HSC 2012-2015 Chemistry Marathon (archive) (6 Viewers)

[ziaa]

Re: HSC 2012 Chemistry Marathon

Hi guys, this is a question from the 2009 HSC -
Question 20:
Calculate the mass of ethanol that must be burnt to increase the temp of 210g of water by 65 degrees celsius if exactly half of teh heat released by this combustion is lost to its surroundings.
Heat of combustion = 1367 kj/mol/L

many thanks in advance

 

[nightweaver066]

Re: HSC 2012 Chemistry Marathon

Hi guys, this is a question from the 2009 HSC -
Question 20:
Calculate the mass of ethanol that must be burnt to increase the temp of 210g of water by 65 degrees celsius if exactly half of teh heat released by this combustion is lost to its surroundings.
Heat of combustion = 1367 kj/mol/L

many thanks in advance

If half the heat is lost to the surroundings, you'll need to produce double the amount of heat.

That means you'll need of energy



Finding molar heat of combustion of ethanol:





As we know this is 1367kJ/mol,



Rearrange and solve for m.

Question:

 

[kingkong123]

Re: HSC 2012 Chemistry Marathon

Question:

(i) According to the Bronsted-Lowry Theory of acids and bases, an acid is a proton donor and a base is a proton acceptor.
(ii) In reaction (1), acts as a base. It accepts a proton from , resulting in the . In reaction (2) acts as an acid, it donates a proton to , resulting in the in the reactants.

 

[Aesytic]

Re: HSC 2012 Chemistry Marathon

In reaction 1, HCO3- acts as a bronsted-lowry base; it accepts a proton from the hydronium ion on the RHS to form H2CO3

 

[nightweaver066]

Re: HSC 2012 Chemistry Marathon

*revive*

 

[nightweaver066]

Re: HSC 2012 Chemistry Marathon

Bump

 

[barbernator]

Re: HSC 2012 Chemistry Marathon

a)

b) both of these steps increase the efficiency of the esterification reaction. The concentrated sulfuric acid acts as a catalyst to reduce the activation energy for the reactants, and the refluxing process allows the reaction to occur at a higher temperature, and increases the rate of reaction. The condenser in the process ensures that reactants and products are kept within the flask.

 

[barbernator]

Re: HSC 2012 Chemistry Marathon



how do u attach photos properly?

 

[nightweaver066]

Re: HSC 2012 Chemistry Marathon

a) View attachment 24856

b) both of these steps increase the efficiency of the esterification reaction. The concentrated sulfuric acid acts as a catalyst to reduce the activation energy for the reactants, and the refluxing process allows the reaction to occur at a higher temperature, and increases the rate of reaction. The condenser in the process ensures that reactants and products are kept within the flask.

Since it says justify, you should include that the esterification process is very slow.

For the last point you made, mention how the reactants and products are volatile.

Other than that, good

 

[nightweaver066]

Re: HSC 2012 Chemistry Marathon

View attachment 24859

how do u attach photos properly?

Use link [./IMG] without the dot

[tex]NH_4Cl $ is the product of ammonium hydroxide and hydrochloric acid$\\NH_4OH_{(aq)} + HCl_({aq)} \rightarrow NH_4Cl_{(aq)}\\$As it is a product of a weak base and strong acid, the product must be acidic, i.e. it forms an acidic salt such that:$\\ NH^+_{4(aq)} + H_2O_{(l)} \rightarrow NH_3{(aq)} + H_3O_{(aq)}^+[/tex]

 

[mirakon]

Re: HSC 2012 Chemistry Marathon

Chem notes uploaded onto year 12 chit chat

 

[nightweaver066]

Re: HSC 2012 Chemistry Marathon

^^^
Check it out if you guys need it.

New question:

 

[barbernator]

Re: HSC 2012 Chemistry Marathon

 

[nightweaver066]

Re: HSC 2012 Chemistry Marathon

u should probably include water as a product in this equation as well but all good

Oops.. Main point was gotten across though

 

[barbernator]

Re: HSC 2012 Chemistry Marathon

ethene is produced through the dehydration of ethanol, as well as cracking, both catalytic and thermal. A variety of petrochemical feedstocks can be converted into ethanol. Biomass, containing cellulose is broken down into glucose monomers through using bacteria or sulfuric acid catalysts. This can then be processed into ethanol through fermentation by yeast. Yeast is then dehydrated (insert equation here) using (a concentrated sulfuric acid catalyst i think....) into ethylene. Long chain alkanes, sourced from crude oil, are cracked into smaller alkanes and alkenes. Thermal cracking and catalytic cracking both produce these products, (equation pentane -- ethene and propane). I think i have missed heaps in this answer, but hopefully it covers the two main processed for the production of ethanol. Im surprised it isnt worth more marks actually

Edit: I think i've interpretted "petrochemical feedstocks" incorrectly not sure...

 

[nightweaver066]

Re: HSC 2012 Chemistry Marathon

ethene is produced through the dehydration of ethanol, as well as cracking, both catalytic and thermal. A variety of petrochemical feedstocks can be converted into ethanol. Biomass, containing cellulose is broken down into glucose monomers through using bacteria or sulfuric acid catalysts. This can then be processed into ethanol through fermentation by yeast. Yeast is then dehydrated (insert equation here) using (a concentrated sulfuric acid catalyst i think....) into ethylene. Long chain alkanes, sourced from crude oil, are cracked into smaller alkanes and alkenes. Thermal cracking and catalytic cracking both produce these products, (equation pentane -- ethene and propane). I think i have missed heaps in this answer, but hopefully it covers the two main processed for the production of ethanol. Im surprised it isnt worth more marks actually

Edit: I think i've interpretted "petrochemical feedstocks" incorrectly not sure...

I think you have as well.

"Petrochemical feedstocks" = petroleum.

Maybe reattempt the question with a focus on catalytic/thermal cracking? (Go through the process and provide balanced chemical equations)

Good attempt though if it was simply ways of attaining ethene

 

[barbernator]

Re: HSC 2012 Chemistry Marathon

heres an abstract one 24875 [img]

lol fail attachment again

 

[barbernator]

Re: HSC 2012 Chemistry Marathon

1. Explain why the equivalence point of a reaction doesn't necessarily result in the pH of the solution being 7 at that point. (2)
2. From this, write a balanced equation for an acid-base neutralisation reaction with a equivalence point of pH>7 and state the indicator which is used to show this point in this reaction. (2)

 

[nightweaver066]

Re: HSC 2012 Chemistry Marathon

Your first question. I don't have time so i'll just run over a few points.
- Petroleum is a finite resource and we are consuming it quicker than we're excavating it
- Experts predict it will run out in the next 50 years
- Oxidation-reduction reactions are able to produce a voltage and supply electricity and with further scientific development has the potential to substitute petroleum for energy
- Lead-acid cells is one important battery used today
- Used to jump-start cars and as a power source for rural areas
- Oxidation reaction & reduction equation formula
- Petroleum running out -> alternative needed -> batteries using oxidation-reduction reactions are becoming more important -> must improve technology so that batteries can be more efficient and can be used for more large scale applications

1. The equivalence point of a reaction depends upon the titrant and the titre. A reaction between a strong base and strong acid or a weak acid and weak base will yield a neutral solution, i.e. pH of 7. However reactions between a strong base and weak acid or weak base and strong acid will yield either pH < 7 or pH > 7 respectively. Therefore the equivalence point of a reaction doesn't necessarily result in the pH of the solution being 7 at that point.

2. Using NaOH and acetic acid,


Use phenolphthalein to determine the equivalence point.

 

[nightweaver066]

Re: HSC 2012 Chemistry Marathon

Question: