HSC 2012-2015 Chemistry Marathon (archive) (2 Viewers)

[Ekman]

re: HSC Chemistry Marathon Archive

True, but briefly going over the method in a 5/6/7 marker will impress the hsc markers

Personally I reckon mentioning the Winkler titration method will impress them enough considering that its not in the syllabus. I think that talking about the actual process itself will be a waste of space and time.

 

[porcupinetree]

re: HSC Chemistry Marathon Archive

Personally I reckon mentioning the Winkler titration method will impress them enough considering that its not in the syllabus. I think that talking about the actual process itself will be a waste of space and time.

Fair enough - for a given question, there's probably more important things to focus on than Winkler. But if time is available, it'll add depth and sophistication

 

[Ekman]

re: HSC Chemistry Marathon Archive

I have a question for the people doing industrial chemistry.

I know that the K constant changes according to temperature, but how about pressure? My teacher said that a change in pressure will cause a change in temperature, hence cause a change in the K constant. However past papers say that pressure will not change the K constant. So what is correct? Ill give an example of an equation: The Contact Process: 2SO2 + O2 <---> 2SO3

Now we know that all of these are gases, so if there was an increase in pressure, wouldn't there be more products be favoured, hence the K constant should increase?

 

[Drsoccerball]

re: HSC Chemistry Marathon Archive

I have a question for the people doing industrial chemistry.

I know that the K constant changes according to temperature, but how about pressure? My teacher said that a change in pressure will cause a change in temperature, hence cause a change in the K constant. However past papers say that pressure will not change the K constant. So what is correct? Ill give an example of an equation: The Contact Process: 2SO2 + O2 <---> 2SO3

Now we know that all of these are gases, so if there was an increase in pressure, wouldn't there be more products be favoured, hence the K constant should increase?

I think change in pressure only increases collisions... I dont think that means that it increases in temperature?

 

[sharoooooo]

re: HSC Chemistry Marathon Archive

I have a question for the people doing industrial chemistry.

I know that the K constant changes according to temperature, but how about pressure? My teacher said that a change in pressure will cause a change in temperature, hence cause a change in the K constant. However past papers say that pressure will not change the K constant. So what is correct? Ill give an example of an equation: The Contact Process: 2SO2 + O2 <---> 2SO3

Now we know that all of these are gases, so if there was an increase in pressure, wouldn't there be more products be favoured, hence the K constant should increase?

http://community.boredofstudies.org/258/elective-industrial-chemistry/286877/why-k-only-affected-temperature.html

 

[Ekman]

re: HSC Chemistry Marathon Archive

I think change in pressure only increases collisions... I dont think that means that it increases in temperature?

Pressure does impact temperature. How else do refrigerators and air conditioners work?

 

[BlueGas]

re: HSC Chemistry Marathon Archive

I have a question for the people doing industrial chemistry.

I know that the K constant changes according to temperature, but how about pressure? My teacher said that a change in pressure will cause a change in temperature, hence cause a change in the K constant. However past papers say that pressure will not change the K constant. So what is correct? Ill give an example of an equation: The Contact Process: 2SO2 + O2 <---> 2SO3

Now we know that all of these are gases, so if there was an increase in pressure, wouldn't there be more products be favoured, hence the K constant should increase?

I was told that a change in pressure is considered has a change in concentration and since a change in concentration as no effect on K then pressure also has no effect on K. I've never heard of a change in pressure resulting in a change in temperature.

 

[Drsoccerball]

re: HSC Chemistry Marathon Archive

I was told that a change in pressure is considered as a change in concentration and since a change in concentration as no effect on K then pressure also has no effect on K. I've never heard of a change in pressure resulting in a change in temperature.

You misinterpreted what it was saying. When theres a change in pressure the amount of each reactant changes due to the size of the decrease/increase. When pressure is increased there is less room for the gas molecules to move so theres more collisions.

 

[leehuan]

re: HSC Chemistry Marathon Archive

What I think:

From Wikipedia:

If a gas's temperature increases, then so does its pressure if the mass and volume of the gas are held constant.
https://en.wikipedia.org/wiki/Gay–Lussac_law

In our situation, changing pressure is technically changing the volume of the vessel or the mass of the system (pumping in or out equilibrium mixture). This would technically cause the pressure-temperature proportionality to not necessarily be true.

 

[leehuan]

re: HSC Chemistry Marathon Archive

I've been taught pressure does not affect it anyway.

 

[BlueGas]

re: HSC Chemistry Marathon Archive

I've been taught pressure does not affect it anyway.

I'm sure everyone has lol.

 

[BlueGas]

re: HSC Chemistry Marathon Archive

Can someone tell me the chemistry behind the sulfide test used to identify heavy metals in water?

