J2026 A LEVEL CHEMISTRY SECTION A

[00:00:00]All right, it's Niyaki. It's a Niaki osteo zone. And today we are simply going to revise the June 2026 A level chemistry from the Zimsec exam board as you can see on the screen. Right. So simply going to dissect this paper step by step. And if you are doing Zimse, you need to pay attention to these instructions the candidates and always remember always remember to subscribe so that you'll be notified whenever whenever we post. So we're providing massive revisions in all the sciences.

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[00:00:27]So we got to covered in all the sciences in all the science right. So we starting with section A. So section A is the physical chemistry section and we are required to answer to of two questions but for the sake of revisions we're simply going to answer all the questions in section in section A. So number one says define what is meant by the term bond energy. So bond energy simply defined as the minimum amount of energy required to break one more of a coalent bond in the gaseous in the gas phase. So it's one more of a coalent of a covealent bond in the gasous in the gasous phase. So you should take note of these [music] of these terms highlighted in blue. Right? So it's one more of a of a coalent bond only in the gas phase. So we're dealing with coalent molecules in the gas in the gaseous phase. Right? So you should know the definition of bond energy inside out. Are we together? And then we now proceed at the next part. So let me clear so that you can hear the next part more clear. So the next part says ammonia reacts with oxygen according to this equation. So we're having the oxidation of ammonia to give this nitric oxide in water. Right? So here we are having water in the liquid in the liquid form right and then all these ones are in the gasous in the gasous phase right so this one is the same equation we are simply going to have in the what in the what process we are simply going to have the catalytic oxidation of ammonia in the production of nitric of nitric acid right so you should I believe you guys are all aware of this equation from your old level chemistry right and then the first part says calculate the enthaly change of the reaction given that [music] the bond energy the bond energy of nitrogen to oxygen double bond is equal to 6 or 8 So from the definition we said we're simply going to make use of bond energies when we are only dealing with coalent bonds in the gas in the gas phase but here on this question we're having water in the liquid in the liquid phase right that's where the war confusion is right so whenever you're dealing with these kind of questions and the question is not explicit whether you're supposed to convert this one into the gases phase for you to calculate to proceed the calculation using the bond energy you're simply going to calculate [music] by assuming that this one is in gasous in the gases phase right so that's the only way out on this kind of question. Right?

[00:02:26]So here we're simply going to proceed by calculating water using the bond energy because we're not given the enthaly change of vaporization. Right? We are not given the end of change of vaporization whereby we're simply going to convert this liquid into into the gaseous phase. Right? So we're simply going to proceed by calculating using this one. Right? So always take note on on that one. Right? So whenever in the examination you are given the enthalpy change in the liquid and then you're not given the vaporization. You're simply going to proceed calculating using that one. The bond energies are all together.

[00:02:53]So here we're simply going to have ammonia and then we're having oxygen on this side and then on this side we're having nitric oxide. So here on this side we're having we're having water. So we're simply going straight to the formula. So let me insert another page.

[00:03:05]Let me insert another another page.

[00:03:06]Right? So here the formula of calculating the enthal change using the bond energies. We're simply going to have the enthaly change being equal to the summation of all the bond energies being broken. Right? So the bond energy being broken. So here we're having the bond energies being broken minus the summation of all the bond energies being formed. Right? So here we're having bond energy being formed. So the simple way to memorize this one is reactants minus the products. Are you together? So it's reactants minus the products. Right? So here on the let me write the equation.

[00:03:34]So it's ammonia. So we are having ammonia here plus oxygen to give nitric oxide plus water. And then to balance we need to have a four. [music] It's 4 5 4 6. Right? So here is four. So this one is 4 5 4 6. [music] Right? These are the this one is the equation. Right? So we're simply going to make use of this equation. So we're starting by calculating the bonds are broken. So we're having ammonia. So here this one geometry of ammonia. So here we're having ammonia and then the lone pair to give a trigonal pyramid of angle 107 right from the shapes right. So here we're having one 1 2 3. So we're having three nitrogen to hydrogen bonds. Right?

[00:04:14]So here we're having three in each ammonium ammonium molecule and then here we have used four. So we're simply going to multiply this one by by four. Right?

[00:04:21]So we're simply going to have the bond energy of of nitrogen to [music] hydrogen bond multiplied by by 12.

[00:04:27]Right? So here 3x 4 is 12. So here the resultant one is 12 by N2 H bond right and then we simply going to have oxygen on this side again. So it's oxygen to oxygen double bond oxygen to oxygen double bond. [music] Right? And then we multiply by by five. Right? So here we're simply going to F5 by oxygen to oxygen double bond. Right? So this one on the react sides are the bonds which are simply going to be to be broken.

[00:04:51]Right? So we're simply going straight to the double. We're going straight to the data the double. Right? So that one of nitrogen hydrogen bond is equal to 12 by 390. And then we go on to have that one of oxygen by oxygen to oxygen double bond. So oxygen to oxygen double bond is 496. So it's 496 by by 5. Right? So these are the bones broken all together.

[00:05:13]So we're simply going to calculate the bones broken. So we're having we're having 390 multiplied by 390 * 12. Then we're going to have 46. So it's 46 80 and then you're going to have 5 96 496 m* 5 and then we're going to have 2 48 right and we're simply going to add these two. [music] So this one 46 80 and then we're simply going to have 71 C. So this one is the summation of all the bonds are broken. Right? So here on the bonds broken we're simply going to have 71. Now we are calculating the bonds being formed. Right? So we're having nitric nitric oxide. So nitric oxide we're given that the bond energy is 608 right? So [music] it's 608 this one. So we're simply going to have 4* 68. And then in terms of water, we're still going to have this one, the bench shape of water, this one, two lone pairs here, and then the bonding of 104. So we're still going to have this two oxygen two hydrogen bonds, right? So here we're having two for every molecule, right? So it's two [music] oxygen to hydrogen bonds. And then we're simply going to have six here, right? So we're simply going to multiply this one also by two by six again, right? To give us 12 oxygen to hydrogen bonds are together.

[00:06:29]So here in terms of from the double the oxygen to hydrogen bond the single bond we're simply going to have to four right so it's 12 by 4 by 4 together so we're simply going to multiply 12 * 4 and then we're simply going to have 55 20 right so it's 55 20 and then here is four this one is 608 * 4 and then simply going to add with this one 55 so this one + 55 And then we're simply going to have this one being go to 7952. So here we're having 79 50 52 all together. So here this one the bonds which are simply going to be formed and then here the bonds which are simply going to be to be broken all together. So we're simply going to subtract this one and this one right like we have alluded to before.

[00:07:16]Are we together? So we're simply going to have 716 minus 79 52. Are we together? And then we're still going to have so let me clear here so that we can have uh we can have the sign we can have the the enthaly change more clear right so here we're having the enthaly change being equal to 72 9 kiloj right so here in terms of enthaly change of the reaction it is the energy change when reactants reacts to give product according to the number the stochometrical number of moles in the in the equation right so here we're simply going to have that one is the end of change of the of the reaction together and we are and we are done and then we now move on to the part which requires us to draw the energy profile. So here we're having this negative this negative sign indicating that the reaction is moving in the exothermicity in the exothermicity direction. So simply going to draw that one of an exothermic reaction right. So here in terms of the energy profiles you need to know that this one in terms of the exothermic reaction we're simply going to have the energy being lost to the surroundings meaning to say the products are at lower energy compared to the reactants. So here having the products here we're having the reactants. This one is for the exothermic reaction. And then in terms of the endothermic reaction, we simply going to have the heat being absorbed.

[00:08:27]So we're simply going to have the products at a higher energy level compared to the to the reactants. So here we're having the the products, here we're having the reactants and this one is for the endothermic reaction. So if the reaction is moving in the endicity direction, we simply going to have this one as the energy profile and then in the exothermicity direction, we are simply going to have this one as the energy profile. Are we together? So here we are having this one moving in this is the direction indicated by this negative sign. Are we together? So we're simply going to draw the one for the reaction.

[00:08:55]So let me draw here the clear one. So we're having the reactance at a high energy level compared to the compared to the products. Right? So here we're having the the products and then here we're having the energy right? So here's energy and then here we are simply going to have the progression of the reaction.

[00:09:11]So here we're having the progression of the reaction. So here we're simply going to have this one from this point going to this point is the activation activation energy defined as the minimum amount of energy required to start a chemical reaction. So if the arrow is pointing upward you simply mean to say it is an endothermic reaction. So from the bone up cycle you must know the direction of the arrow pointing upwards endothermic pointing downward exothermic from the bone up cycle right and then here we're simply going to have this one uh let me highlight this one. [music] So here we're having this reaction as an exothermic reaction right? So simply going to have the arrow pointing downwards, right? So this one is the enthalpy enthalpy change, right?

[00:09:48]Pointing downwards because the reaction is an exothermic reaction and then you're simply going to have them the reactants. So for the reactants, we're having ammonia here plus oxygen here, right? Plus oxygen. And then in terms of the products, we're simply going to have the nitric oxide plus water, right? Here these are the these are the um the products, right? And then we're simply going to have this topometrical ratio.

[00:10:08]So it's 45 46, right? So it's simply going to have four here and then a five there and then here four and then a six there. The reaction is now is now balanced and we are and we are done. So this one is the energy profile of for the reaction, right? Are we together?

[00:10:22]And then in terms of an endothermic reaction here, the endothermic reaction.

[00:10:26]We simply going to have this one is the energy change, right? This one is the enthropy change and then this one from here going to there it is the activation activation energy and then this one is the activation energy and then this one is the end of change for an exothermic exothermic reaction. So you must know these energy profiles [music] by heart. You must know these ones by by heart. Are you together? And then now let us go to the next part of the question. The next part says explain the relationship between the bond length and the bond energy in a covealent in a coalent bond. Right? So we are required to give the relationship, right? The relationship connecting bond length and bond and bond energy, right? So if we are to have a shorter bond length, we're still going to have a stronger bond and then we're still going to have a higher bond bond energy, right? So why? So here we're simply going to have this one. Let us take for example in group seven. So in group seven, we're simply going to start with florine and then we go to chlorine and then we're simply going to go to bromine. Right? So here and then we go to iodine. So let us ignore florine because it has got an anomaly.

[00:11:23]We starting with chlorine. So I simply going to explain they normally for florine later but for now let us go for for chlorine. So we having this one is a chlorine right? So this one the bond joining chlorine atoms two chlorine atoms right we have a single bond joining these two and then we go to iodine. So this one is the iodine right a larger so let me create a larger atomic atomic size right. So this one is the iodine [music] and then here we're having this one and then this one right.

[00:11:45]So here as you can see the bond the bond length is is a long bond and then this one is a shorter shorter bond. Right? So we are simply going to have poor orbital overlap here. So it's poor orital overlay between these two iodine atoms.

[00:11:56]And then here we're simply going to have effective orbital overlay between these two chlorine chlorine atoms. So we're simply going to have the bond shorter because of the effective orbital overlap in this shorter bond. Right? Compared to this one, a longer bond, right? So the relationship here between the bond length and the bond energy, you're simply going to have shorter bonds having a stronger or a higher bond energy. And then the opposite is true.

[00:12:17]We're simply going to have a lower we're simply going to have longer longer bonds being [music] being weaker because of the poor orbital overlap which result in poor attraction between the positive nucleus and the sea of deogized electrons. Right? So we're simply going to have this positive nucleus and then here we're having a coalent bond meaning to say we're simply going to have the sharing of electrons. So we're simply going to have the electron cloud the electron density being being here. So we're simply going to have this [music] the nuclear charge here attracting this these electrons here the electron cloud right. So here the forces are simply going to be to be weaker compared to here the distance from this positive nuclear charge to this one is shorter meaning to say the stronger the attraction right right and we are and we are done so we said we simply going to explain the issue of florine right so this one it is from inorganic but we simply going to highlight here so here we're having florine right so florine it is very very small in group seven allergens so we're having florine is very very small and then it has three lone [music] pairs here right we're having three lone pairs here right so the loan pairs are being clustered in a small region. Meaning to say we're simply going to have electrons from this atom and then electrons on this atom being clustered in a small region.

[00:13:19][music] Meaning to say we're simply going to have negative cloud here and then negative electron cloud there. So from the basics we know that like charges are simply going to repel each other. Then unlike charges are simply going to attract. So here we're having like negative charges. [music] This one is negative. This one is negative. So we're simply going to have like negative charges. So we're simply going to have repulsive forces. So that's why we are having a shorter bond length in florine. But the bondage is very very low because of the repulsive forces, right? Because of these repulsive repulsive forces. Are we together? So we must take note of of florine. So we said longer bonds are weaker and then shorter bonds are stronger except for of florine. We have the anomaly of florine. Though it is a shorter bond bond length, we still going to have the bond energy being weaker together. So we have explained with respect to for florine, right? And then we go on to the next to the next part.

