park1996
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#1
Report Thread starter 7 years ago
#1
I know how to work out the enthalpy change in a question like this:

If 50 cm3 of 1.0 moldm-3 NaOH is added to 25 cm3 of 2.0 moldm-3 CH3COOH, the temperature rose by 8.3oC. Calculate the molar enthalpy change for the reaction.

My question is- what if the number of moles for each of the reactant were different. The no. of moles of NaOH and CH3COOH is 0.05moles, but what if they were different - say 50cm3 of CH3COOH, instead of 25cm3. How will you work the molar enthalpy change then.

**Also, when calculating the enthalpy change (not molar), then does concentration matter - if the one reactant had a greater no. of moles as a result of the concentration for example.

Please help! :confused:

Thx everyone
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Borek
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#2
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#2
Limiting reagent - calculate how many moles reacted. One you know how many moles reacted you can calculate molar enthalpy.
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park1996
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#3
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#3
(Original post by Borek)
Limiting reagent - calculate how many moles reacted. One you know how many moles reacted you can calculate molar enthalpy.
Could you answer my questions more specifically. I know this already
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Borek
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#4
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Trick is, I don't see where is the problem. You calculate heat from the temperature change, you calculate number of moles that reacted, you divide former by the latter. It is the same thing regardless of whether there is a limiting reagent present, or not.
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stu23
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#5
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(Original post by Borek)
Trick is, I don't see where is the problem. You calculate heat from the temperature change, you calculate number of moles that reacted, you divide former by the latter. It is the same thing regardless of whether there is a limiting reagent present, or not.
So if the question was 50cm3 of 2.0moldm-3, what would be the molar enthalpy change?
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Borek
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#6
Report 7 years ago
#6
(Original post by stu23)
So if the question was 50cm3 of 2.0moldm-3
Of what? Reacting with what? And in what amount?

I guess part of your problem is that you are seeing only part of the question, not trying to see everything given. List all data, and we will start from there.
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stu23
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#7
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(Original post by Borek)
Of what? Reacting with what? And in what amount?

I guess part of your problem is that you are seeing only part of the question, not trying to see everything given. List all data, and we will start from there.
What I'm trying to say is how would you calculate the molar enthalpy change, if the volume of CH3COOH was 50cm3, rather than 25cm3? I understand that this would mean a different no. of moles than the NaOH, but how would you calculate the change now?




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Borek
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#8
Report 7 years ago
#8
Calculate how many moles of acetic acid reacted with NaOH.

You were told that several times, no matter how many times you will ask this question, answer will always be identical - this is a limiting reagent problem.
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