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Chemistry unit 4 revision quiz TONIGHT AND UNTIL NEXT THURSDAY!
I'll be doing revision quizzes every week. I'll post the questions and people can p.m. me with their answers this week and i'll give you a score. The winner will get rep. Good luck!
Whether you're doing unit 4 in jan revision or studying for synoptic, try not to cheat!
Topic today is energetics.
1) Define the term lattice energy. (3 marks)
2) Define the term enthalpy of atomisation (2 marks)
3) Define the term enthalpy of hydration (3 marks)
4) Construct an ionic equation to show the lattice energy of an ionic solid MX where M is a cation and X is an anion with charges of +1 and -1 respectively. (2 marks)
5) Why do lattice energy values differ for some compounds when calculated using the Born-Haber cycle and a purely ionic model? (2 marks)
6) State two factors which affect the lattice energy of an ionic solid. (2 marks)
7) Why is lattice energy and hydration energy exothermic? (1 mark)
8) Express enthalpy of solution in terms of lattice energy and the hydration enthalpies of the ions. (2 marks)
9) Explain in terms of the hydration enthalpy of ions and lattice energy and your answer to 8) why the solubility of hydroxides increases down the group and why the solubility of sulphates decreases down the group. (6 marks)
10) Would you expect enthalpy of atomisation of potassium to be more or less endothermic than lithium. Why? (2 marks)
Total = 25 marks.
I'll post marks by next Thursday. Thanks!
Widowmaker.
Whether you're doing unit 4 in jan revision or studying for synoptic, try not to cheat!
Topic today is energetics.
1) Define the term lattice energy. (3 marks)
2) Define the term enthalpy of atomisation (2 marks)
3) Define the term enthalpy of hydration (3 marks)
4) Construct an ionic equation to show the lattice energy of an ionic solid MX where M is a cation and X is an anion with charges of +1 and -1 respectively. (2 marks)
5) Why do lattice energy values differ for some compounds when calculated using the Born-Haber cycle and a purely ionic model? (2 marks)
6) State two factors which affect the lattice energy of an ionic solid. (2 marks)
7) Why is lattice energy and hydration energy exothermic? (1 mark)
8) Express enthalpy of solution in terms of lattice energy and the hydration enthalpies of the ions. (2 marks)
9) Explain in terms of the hydration enthalpy of ions and lattice energy and your answer to 8) why the solubility of hydroxides increases down the group and why the solubility of sulphates decreases down the group. (6 marks)
10) Would you expect enthalpy of atomisation of potassium to be more or less endothermic than lithium. Why? (2 marks)
Total = 25 marks.
I'll post marks by next Thursday. Thanks!
Widowmaker.
hey widowmaker, hope you don't mind me advertising on your thread , but there's going to be a comp at 8pm on my thread: http://www.thestudentroom.co.uk/showthread.php?t=186158&page=5Sorry for taking your customers but it will only take 10mins max, the organic reaction comp will be released at 8pm (in 43mins).
, but there's going to be a comp at 8pm on my thread: http://www.thestudentroom.co.uk/showthread.php?t=186158&page=5Sorry for taking your customers but it will only take 10mins max, the organic reaction comp will be released at 8pm (in 43mins).
Widowmaker
I'll be doing revision quizzes every week. I'll post the questions and people can p.m. me with their answers this week and i'll give you a score. The winner will get rep. Good luck!
Whether you're doing unit 4 in jan revision or studying for synoptic, try not to cheat!
Topic today is energetics.
1) Define the term lattice energy. (3 marks)
2) Define the term enthalpy of atomisation (2 marks)
3) Define the term enthalpy of hydration (3 marks)
4) Construct an ionic equation to show the lattice energy of an ionic solid MX where M is a cation and X is an anion with charges of +1 and -1 respectively. (2 marks)
5) Why do lattice energy values differ for some compounds when calculated using the Born-Haber cycle and a purely ionic model? (2 marks)
6) State two factors which affect the lattice energy of an ionic solid. (2 marks)
7) Why is lattice energy and hydration energy exothermic? (1 mark)
8) Express enthalpy of solution in terms of lattice energy and the hydration enthalpies of the ions. (2 marks)
9) Explain in terms of the hydration enthalpy of ions and lattice energy and your answer to 8) why the solubility of hydroxides increases down the group and why the solubility of sulphates decreases down the group. (6 marks)
10) Would you expect enthalpy of atomisation of potassium to be more or less endothermic than lithium. Why? (2 marks)
Total = 25 marks.