[00:14:09]We are now moving on to the next part where we are simply going to be given carbon monoxide reacting with hydrogen to produce methanol and then we are required to write the equation or the reaction right. So we simply going to have carbon monoxide plus hydrogen and then we simply going to have the formation of of this one or methanol and then to balance this equation we simply need to have [music] we need to have a two here and that the equation is now balanced right and we are done and then we go to the next part. So the next part says table 1.1 shows the standard enthaly changes of combustion of carbon monoxide [music] hydrogen and methanol right so we're given standard enthaly change of combustion right so standard end of change of combustion is the heat evolved it is always the heat evolved meaning to say it is always exothermic right heat evolved meaning to say it is always exothermic so it is the heat evolved when one more substance is completely bent in excess oxygen right in excess oxygen under the standard conditions of 18 atm into 298 Kelvin right so these ones you must know the standard conditions by heart right so whenever we are very sure that all the the enthal changes are exothermic that's why we only say it is the heat evolved right for example latis energy hydration combustion these are the only ones we are very sure that all these enth changes are exothermic but if we to have enth of solution enthchange of formation we are not sure at times it can be exothermic at times it can be endo endothermic so we are not going to say it is the heat evolved. We are only going to say it is [music] the heat the heat change because we are not sure because at times it can be endothermic at times it [music] can be exothermic.

[00:15:41]But if you also to have atomization activation energy ionization and all the electron affinities except the first [music] one except the first one. So all the electron affinities are endothermic except the first electron affinity which is exothermic. So we are simply going to highlight that one. Right? So here we're having atomization activation energy ionization and all the electron affinities are endothermic. So we are saying we define them with respect to the heat being absorbed. So it is the heat being absorbed right and then here the heat evolved the heat absorbed and then the heat change when we are not sure. So why is the first why is the first electron affinity exothermic right? So let us highlight this one. So here we don't mainly focus on claiming papers highlighting to the given questions but we try to broad our foundation in any of the concept within the given radius. Right? So that you can have the full understanding you can comprehend all the concept using this only one video. Right? So here we are given the electron affinity for having this nuclear charge and then electron affinity is defined as the energy change when one more of a gaseous atom absorbs one more one more of electrons to form one more of a gaseous uni negative ion.

[00:16:46]So here here we having this electron and then want to have this electron being absorbed by this atom. Right? So here we have this nucleus which is positively charged and then we're having this electron. So simply going to have attraction between these two and then direction is highly favored and then we're simply going to have it as an exothermic. But here from there going onwards we simply going to adding electrons to to an already negative ion.

[00:17:07]Right? So this one is negatively charged. It has [music] it has gained an electron from this first reaction. So we simply going to add an electron to the first one. So here by having this nuclear charge attracting this one and we also having this electron repelling this incoming electron. So we're simply going to have mutual repulsions. You're still going to have inter electronic repulsions between these the negatively charged ion and the incoming electron.

[00:17:26]So you're simply going to force this electron into this onto this. So you're simply going to use energy energy is being absorbed energy is being employed to facilitate this reaction. That's why it is that's why all the electron affinities are said to be endothermic in nature from the second one going onwards. Right? So you must understand why the first one is exothermic and then this one all these ones are endothermic because it is highly it is frequently examined in your examinations. Are we together? So let us proceed at the given the given question right. So let me clear here so that we can have the given question more clear right. So here we are one we are required to calculate the standard end of change we're given the end of change of combustions of carbon monoxide this one hydrogen this one methanol this one right. So we required to calculate the energy the end change of the reaction. So we having this equation. So we simply going to make use of what you call the yes law. So the law state said that the end of change of reaction is independent to the to the root taken provided that all the conditions are kept constant. Right? So here we're having carbon monoxide and combustion to give carbon dioxide and then here we're simply going to have water. So these are the common products.

[00:18:28]So here we're simply going to have these two. Combustion of methan will give us these ones. Hydrogen will also give us these ones and then this one also give us this one. And then here we're having this one. Let me clear here right so that we can have the full question more clear. So here it's hydrogen 2. So here this one is the root one and then here we're having this one is our root2.

