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March 28, 2024, 11:07:59 pm

Author Topic: VCE Chemistry Question Thread  (Read 2313093 times)  Share 

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Bri MT

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Re: VCE Chemistry Question Thread
« Reply #7395 on: September 13, 2018, 01:24:47 pm »
+2
Hi everyone,
I know the exam is worth 60%, but i was wondering what a potential SS could be?
I don't have percents but I have grades
AOS 1
sac1 energy: B
sac2 rates and equillibirum: B+(I know that this was a high one)

AOS 2
sac 1 : food chem: A
sac 2 organic analysis A

Prac Poster A+

Hey,  it's really useful for us to know your rank (how well you did compared to your classmates) and predicted exam mark, if you want a predicted study score. 


Mark prediction isn't my strength,
but more information on this can be found in the Victorian Technical Score Discussion section of the forums :)

Sine

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Re: VCE Chemistry Question Thread
« Reply #7396 on: September 13, 2018, 10:13:57 pm »
+2
Hi everyone,
I know the exam is worth 60%, but i was wondering what a potential SS could be?
I don't have percents but I have grades
AOS 1
sac1 energy: B
sac2 rates and equillibirum: B+(I know that this was a high one)

AOS 2
sac 1 : food chem: A
sac 2 organic analysis A

Prac Poster A+
definitely not enough information for anyone to give you a study score prediction
Ideally for an accurate estimate you'd want to provide Unit3/4 Sac scores out of 100 along with your ranking in the cohort and cohort strength. In addition to this, a prediction of your exam score is useful.

hums_student

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Re: VCE Chemistry Question Thread
« Reply #7397 on: September 16, 2018, 09:15:16 pm »
0
Can someone help me with this question:

The density of ethanol is 0.785g/mL. The energy that would be available when 1.00L of ethanol was completely burned would be _____ ?

I think the answer is 23MJ but I'm not sure how to work it out.
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Sine

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Re: VCE Chemistry Question Thread
« Reply #7398 on: September 16, 2018, 09:19:52 pm »
+1
Can someone help me with this question:

The density of ethanol is 0.785g/mL. The energy that would be available when 1.00L of ethanol was completely burned would be _____ ?

I think the answer is 23MJ but I'm not sure how to work it out.
how did you get to 23MJ?

It seems correct but that's pretty redundant if you don't know how you got to it.


hums_student

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Re: VCE Chemistry Question Thread
« Reply #7399 on: September 16, 2018, 09:26:35 pm »
0
how did you get to 23MJ?

It seems correct but that's pretty redundant if you don't know how you got to it.
It was on an answer sheet our teacher gave out.

I'm not smart enough to work it out lol.

How would you work out this question?
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Bell9565

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Re: VCE Chemistry Question Thread
« Reply #7400 on: September 16, 2018, 10:21:53 pm »
+3
Can someone help me with this question:

The density of ethanol is 0.785g/mL. The energy that would be available when 1.00L of ethanol was completely burned would be _____ ?

I think the answer is 23MJ but I'm not sure how to work it out.

Okay so what you need to do is covert 1.00L to grams (via making it 1000mL and using the density), then using the data book work out how much energy is released as they give you ΔH for ethanol :)
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ANOXREDCAT

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Re: VCE Chemistry Question Thread
« Reply #7401 on: September 16, 2018, 10:45:56 pm »
+3
Can someone help me with this question:

The density of ethanol is 0.785g/mL. The energy that would be available when 1.00L of ethanol was completely burned would be _____ ?

I think the answer is 23MJ but I'm not sure how to work it out.

I've put my working out down below, but I wouldn't look at it till you've given it another go.
Spoiler
First, they are asking for enthalpy, meaning you need either mol or mass
Looking for mass in grams, let the amount of grams be x
since the density is 0.785g/mL, let 0.785=x/ml
Since there is 1000mL in a L, 0.785g=x/1000
then solve to get x=785g
Now, it say in the data book that the enthalpy of ethanol is 29.6 kJ/g
so multiply (785)(29.6), this gives 23236kJ. To convert that to MJ you need to divide by 1000.
This gives you 23MJ to two S.F
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hums_student

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Re: VCE Chemistry Question Thread
« Reply #7402 on: September 17, 2018, 05:51:05 pm »
0
Okay so what you need to do is covert 1.00L to grams (via making it 1000mL and using the density), then using the data book work out how much energy is released as they give you ΔH for ethanol :)
I've put my working out down below, but I wouldn't look at it till you've given it another go.
Spoiler
First, they are asking for enthalpy, meaning you need either mol or mass
Looking for mass in grams, let the amount of grams be x
since the density is 0.785g/mL, let 0.785=x/ml
Since there is 1000mL in a L, 0.785g=x/1000
then solve to get x=785g
Now, it say in the data book that the enthalpy of ethanol is 29.6 kJ/g
so multiply (785)(29.6), this gives 23236kJ. To convert that to MJ you need to divide by 1000.
This gives you 23MJ to two S.F

Thanks so much guys :)
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I\'m Not A Robot

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Re: VCE Chemistry Question Thread
« Reply #7403 on: September 19, 2018, 04:58:12 pm »
0
Hey, how do we go from kj/mol to kj/g??

As seen in this question:
When linoleic acid (C18H32O2) is burned it releases 8382 kj/mol. Convert 8382 kj/mol to kj/g.

Lear

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Re: VCE Chemistry Question Thread
« Reply #7404 on: September 19, 2018, 05:19:25 pm »
0
Divide by its molar mass
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I\'m Not A Robot

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Re: VCE Chemistry Question Thread
« Reply #7405 on: September 19, 2018, 06:37:42 pm »
0
Thank you! Also is it possible to calculate the calibration factor of a "calorimeter" using a chemical reaction; such as solid benzene. My textbook says that this is commonly used for bomb calorimeters but i was wondering if we could hypothetically use it for any calorimeter. I got a question on my SAC that asked us for a way to "calibrate our equipment to obtain more accurate results". Our experiment was pretty much burning a cracker to see how much of that energy was absorbed by the water placed in a can above it.

Sooo... could i say that "we could obtain more accurate results if we performed a chemical reaction such as  in the calorimeter that releases a known quantity of thermal energy and then measuring the resultant rise in temperature..."

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Re: VCE Chemistry Question Thread
« Reply #7406 on: September 19, 2018, 09:47:21 pm »
0
Thank you! Also is it possible to calculate the calibration factor of a "calorimeter" using a chemical reaction; such as solid benzene. My textbook says that this is commonly used for bomb calorimeters but i was wondering if we could hypothetically use it for any calorimeter. I got a question on my SAC that asked us for a way to "calibrate our equipment to obtain more accurate results". Our experiment was pretty much burning a cracker to see how much of that energy was absorbed by the water placed in a can above it.

Sooo... could i say that "we could obtain more accurate results if we performed a chemical reaction such as  in the calorimeter that releases a known quantity of thermal energy and then measuring the resultant rise in temperature..."
If there is any reaction with a known delta H value, then you can use it to find a calibration factor (CF). You use this CF to then increase the accuracy of the delta H values of any reactions that you test in that calorimeter. Therefore your statement is correct.
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mailman111

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Re: VCE Chemistry Question Thread
« Reply #7407 on: September 19, 2018, 10:27:33 pm »
0
Does anybody know where there are suggested solutions to the VCAA 2018 Northern Hemisphere exam from this June?
« Last Edit: September 19, 2018, 10:33:03 pm by mailman111 »

Vaike

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Re: VCE Chemistry Question Thread
« Reply #7408 on: September 20, 2018, 12:04:44 pm »
+3
Sooo... could i say that "we could obtain more accurate results if we performed a chemical reaction such as  in the calorimeter that releases a known quantity of thermal energy and then measuring the resultant rise in temperature..."

Yep, that would be a good response. Probably would just want to mention at the end of this response though that the purpose of doing that is so that a calibration factor can be calculated, which can then be used to determine the energy released by other reactions.

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Re: VCE Chemistry Question Thread
« Reply #7409 on: September 25, 2018, 07:39:38 pm »
0
Hey guys! I'm struggling to complete my notes responding to this dot point from the study design:
- the comparison of fossil fuels (coal, crude oil, petroleum gas, coal seam gas) and biofuels (biogas, bioethanol,
biodiesel) with reference to energy content, renewability and environmental impacts related to sourcing and
combustion

I've got the biofuels part but its difficult to organise my notes from the textbook for the fossil fuels part. Any help would be great!!