I'll post marks by next Thursday. Thanks!
Widowmaker.
Whether you're doing unit 4 in jan revision or studying for synoptic, try not to cheat!
Topic today is energetics.
1) Define the term lattice energy. (3 marks)
2) Define the term enthalpy of atomisation (2 marks)
3) Define the term enthalpy of hydration (3 marks)
4) Construct an ionic equation to show the lattice energy of an ionic solid MX where M is a cation and X is an anion with charges of +1 and -1 respectively. (2 marks)
5) Why do lattice energy values differ for some compounds when calculated using the Born-Haber cycle and a purely ionic model? (2 marks)
6) State two factors which affect the lattice energy of an ionic solid. (2 marks)
7) Why is lattice energy and hydration energy exothermic? (1 mark)
8) Express enthalpy of solution in terms of lattice energy and the hydration enthalpies of the ions. (2 marks)
9) Explain in terms of the hydration enthalpy of ions and lattice energy and your answer to 8) why the solubility of hydroxides increases down the group and why the solubility of sulphates decreases down the group. (6 marks)
10) Would you expect enthalpy of atomisation of potassium to be more or less endothermic than lithium. Why? (2 marks)
Total = 25 marks.
I'll post marks by next Thursday. Thanks!
Widowmaker.
Are you sure those questions are module foure? which board please.
it's edexcel unit 4
Manifest
Are you sure those questions are module foure? which board please.
edexcel.
Hmmm...I'll try to answer them tomorrow.It's getting pretty late now.
Well I can't really expect anyone else to participate so I'll post the results.
Spoiler
dammit, she beat me!!!! NOOOOOO!!!!!!!
ARGH!!!!!!
could you tell me the questions I got wrong? (PM me- prevents the embarassment)
ARGH!!!!!!
could you tell me the questions I got wrong? (PM me- prevents the embarassment)
you put my user name first, does that mean 1st place?
Noway! I guessed a 2 or 3 of them!
Mwahaha......hehe
dammit, she beat me!!!! NOOOOOO!!!!!!!
ARGH!!!!!!
ARGH!!!!!!
Mwahaha......hehe
mizfizzy815's answers
1) Define the term lattice energy. (3 marks)
Energy released when 1 mole of an ionic compound is formed from its separate gaseous ions under standard conditions (298K and 1atm). It is always exothermic. Eg. Na+(g) + Cl-(g) --> NaCl(s).
2) Define the term enthalpy of atomisation (2 marks)
The energy required to produce 1 mole of gaseous atoms from its elements in their standard states. Eg. ½ Cl2(g) --> Cl(g)
3) Define the term enthalpy of hydration (3 marks)
The energy released when 1 mole of gaseous ions is mixed with excess H2O to form dilute solution, until no more heat is evolved. Na+(g) + aq --> Na+(aq)
4) Construct an ionic equation to show the lattice energy of an ionic solid MX where M is a cation and X is an anion with charges of +1 and -1 respectively. (2 marks)
M+ (g) +X-(g) --> MX(s)
5) Why do lattice energy values differ for some compounds when calculated using the Born-Haber cycle and a purely ionic model? (2 marks)
This happens when the bond is partially covalent. The value of the lattice energy from the Born-Haber cycle will be greater than that from the purely ionic model. This usually occurs when the cation is very polarising or the anion very polarisable.
6) State two factors which affect the lattice energy of an ionic solid. (2 marks)
- Value of the charges
- Sum of radii of ions
7) Why is lattice energy and hydration energy exothermic? (1 mark)
This is due to the forces of attraction between the negative and positive ions. ???
[B]8) Express enthalpy of solution in terms of lattice energy and the hydration enthalpies of the ions. (2 marks)[/B]∆ Hsoln = -(lattice energy) + (hydration enthalpy of each cation + hydration enthalpy of each anion. )
9) Explain in terms of the hydration enthalpy of ions and lattice energy and your answer to 8) why the solubility of hydroxides increases down the group and why the solubility of sulphates decreases down the group. (6 marks)
As the cations size increases down the group, the enthalpy of hydration decreases. This is because the ionic radius increases down the group while the charge remains the same. Furthermore, because the radius of the hydroxide is similar to that of the cations, any increase in the size of the radius causes a considerable decrease in the value of the lattice energy. With reference to the above equation and the factors mentioned; the enthalpy of solution becomes considerably more exothermic as you go down the group.