 

[Librah]

re: HSC Chemistry Marathon Archive

I have a question for the people doing industrial chemistry.

I know that the K constant changes according to temperature, but how about pressure? My teacher said that a change in pressure will cause a change in temperature, hence cause a change in the K constant. However past papers say that pressure will not change the K constant. So what is correct? Ill give an example of an equation: The Contact Process: 2SO2 + O2 <---> 2SO3

Now we know that all of these are gases, so if there was an increase in pressure, wouldn't there be more products be favoured, hence the K constant should increase?

Change in pressure doesn't necessarily mean increase in temperature, look up isothermal process. Even if pressure increases temperature, it's doing it indirectly and in the end your still arguing that it's temperature that changed the equilibrium constant, not pressure.

Equilibrium processes are defined using the 2nd law of thermodynamics (entropy and gibbs free energy). If you go look for the equilibrium constant derivation for ideal gases or solutions, you'll find that it's only dependent on temperature and some other constants that you don't have to know about.

If some smart-arse asks you why chemical reactions even occur, you can explain it using the second law of thermodynamics aswell. But there's no point learning this now, so just take everything for granted.

 

[BlueGas]

re: HSC Chemistry Marathon Archive

What products should I put when doing incomplete combustion reactants? If I put carbon dioxide, carbon monoxide, soot and water it gets kind of tedious balancing the reaction.

 

[Ekman]

re: HSC Chemistry Marathon Archive

What products should I put when doing incomplete combustion reactants? If I put carbon dioxide, carbon monoxide, soot and water it gets kind of tedious balancing the reaction.

Ive always kept them separate

 

[kawaiipotato]

re: HSC Chemistry Marathon Archive

You only have to put the products as water and one other pollutant molecule. I find it easy to just put the products as H2O and CO

 

[leehuan]

re: HSC Chemistry Marathon Archive

Don't put CO2 in for incomplete combustion.

As for the issue between C and CO, I reckon it's ok to put either or both. Some multiple choice questions in past HSCs have inserted both.
____________________
NEXT QUESTION:

Compare the chemistry of the dry cell or the lead-acid battery cell with another cell you have studied in terms of chemistry and applications. (4)

 

[BlueGas]

re: HSC Chemistry Marathon Archive

Don't put CO2 in for incomplete combustion.

As for the issue between C and CO, I reckon it's ok to put either or both. Some multiple choice questions in past HSCs have inserted both.
____________________
NEXT QUESTION:

Compare the chemistry of the dry cell or the lead-acid battery cell with another cell you have studied in terms of chemistry and applications. (4)

Sorry for interrupting but I just wanna ask a question for clarification (it's probably a really simple question anyway), CFC is known to be inert so it is able to diffuse into the stratosphere without reacting in the troposphere, since it's inert, how does it react with ozone?

 

[sy37]

re: HSC Chemistry Marathon Archive

Sorry for interrupting but I just wanna ask a question for clarification (it's probably a really simple question anyway), CFC is known to be inert so it is able to diffuse into the stratosphere without reacting in the troposphere, since it's inert, how does it react with ozone?

CFCs don't react with anything per se, rather they are decomposed by short wavelength UV rays. This decomposition process releases chlorine free radicals from the CFCs. It is these chlorine free radicals that react with ozone.

The reaction of this chlorine free radical with an ozone molecule produces oxygen gas and a chlorine monoxide free radical.

THEN, it is this chlorine radical again that reacts with ozone to produce oxygen gas and a chlorine monoxide free radical.

The reaction of this chlorine free radical with an ozone molecule produces oxygen gas and a chlorine monoxide free radical.

THEN, it is this chlorine radical again that reacts with ozone to produce oxygen gas and a chlorine monoxide free radical.

it's a cycle! The chlorine radical acts as a catalyst

 

[BlueGas]

re: HSC Chemistry Marathon Archive

CFCs don't react with anything per se, rather they are decomposed by short wavelength UV rays. This decomposition process releases chlorine free radicals from the CFCs. It is these chlorine free radicals that react with ozone.

The reaction of this chlorine free radical with an ozone molecule produces oxygen gas and a chlorine monoxide free radical.

THEN, it is this chlorine radical again that reacts with ozone to produce oxygen gas and a chlorine monoxide free radical.

The reaction of this chlorine free radical with an ozone molecule produces oxygen gas and a chlorine monoxide free radical.

THEN, it is this chlorine radical again that reacts with ozone to produce oxygen gas and a chlorine monoxide free radical.

it's a cycle! The chlorine radical acts as a catalyst

Ah that's what I misunderstood, I thought it was CFCs reacting with ozone directly, I forgot they first react with UV lol.