[00:18:49]So we said the root the end of change is the same provided that all the conditions are kept constant. So root one is equal to roo<unk>2. So you want the end of change of the reaction which is root one. So here in root two we're still going to have the combustion of carbon monoxide which is minus 283 and then that one of hydrogen is minus 286 and then we're having two. So simply going to multiply this one by two and then that one of methanol we're having it as minus 1 - 71 5 right and then in terms of methano as you can see the arrow is going in this direction and then for methan it is going in this direction going to change the direction right so if we to change the direction we're simply going to change the sign and then the magnitude remains constant so here it's minus so if we to change the sign it is going to be plus 7 + 7 1 5 right so this one we're simply going to [music] add this one so Here is R1 is equal to R2 which is this one - 283 [music] and then we're simply going to add this one which is - 286 by -2. So it's minus it's 2 by - 2 8 6 and then simply going to add + 75 right and then we simply going straight at the calculator right so here we are simply going to the calculator so it's 2 * 2 86 and then we simply going to have - 283 - 572 + [music] 71 5 being equal to r 1 and then here we still going to have minus + 2 [music] 8 3 - 5 72 and then we simply going to have this one and then we add 715 then we simply going to have R1 being equal to minus 140 kilogj and we are and we are done right and then we now proceed the next part let us proceed the next the next part right so the next part says a mass of 5 g of salt so this one it is the hydrated aluminium and then we're simply going to have this sort of crystallization. So water of crystallization is defined as the amount of amount of water bonded to one more of the salt in the latice structure. So it is bonded to one more of the salt.

[00:20:55]That's the definition of water of crystallization. Right? So this one was heated until we simply going to have a constant mass of 3.2 g. So here going to have the anra salt because we have heated it all the water has been removed. Right? So simply going to have this one is the mass of the salt. So here this one is the mass of the hydrated salt. This one is the mass of the anra salt. So we want to calculate the mass of the water. So mass of the water is equal to mass of the hydrated salt and the mass of the salt which is equal to 5 - 3.2 right? So we're simply going to have the mass of water being equal to 5 - 3.2 and then we're going to have 1 1.8 g as the mass of the of the water and then we're simply going to calculate the number of moles of water.

[00:21:35]So n of water is equal to mass over m and then we are going to have mass being 1.8 over the m being= to 18. So this one divided by 18 and then we're going to have the number of moles of water being equal to 0.1 moles of of water. So these are the number of moles of water. And then here we want to calculate the number of moles of the aluminium aluminium sulfate salt. Right? So we're simply going to use the same achieve equation. Right? So we're simply going to have n again being to mass over mr. Then we're going to have our mass being equal to 3.2 and then our m of the salt.

[00:22:08]So here we're having the aluminium being equal to 27 how many aluminum atoms we having two so by two and then the of sulfur being equal to 32 sulf we having by three and then oxygen 16 how many oxygen are we having by 12 right and then we're simply going to add these three [music] ars right so here 27 27 m* 2 we're simply going to have 54 and then 32 by 3 so it's 32 m* 3 we're going to have 96 and then here 16 16 * 12 we going so it's 16 * 12 we going to have 192 192 and simply [music] going to add these three so it's 192 + 96 + 54 and then we're simply going to have 342 so here is 3 42 so the number of moles we simply going to have 3.2 2 / 3 42 and then we're simply going to have the number of moles being equal to 0 93 56 725. So these are the number of moles of of the salt which is aluminium sulfate.

[00:23:15]Right? So here we have defined the water of crystallization as the amount of moles of water bonded to one mole of the salt. So we are having one mole of the salt. So here we're having this amount of the salt bonded to the amount the number of moles of water we having this one bonded to 0.1. So how many moles of water simply going to be bonded to one more of the salt we simply going to have more right? So here we having 1 / 0.93 567 and then we're simply going to have 0.0.1 right? So we're simply going straight as the calculator and then we're simply going to have let's store this one is a. So we're simply going to store is a. So we're having 1 / alpha a and then we are simply going to multiply with 0.0.1 and then we're simply going to have 10.6875 [music] and then to round to the nearest whole number we're simply going to have this one above five. So we're simply going to have 11 this one right. So the value of n is equal to is equal to 11. How you get? So we're simply going to have n the value of n being equal to 11. And we are and we are done. So always remember always remember to subscribe so that you'll be notified whenever whenever we post. So we're now moving on to number number two. All right. So this one is our Niaki online tutotoring as you can see on the screen. So we specialize in sciences. We specialize in sciences. So we have pyramids, chemistry, physics, biology, combined science, mechanics and [music] statistics for both the O levels and the A levels. Right? So we have our standard package, we have our premium package. We have our premium pro max package. Right? So these are affordable.

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