Ayeshuurr
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Can anyone help me with these questions?

1. compare and explain the enthalpy of hydration of rubidium and strontium
2. explain why is it difficult to predict which lattice enthalpy is more exothermic for Na2O and Rb3N
3. which compound will have more exothermic lattice enthalpy, Cacl2 or CaF2? (4 marks)
4. how will the lattice enthalpies of Na2O, NaF and MgO differ?
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therecovery
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Q1:
The enthalpy of hydration depends on two factors. The magnitude of the charge of the ion and the ionic radius. Greater the magnitude of the charge, greater the hydration enthalpy (directly proportional). However, smaller the ion, the more greater the hydration enthalpy (inversely proportional). Rb is in group 1, which means it has a charge of +1. However, Sr is in group 2, which means it has a charge of +2. When it comes to size, both are in the s block. Therefore, both elements have their outer electrons in the s block but Sr would be slightly more bigger than Rb. Despite the fact that Sr is a bigger than Rb, its very small and Rb has the greater charge compared to Sr). Therefore, Rb would give a greater hydration enthalpy compared to Sr.

Additional info: Enthalpy of hydration is the enthalpy change when 1 mol of a gaseous ions are dissolved in excess solvent to give an infintely dilute solution. Do not confuse it with the enthalpy of solution which is when 1 mol of solid is dissolved in excess solvent to give an infinetly dilute solution. Enthalpy of hydration is for gaseous ions whereas enthalpy of solution is for solids.

2. explain why is it difficult to predict which lattice enthalpy is more exothermic for Na2O and Rb3Nwait so, you want to know which one gives the more exothermic lattice enthalpy or why is it difficult to predict the lattice enthalpy of both? Im confused.

3. which compound will have more exothermic lattice enthalpy, Cacl2 or CaF2? (4 marks)CaF2. Lattice enthalpy depends on the size of the charges present and the sum of the ionic radii. Lattice enthalpy is directly proportional to the magnitude of the charges and inversely proportional to the sum of the ionic radii. In this example, the magnitude of charges does not change because both species have a group 2 metal and group 7 non metal. F2 and Cl2 are both in group 7 where Cl2 is lower than F2. Down, group 7, the size of the ion increases. Therefore, F2 has a smaller ionic radii than Cl2. In addition, F2 has less electrons and therefore has less shells. Hence, the lattice enthalpy of CaF2 will be more exothermic than CaCl2.

4. how will the lattice enthalpies of Na2O, NaF and MgO differ?MgO will have the highest lattice enthalpy, followed by Na2O or NaF. Lattice enthalpy depends on two factors (explained earlier).The only way lattice enthalpy can change in Na2o or NaF is by sum of the ionic radii. F is smaller which would mean Na2O has a more exothermic lattice enthalpy. However, the sum of charges is greater in na2o than naf. the effect of charges is more dominant than sum of ionic radii. Therefore, the order is most likely to be MgO, Na2o and Naf.

The last question is a good once, just check up on exactly which one is the dominant effect. the magnitude of charges or the sum of the ionic radiihope this helps. feel free to tell me if anything is unclear.
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Ayeshuurr
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(Original post by therecovery)
Q1:
The enthalpy of hydration depends on two factors. The magnitude of the charge of the ion and the ionic radius. Greater the magnitude of the charge, greater the hydration enthalpy (directly proportional). However, smaller the ion, the more greater the hydration enthalpy (inversely proportional). Rb is in group 1, which means it has a charge of +1. However, Sr is in group 2, which means it has a charge of +2. When it comes to size, both are in the s block. Therefore, both elements have their outer electrons in the s block but Sr would be slightly more bigger than Rb. Despite the fact that Sr is a bigger than Rb, its very small and Rb has the greater charge compared to Sr). Therefore, Rb would give a greater hydration enthalpy compared to Sr.

Additional info: Enthalpy of hydration is the enthalpy change when 1 mol of a gaseous ions are dissolved in excess solvent to give an infintely dilute solution. Do not confuse it with the enthalpy of solution which is when 1 mol of solid is dissolved in excess solvent to give an infinetly dilute solution. Enthalpy of hydration is for gaseous ions whereas enthalpy of solution is for solids.

2. explain why is it difficult to predict which lattice enthalpy is more exothermic for Na2O and Rb3Nwait so, you want to know which one gives the more exothermic lattice enthalpy or why is it difficult to predict the lattice enthalpy of both? Im confused.

3. which compound will have more exothermic lattice enthalpy, Cacl2 or CaF2? (4 marks)CaF2. Lattice enthalpy depends on the size of the charges present and the sum of the ionic radii. Lattice enthalpy is directly proportional to the magnitude of the charges and inversely proportional to the sum of the ionic radii. In this example, the magnitude of charges does not change because both species have a group 2 metal and group 7 non metal. F2 and Cl2 are both in group 7 where Cl2 is lower than F2. Down, group 7, the size of the ion increases. Therefore, F2 has a smaller ionic radii than Cl2. In addition, F2 has less electrons and therefore has less shells. Hence, the lattice enthalpy of CaF2 will be more exothermic than CaCl2.

4. how will the lattice enthalpies of Na2O, NaF and MgO differ?MgO will have the highest lattice enthalpy, followed by Na2O or NaF. Lattice enthalpy depends on two factors (explained earlier).The only way lattice enthalpy can change in Na2o or NaF is by sum of the ionic radii. F is smaller which would mean Na2O has a more exothermic lattice enthalpy. However, the sum of charges is greater in na2o than naf. the effect of charges is more dominant than sum of ionic radii. Therefore, the order is most likely to be MgO, Na2o and Naf.

The last question is a good once, just check up on exactly which one is the dominant effect. the magnitude of charges or the sum of the ionic radiihope this helps. feel free to tell me if anything is unclear.

Thankyou so much, that really helped and on question 2, it's why is it difficult to predict the lattice enthalpy of both
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therecovery
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Hmm. its the same case like in q4 where we need to decide if Na2o or naf has the greater lattice enthalpy with the whole dominant effect. post your answer for the second one and ill go through it. it will also tell us if you got the concept or not. if you got great, if you didnt, ill help out again. so yeah, fire away

similar idea here:
https://uk.answers.yahoo.com/questio...5070957AAHm9hS
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