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CL is more electronegative than I so Iodine in KI cannot replace CL from HCL.....Can anyone explain to me why doesn't HCL react with KI to produce chlorine gas?
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CL is more electronegative than I so Iodine in KI cannot replace CL from HCL.....Can anyone explain to me why doesn't HCL react with KI to produce chlorine gas?
No problem! Feel free to ask more via pm or on here.
Please explain..................
Thanks broFor Q32, we know that the first statement is true simply because of the existence of ONA at the end as well as the entire sulphate group. It's used as a detergent too so it makes sense some of it must be soluble, or so I think. 2 is correct because alkyl chains are hydrophobic, so while they don't dissolve in water, they do dissolve in organic solvents like oil droplets. Finally, 3 is correct because as you can see all carbons are attached to 4 other atoms so it must be tetrahedral. All 3 statements are correct. Answer is A.
For Q33 you have to picture the diagram for Hess' law. When you atomize graphite or diamond, you will end up with the same product i.e. gaseous carbon atoms. So, imagine that to get to gaseous carbon atoms, you have two routes, one from graphite directly to gaseous carbon atoms, the other from graphite to diamond and then to gaseous carbon atoms:
Graphite --- > Carbon atoms
Graphite --- > Diamond --- > Carbon atoms
Since graphite to diamond is endothermic, and since atomisation itself is also always endothermic, this means that when going from graphite to diamond, some of the energy needed to go from graphite to carbon is already added, and then the rest is used to go from diamond to carbon. In other words, according to Hess' law, if you start with graphite and end with carbon atoms, then the total energy must be the same, let's call it X. Let's call diamond to carbon atoms Y, and graphite to diamond is given as 3.
Graphite -- > Carbon atoms = X kJ/mol
Graphite --- > Diamond = +3 kJ/mol --- > Carbon atoms = Y kJ/mol
X kJ/mol = +3 + Y kJ/mol
Thus, X kJ/mol is greater than Y kJ/mol, i.e. graphite's direct atomisation is greater than diamond's atomisation. This makes the first statement correct.
For the second statement, again, it's another version of atomisation. Since we need to add MORE energy to break bonds in graphite compared to diamond, this means that the bond enthalpy of graphite IS greater than the bond enthalpy of diamond.
For the third statement, we know that combusion is always exothermic, and you have to imagine another Hess' law diagram in your mind. The end product for the combustion of either graphite or diamond is CO2, and the enthalpy change is negative. Thus,
Graphite --- > CO2 = -A kJ/mol
Graphite --- > Diamond = +3 kJ/mol --- > CO2 = -B kJ/mol
-A kJ/mol = +3 - B kJ/mol
Thus, since the MAGNITUDE of the CHANGE is being referred, you can multiply the equation by -1 to consider the magnitudes. This turns it into:
A kJ/mol = -3 + B kJ/mol
SInce you have to subtract from B to get A, this means B as a CHANGE of enthalpy in MAGNITUDE is greater than A, making the third statement correct too. If they asked which one of the two is MORE negative or LESSER in VALUE, then it would ALSO be B, but that means that the CHANGE in enthalpy of B is GREATER than A. Don't let the signs confuse you and make sure you understand this perfectly. All 3 statements are correct. Answer is A.
For question 14, I don't think you need to thinkt too hard about it. Overthinking can cause problems too. In reaction 1 all we're doing is DECOMPOSING a compound, so that means you ADDED heat to BREAK it down, which means it's endothermic. In reaction 2, in all honesty this is where I say that the book recommended by CIE is HIGHLY HIGHLY valuable. I wish I knew about it in my A Level, I wouldn't have bothered going to class. Reaction 2 is described WORD for WORD in the Cambridge book, it says:
Calcium oxide, CaO, reacts with water to form calcium hydroxide. If water is dripped onto the surface of a lump of calcium oxide it causes a vigorous reaction. It gives off so much heat that some of the water boils off as the solid lump appears to expand and cracks open.
As you can see, it gives off heat and is exothermic. Even the reaction 1 is described as:
The carbonates and nitrates of the Group 2 elements decompose when heated.
Thus, reaction 1 is endothermic, 2 is exothermic. And the quotations are taken from pages 166 and 168 of Cambridge International AS and A Level Chemistry Coursebook Second Edition by Lawrie Ryan and Roger Norris. Get this book, I can gaurantee you no question will come from outside of it. As much as we A Level kids tend to assume that FSc kids only get book questions, and although the majority of A Level questions ARE conceptual, but that little difference that'll get you the A* is only made up by learning from the book directly too.
