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Topic: General Energy Calculations  (Read 30838 times)

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Offline Burner

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Re: General Energy Calculations
« Reply #45 on: April 08, 2016, 09:08:45 PM »
Yes
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Offline jamesbrown

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Re: General Energy Calculations
« Reply #46 on: April 09, 2016, 09:51:17 AM »
So the equation is q=102*0.0042*25.1
so q = 10.75..
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Q: Did you hear oxygen went on a date with potassium?
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Offline Burner

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Re: General Energy Calculations
« Reply #47 on: April 09, 2016, 10:06:23 AM »
Yes
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Offline jamesbrown

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Re: General Energy Calculations
« Reply #48 on: April 09, 2016, 11:02:34 AM »
So the next question is calculate the moles of copper sulphate reacting. So the mr is 160 and the mass is 100g so would it be 0.625 moles?
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Q: Did you hear oxygen went on a date with potassium?
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Offline Burner

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Re: General Energy Calculations
« Reply #49 on: April 09, 2016, 10:20:07 PM »
Quote from: jamesbrown on April 06, 2016, 07:22:04 AM
100cm3  of 0.20 mol/dm3 copper sulphate solution was put in a calorimeter and 2.0g of magnesium power added. The temperature of the solution rose by 25.1 °C.

(For convenience I quote the numbers given in here again)

Quote from: jamesbrown on April 09, 2016, 11:02:34 AM
So the next question is calculate the moles of copper sulphate reacting. So the mr is 160 and the mass is 100g so would it be 0.625 moles?

No. 100g is the mass of the solution which contains water and copper sulphate. You can't directly calculate the number of moles from this.

This problem involves the concept of limiting reagent. Start by calculating the number of moles of both copper sulphate and magnesium first. For a solution, the number of moles is given by (volume)*(molarity).
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Offline jamesbrown

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Re: General Energy Calculations
« Reply #50 on: April 10, 2016, 12:48:24 PM »
Why do I need to calculate the moles of magnesium because its not even part of the solution wouldn't it be better to calculate the moles of water and then the solution and then subtract. Also what do you mean by morality, is it another word for concentration?
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Offline Burner

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Re: General Energy Calculations
« Reply #51 on: April 11, 2016, 01:10:51 AM »
Quote from: jamesbrown on April 10, 2016, 12:48:24 PM
Why do I need to calculate the moles of magnesium because its not even part of the solution

Because you need to know which is the limiting reagent for this reaction(have you learnt that?)

Quote from: jamesbrown on April 10, 2016, 12:48:24 PM
wouldn't it be better to calculate the moles of water and then the solution and then subtract.

How?

Quote from: jamesbrown on April 10, 2016, 12:48:24 PM
Also what do you mean by morality, is it another word for concentration?

Yes.
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Offline jamesbrown

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Re: General Energy Calculations
« Reply #52 on: April 11, 2016, 09:45:41 AM »
No we dont know what a limiting reagent is sorry?
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Q: Did you hear oxygen went on a date with potassium?
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Offline Burner

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Re: General Energy Calculations
« Reply #53 on: April 11, 2016, 11:02:05 AM »
Oh... start reading from this: https://en.wikipedia.org/wiki/Limiting_reagent

And, write a balanced equation for the reaction first.

By the way, is this a high school homework or what? Your school didn't teach limiting reagent when teaching mole calculations?
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Year 1 science student in HKUST and a Chemistry geek.
If I make any mistakes in the forum, please don't hesitate to correct me as I want to learn.

Offline jamesbrown

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Re: General Energy Calculations
« Reply #54 on: April 11, 2016, 02:25:36 PM »
Its high school I don't think they did i can't remember. Could you link an easier tutorial Wikipedia is way too complex, or could you just explain it yourself?
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Offline mikasaur

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Re: General Energy Calculations
« Reply #55 on: April 11, 2016, 02:51:02 PM »
https://www.khanacademy.org/science/chemistry/chemical-reactions-stoichiome/limiting-reagent-stoichiometry/v/stoichiometry-limiting-reagent

It's a fairly basic concept. Let's say you have a cake recipe that uses 5 cups of flour and 1 cup of sugar. You have 10 cups of flour in your pantry and 3 cups of flour. Is flour or sugar going to be your "limiting reagent" in this case?
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Or you could, you know, Google it.

Offline jamesbrown

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Re: General Energy Calculations
« Reply #56 on: April 11, 2016, 07:24:42 PM »
Did you mean to say 10 cups of flour in  your pantry and 3 cups of sugar or is what you said correct?
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Q: Did you hear oxygen went on a date with potassium?
A: It went OK.

Offline mikasaur

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Re: General Energy Calculations
« Reply #57 on: April 11, 2016, 08:03:28 PM »
Yes. Sorry.

Don't worry too much about the analogy. That Khan Academy video should give you a good understanding of limiting reagents.
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Or you could, you know, Google it.

Offline jamesbrown

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Re: General Energy Calculations
« Reply #58 on: April 16, 2016, 11:20:44 AM »
I found out that the moles of copper sulphate was 20, because the volume is 100 and the density is 0.2 so there is 20 moles.
The the next question was what is the moles of magnesium, which I worked out to be 0.083, because ar = 24 and mass = 2.
But the next question was show that magnesium was in excess? can someone explain how to do this? is it empathy change. 
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Q: Did you hear oxygen went on a date with potassium?
A: It went OK.

Offline sjb

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Re: General Energy Calculations
« Reply #59 on: April 16, 2016, 06:02:08 PM »
What are the units of density? Not sure where you're finding the value of 0.2 for it either?
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