of fruit. (Five per day.)
  • Drink plenty of water.

3. Get some lighter exercise

  • Avoid exhausting sports around exam time (e.g. rugby).
  • Do more walking, jogging, and lighter sports at exam time (e.g. badminton).
  • Drink plenty of water(!) Aim to drink 3 litres per day.

Research has shown that you perform difficult tasks (such as a Chemistry exam) much better under moderately relaxed conditions. The famous Yerkes-Dodson curve illustrates this beautifully.

The Yerkes–Dodson law is an empirical relationship between arousal and performance level. Source: Uni of Minnesota
You want to be on top of that blue curve.

More information about the Yerkes-Dodson curve.

Light exercise will help you to position yourself at the tip of that blue curve, which will optimise your state of mind for learning as much as possible in the few days you’ve got left.

Second, do targeted revision.

4. Mise en place (get everything ready)

5. Spend 3½ hours doing a practice examination

  • Spend 3½ hours doing the exam in semi-exam conditions.
  • Mark it immediately afterwards.
  • Keep it for next time: you’ll use the incorrect questions to guide your theory revision (step 6).

6. Spend 3½ hours reading & annotating your textbook

  • Read and annotate the textbook chapters relating to questions you got wrong.
  • DON’T READ YOUR NOTES. Read the textbook instead: it’s much clearer.
  • Re-do those questions now you’ve learned the theory behind them.
  • Follow steps 1-4 on How to use a Textbook: 6 Rules to Follow. This includes making vocabulary lists and beautiful, clear theory notes to go on your wall.
  • Repeat steps 5 and 6 (in this article) every day. (Study at least 7 hours per day.)

Finally, get help.

7. Get help!

  • Contact your teacher with any questions you have; exam content you don’t understand or worries you have about the exam.
  • Talk to a friend if you’re stressed about the exam.
  • Check out the resources below if your stress levels are still too high.

8. More resources