As you go down the group, the solubility of the sulphates decreases. This is because the enthalpy of hydration decreases as the cations becomes bigger. Also, because the radius of the sulphate ion is much larger than the radius of any of the group 2 cations, the lattice energy only decreases slightly. Both these factors, cause the enthalpy of solution to become considerable less exothermic; thus decreasing the solubility of the group 2 ions down the group.
10) Would you expect enthalpy of atomisation of potassium to be more or less endothermic than lithium. Why? (2 marks)
Less endothermic because as you go down the group the size of the atom increases causing it to be easier to convert one mole of the atom in their standard state to one mole of the atom in the gas phase. ????
1) Define the term lattice energy. (3 marks)
Energy released when 1 mole of an ionic compound is formed from its separate gaseous ions under standard conditions (298K and 1atm). It is always exothermic. Eg. Na+(g) + Cl-(g) --> NaCl(s).
2) Define the term enthalpy of atomisation (2 marks)
The energy required to produce 1 mole of gaseous atoms from its elements in their standard states. Eg. ½ Cl2(g) --> Cl(g)
3) Define the term enthalpy of hydration (3 marks)
The energy released when 1 mole of gaseous ions is mixed with excess H2O to form dilute solution, until no more heat is evolved. Na+(g) + aq --> Na+(aq)
4) Construct an ionic equation to show the lattice energy of an ionic solid MX where M is a cation and X is an anion with charges of +1 and -1 respectively. (2 marks)
M+ (g) +X-(g) --> MX(s)
5) Why do lattice energy values differ for some compounds when calculated using the Born-Haber cycle and a purely ionic model? (2 marks)
This happens when the bond is partially covalent. The value of the lattice energy from the Born-Haber cycle will be greater than that from the purely ionic model. This usually occurs when the cation is very polarising or the anion very polarisable.
6) State two factors which affect the lattice energy of an ionic solid. (2 marks)
- Value of the charges
- Sum of radii of ions
7) Why is lattice energy and hydration energy exothermic? (1 mark)
This is due to the forces of attraction between the negative and positive ions. ???
[B]8) Express enthalpy of solution in terms of lattice energy and the hydration enthalpies of the ions. (2 marks)[/B]∆ Hsoln = -(lattice energy) + (hydration enthalpy of each cation + hydration enthalpy of each anion. )
9) Explain in terms of the hydration enthalpy of ions and lattice energy and your answer to 8) why the solubility of hydroxides increases down the group and why the solubility of sulphates decreases down the group. (6 marks)
As the cations size increases down the group, the enthalpy of hydration decreases. This is because the ionic radius increases down the group while the charge remains the same. Furthermore, because the radius of the hydroxide is similar to that of the cations, any increase in the size of the radius causes a considerable decrease in the value of the lattice energy. With reference to the above equation and the factors mentioned; the enthalpy of solution becomes considerably more exothermic as you go down the group.
As you go down the group, the solubility of the sulphates decreases. This is because the enthalpy of hydration decreases as the cations becomes bigger. Also, because the radius of the sulphate ion is much larger than the radius of any of the group 2 cations, the lattice energy only decreases slightly. Both these factors, cause the enthalpy of solution to become considerable less exothermic; thus decreasing the solubility of the group 2 ions down the group.
10) Would you expect enthalpy of atomisation of potassium to be more or less endothermic than lithium. Why? (2 marks)
Less endothermic because as you go down the group the size of the atom increases causing it to be easier to convert one mole of the atom in their standard state to one mole of the atom in the gas phase. ????
My model answers
1) Define the term lattice energy. (3 marks)
The exothermic enthalpy change when one mole of ionic solid is formed from its constituent gaseous ions.
2) Define the term enthalpy of atomisation (2 marks)
The enthalpy change when one mole of gaseous atoms is formed from the element in its most stable state under standard conditions, 1 atm pressure and 298K temperature.
3) Define the term enthalpy of hydration (3 marks)
The enthalpy change when one mole of gaseous ions is dissolved in excess water to form an infinitely dilute solution.
4) Construct an ionic equation to show the lattice energy of an ionic solid MX where M is a cation and X is an anion with charges of +1 and -1 respectively. (2 marks)
M+(g) + X-(g) ---> MX(s)
5) Why do lattice energy values differ for some compounds when calculated using the Born-Haber cycle and a purely ionic model? (2 marks)
Some ionic compounds have a small highly charged cation which can be highly polarising. If the anion has a large radius as well, this can lead to polarisation so the lattice energies will differ since the purely ionic model does not account for partial covalency of a compound.