Bro, help..........For Q32, we know that the first statement is true simply because of the existence of ONA at the end as well as the entire sulphate group. It's used as a detergent too so it makes sense some of it must be soluble, or so I think. 2 is correct because alkyl chains are hydrophobic, so while they don't dissolve in water, they do dissolve in organic solvents like oil droplets. Finally, 3 is correct because as you can see all carbons are attached to 4 other atoms so it must be tetrahedral. All 3 statements are correct. Answer is A.
For Q33 you have to picture the diagram for Hess' law. When you atomize graphite or diamond, you will end up with the same product i.e. gaseous carbon atoms. So, imagine that to get to gaseous carbon atoms, you have two routes, one from graphite directly to gaseous carbon atoms, the other from graphite to diamond and then to gaseous carbon atoms:
Graphite --- > Carbon atoms
Graphite --- > Diamond --- > Carbon atoms
Since graphite to diamond is endothermic, and since atomisation itself is also always endothermic, this means that when going from graphite to diamond, some of the energy needed to go from graphite to carbon is already added, and then the rest is used to go from diamond to carbon. In other words, according to Hess' law, if you start with graphite and end with carbon atoms, then the total energy must be the same, let's call it X. Let's call diamond to carbon atoms Y, and graphite to diamond is given as 3.
Graphite -- > Carbon atoms = X kJ/mol
Graphite --- > Diamond = +3 kJ/mol --- > Carbon atoms = Y kJ/mol
X kJ/mol = +3 + Y kJ/mol
Thus, X kJ/mol is greater than Y kJ/mol, i.e. graphite's direct atomisation is greater than diamond's atomisation. This makes the first statement correct.
For the second statement, again, it's another version of atomisation. Since we need to add MORE energy to break bonds in graphite compared to diamond, this means that the bond enthalpy of graphite IS greater than the bond enthalpy of diamond.
For the third statement, we know that combusion is always exothermic, and you have to imagine another Hess' law diagram in your mind. The end product for the combustion of either graphite or diamond is CO2, and the enthalpy change is negative. Thus,
Graphite --- > CO2 = -A kJ/mol
Graphite --- > Diamond = +3 kJ/mol --- > CO2 = -B kJ/mol
-A kJ/mol = +3 - B kJ/mol
Thus, since the MAGNITUDE of the CHANGE is being referred, you can multiply the equation by -1 to consider the magnitudes. This turns it into:
A kJ/mol = -3 + B kJ/mol
SInce you have to subtract from B to get A, this means B as a CHANGE of enthalpy in MAGNITUDE is greater than A, making the third statement correct too. If they asked which one of the two is MORE negative or LESSER in VALUE, then it would ALSO be B, but that means that the CHANGE in enthalpy of B is GREATER than A. Don't let the signs confuse you and make sure you understand this perfectly. All 3 statements are correct. Answer is A.
For question 14, I don't think you need to thinkt too hard about it. Overthinking can cause problems too. In reaction 1 all we're doing is DECOMPOSING a compound, so that means you ADDED heat to BREAK it down, which means it's endothermic. In reaction 2, in all honesty this is where I say that the book recommended by CIE is HIGHLY HIGHLY valuable. I wish I knew about it in my A Level, I wouldn't have bothered going to class. Reaction 2 is described WORD for WORD in the Cambridge book, it says:
Calcium oxide, CaO, reacts with water to form calcium hydroxide. If water is dripped onto the surface of a lump of calcium oxide it causes a vigorous reaction. It gives off so much heat that some of the water boils off as the solid lump appears to expand and cracks open.
As you can see, it gives off heat and is exothermic. Even the reaction 1 is described as:
The carbonates and nitrates of the Group 2 elements decompose when heated.
Thus, reaction 1 is endothermic, 2 is exothermic. And the quotations are taken from pages 166 and 168 of Cambridge International AS and A Level Chemistry Coursebook Second Edition by Lawrie Ryan and Roger Norris. Get this book, I can gaurantee you no question will come from outside of it. As much as we A Level kids tend to assume that FSc kids only get book questions, and although the majority of A Level questions ARE conceptual, but that little difference that'll get you the A* is only made up by learning from the book directly too.
Please explain these two
Bro, help..........
few more questions...
It's correct! Thanks a lot bro!I hope I helped and I didn't tally my answer with the mark schemes so let me know if I'm wrong about anyone.
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