Periodic Table II

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thebluhood
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#1
Report Thread starter 11 months ago
#1
Dear all,
I'm having some difficulty with this question. If someone could kindly explain why the answer is B, I would really appreciate it!

P, Q and R are Group 2 elements. They form compounds with the following properties.

P(NO3)2 has a higher thermal decomposition temperature than R(NO3)2 RCO3 has a more endothermic enthalpy change of decomposition than QCO3

Which of the following statements is correct? A) Po has a more exothermic lattice than RO B) QCl2 has more covalent character than PCl2 C) R is more reducing than P D) Q is Mg and R is Ba

Thank you for taking the time to read this. Have a nice day!
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deskochan
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#2
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1. P(NO3)2 has a higher thermal decomposition temperature than R(NO3)2.

That means P(NO3)2 is stronger ionic bonding than R(NO3)2

2. RCO3 has a more endothermic enthalpy change of decomposition than QCO3

That means RCo3 is stronger ionic bonding than QCo3

Summarize strength of ionic bond-forming P>R>Q; the covalent character of ionic bond Q>R>P

Because P, Q, and R are Group 2 elements, they are the same charge and the only size of ion determines the polarising power, and the more polarising power, the more covalent character in the ionic bonding. Hence, the size of the atom Q<R<P and the size of ion Q2+<R2+<P2+.

A) PO has a more exothermic lattice than RO
That means P2+ is smaller than R2+.

B) QCl2 has more covalent character than PCl2

C) R is more reducing than P
On moving down the group, the atomic size increases. The electropositive character increases and the ionization enthalpy value decreases
D) Q is Mg and R is Ba
beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr) and barium (Ba)
It implies R is the largest size.
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KrissKross
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#3
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#3
(Original post by thebluhood)
Dear all,
I'm having some difficulty with this question. If someone could kindly explain why the answer is B, I would really appreciate it!

P, Q and R are Group 2 elements. They form compounds with the following properties.

P(NO3)2 has a higher thermal decomposition temperature than R(NO3)2 RCO3 has a more endothermic enthalpy change of decomposition than QCO3

Which of the following statements is correct? A) Po has a more exothermic lattice than RO B) QCl2 has more covalent character than PCl2 C) R is more reducing than P D) Q is Mg and R is Ba

Thank you for taking the time to read this. Have a nice day!
A. if P has a higher thermal decomposition temperature than R, it must be more reactive. As you go drown group 2, reactivity increases, therefore the larger the atom, the more reactive. This is the opposite for a lattice, as oxygen is a relatively small atom and P would be a relatively large atom, they have a weaker attraction to one another because P is such a big atom therefore R will have a stronger exothermic lattice because it has a stronger attraction to O, making it harder to separate, therefore a higher exothermic lattice so WONG

B. Similar to A, as P is highly reactive, it's more likely to form ionic bonds than covalent bonds, whereas Q is the least reactive and therefore cannot form ions as readily as P, so RIGHT

C. Reduction is to gain electrons or hydrogen and to lose oxygen, as P is more reactive than R, it will most likely have a larger atomic radius making it easier for electrons to be lost. Therefore P is more likely to be reduced itself and R is more likely to reduce something else, another species, rather than P, so WRONG

D. Decomposition is endothermic so the more endothermic it is, the more energy is needed to be put in to break the bonds. Now Ba is lower down group 2 so it's highly reactive, therefore it needs less energy to be put in, making it less endothermic. However, the statement says that it's more endothermic, meaning it is less reactive than Q and needs way more energy put into it for it to decompose compared to Q so WRONG
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