6) State two factors which affect the lattice energy of an ionic solid. (2 marks)
Ionic charges
Sum of the ionic radii
7) Why is lattice energy and hydration energy exothermic? (1 mark)
Due to forces of attraction between oppositely charged cations and anions, i.e. bonds are formed.
8) Express enthalpy of solution in terms of lattice energy and the hydration enthalpies of the ions. (2 marks)
Enthalpy of solution = -lattice energy + sum of hydration enthalpies of ions
9) Explain in terms of the hydration enthalpy of ions and lattice energy and your answer to 8) why the solubility of hydroxides increases down the group and why the solubility of sulphates decreases down the group. (6 marks)
The group 2 cations have a similar ionic radius to the hydroxide anion. Therefore as we descend the group, the sum of the ionic radii increases sharply down the group, hence lattice energy decreases sharply. The enthalpy of hydration is independent of the anion and decreases down the group. The lattice energy decreases more than the sum of hydration enthalpies of ions. Hence enthalpy of solution becomes more exothermic down the group, so solubility of group 2 hydroxides increases down the group.
The group 2 cations have a small ionic radius compared to the sulphate anion. Therefore as we descend the group, the sum of the ionic radii changes very slightly, hence lattice energy also decreases slightly. The enthalpy of hydration is independent of the anion and decreases down the group. Sum of hydration enthalpies of ions decreases more than the lattice energy. Hence enthalpy of solution becomes more endothermic down the group, so solubility of group 2 sulphates decreases down the group.
10) Would you expect enthalpy of atomisation of potassium to be more or less endothermic than lithium. Why? (2 marks)
Less endothermic. The potassium atom has a larger radius than lithium, therefore lower charge density throughout metal structure, hence easier to separate atoms into gaseous phase.
1) Define the term lattice energy. (3 marks)
The exothermic enthalpy change when one mole of ionic solid is formed from its constituent gaseous ions.
2) Define the term enthalpy of atomisation (2 marks)
The enthalpy change when one mole of gaseous atoms is formed from the element in its most stable state under standard conditions, 1 atm pressure and 298K temperature.
3) Define the term enthalpy of hydration (3 marks)
The enthalpy change when one mole of gaseous ions is dissolved in excess water to form an infinitely dilute solution.
4) Construct an ionic equation to show the lattice energy of an ionic solid MX where M is a cation and X is an anion with charges of +1 and -1 respectively. (2 marks)
M+(g) + X-(g) ---> MX(s)
5) Why do lattice energy values differ for some compounds when calculated using the Born-Haber cycle and a purely ionic model? (2 marks)
Some ionic compounds have a small highly charged cation which can be highly polarising. If the anion has a large radius as well, this can lead to polarisation so the lattice energies will differ since the purely ionic model does not account for partial covalency of a compound.
6) State two factors which affect the lattice energy of an ionic solid. (2 marks)
Ionic charges
Sum of the ionic radii
7) Why is lattice energy and hydration energy exothermic? (1 mark)
Due to forces of attraction between oppositely charged cations and anions, i.e. bonds are formed.
8) Express enthalpy of solution in terms of lattice energy and the hydration enthalpies of the ions. (2 marks)
Enthalpy of solution = -lattice energy + sum of hydration enthalpies of ions
9) Explain in terms of the hydration enthalpy of ions and lattice energy and your answer to 8) why the solubility of hydroxides increases down the group and why the solubility of sulphates decreases down the group. (6 marks)
The group 2 cations have a similar ionic radius to the hydroxide anion. Therefore as we descend the group, the sum of the ionic radii increases sharply down the group, hence lattice energy decreases sharply. The enthalpy of hydration is independent of the anion and decreases down the group. The lattice energy decreases more than the sum of hydration enthalpies of ions. Hence enthalpy of solution becomes more exothermic down the group, so solubility of group 2 hydroxides increases down the group.
The group 2 cations have a small ionic radius compared to the sulphate anion. Therefore as we descend the group, the sum of the ionic radii changes very slightly, hence lattice energy also decreases slightly. The enthalpy of hydration is independent of the anion and decreases down the group. Sum of hydration enthalpies of ions decreases more than the lattice energy. Hence enthalpy of solution becomes more endothermic down the group, so solubility of group 2 sulphates decreases down the group.
10) Would you expect enthalpy of atomisation of potassium to be more or less endothermic than lithium. Why? (2 marks)
Less endothermic. The potassium atom has a larger radius than lithium, therefore lower charge density throughout metal structure, hence easier to separate atoms into gaseous phase.
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