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A-Level Chemistry

I have a few entropy related questions:

Does the hydrogen bonding in Hf effect the entropy or enthalpy of the dissociation of hydrofluoric acid? The textbook I use says it's related to entropy but doesn't explain how. If entropy, please explain how.

Why is there a difference in entropy of a liquid and an aqueous solution?

Finally I need so general help for chemistry. I'm tying to push my grade to an A* btu I can't get past the 85% mark on most of my topic test or AS mocks. I feel as if I've done loads of practice questions and mainly understand the content but still get around the 80% mark. How can I improve this?

Thank you to anyone who answers. :smile:
Original post by zushi1248
I have a few entropy related questions:
Does the hydrogen bonding in Hf effect the entropy or enthalpy of the dissociation of hydrofluoric acid? The textbook I use says it's related to entropy but doesn't explain how. If entropy, please explain how.
Why is there a difference in entropy of a liquid and an aqueous solution?
Finally I need so general help for chemistry. I'm tying to push my grade to an A* btu I can't get past the 85% mark on most of my topic test or AS mocks. I feel as if I've done loads of practice questions and mainly understand the content but still get around the 80% mark. How can I improve this?
Thank you to anyone who answers. :smile:

What topic is this in the specification ?
Reply 2
Original post by kmat1893
What topic is this in the specification ?

I take edexcel chemistry topic 13
Original post by zushi1248
I take edexcel chemistry topic 13

Same, what are you predicted at the moment ?
Original post by zushi1248
I have a few entropy related questions:

Does the hydrogen bonding in Hf effect the entropy or enthalpy of the dissociation of hydrofluoric acid? The textbook I use says it's related to entropy but doesn't explain how. If entropy, please explain how.

Why is there a difference in entropy of a liquid and an aqueous solution?

Finally I need so general help for chemistry. I'm tying to push my grade to an A* btu I can't get past the 85% mark on most of my topic test or AS mocks. I feel as if I've done loads of practice questions and mainly understand the content but still get around the 80% mark. How can I improve this?

Thank you to anyone who answers. :smile:

Entropy can be viewed (rather simplistically) as a sort of measure of how disordered the particles in a substance are.

Since fluoride ions are capable of hydrogen bonding, dissolving sources of them (e.g HF, NaF) in water tends to result in a decrease in ΔS(system) as the new, stronger hydrogen bonds organise the surrounding solvent molecules. I would guess the dissociation of HF in water results in a decrease in ΔS(system) because of the very strong attraction between the F^- and H3O^+ ions that would also organise the system.

In terms of enthalpy, the H-F bond is pretty short and pretty stable, so it has quite a high bond enthalpy. This makes HF quite a weak acid. This is nothing to do with hydrogen bonding, however.

I’m not quite sure what you mean by your next question, but my interpretation is along the lines of “which has a more positive (standard molar) entropy: a substance dissolved in water or a (pure) liquid?”. If my interpretation is correct, more often than not, I would expect the liquid to have the greater standard molar entropy, since the solute and the solvent molecules will attract, imposing order on the system and therefore decreasing the entropy.

Have you tried using examiner’s reports after attempting questions to understand how common errors arise in commonly assessed styles of questions or keeping a log of questions you’ve lost marks on (and why) and re-attempting them after revisiting the relevant topics?

I also used to encourage the students I used to mentor to underline key words and information in the question so ask to keep track of them and to ensure they did as the question asked. Speaking of which, there is an appendix of command words used in the exams and what they mean somewhere in the specification for Edexcel A level chemistry and I advise you to print that page alone out and put it up somewhere visible in your room.
(edited 1 month ago)
Reply 5
Original post by kmat1893
Same, what are you predicted at the moment ?

A*AA

The 2 A are bio and chem A* in maths
Reply 6
Original post by TypicalNerd
Entropy can be viewed (rather simplistically) as a sort of measure of how disordered the particles in a substance are.
Since fluoride ions are capable of hydrogen bonding, dissolving sources of them (e.g HF, NaF) in water tends to result in a decrease in ΔS(system) as the new, stronger hydrogen bonds organise the surrounding solvent molecules. I would guess the dissociation of HF in water results in a decrease in ΔS(system) because of the very strong attraction between the F^- and H3O^+ ions that would also organise the system.
In terms of enthalpy, the H-F bond is pretty short and pretty stable, so it has quite a high bond enthalpy. This makes HF quite a weak acid. This is nothing to do with hydrogen bonding, however.
I’m not quite sure what you mean by your next question, but my interpretation is along the lines of “which has a more positive (standard molar) entropy: a substance dissolved in water or a (pure) liquid?”. If my interpretation is correct, more often than not, I would expect the liquid to have the greater standard molar entropy, since the solute and the solvent molecules will attract, imposing order on the system and therefore decreasing the entropy.
Have you tried using examiner’s reports after attempting questions to understand how common errors arise in commonly assessed styles of questions or keeping a log of questions you’ve lost marks on (and why) and re-attempting them after revisiting the relevant topics?
I also used to encourage the students I used to mentor to underline key words and information in the question so ask to keep track of them and to ensure they did as the question asked. Speaking of which, there is an appendix of command words used in the exams and what they mean somewhere in the specification for Edexcel A level chemistry and I advise you to print that page alone out and put it up somewhere visible in your room.

Wow okay I will lock for it, thanks a lot for the tips 😁

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