The Student Room Group
Competition - post a photo you've taken of nature >>
Competition - post a photo you've taken of nature >>
Competition - post a photo you've taken of nature >>

Enthalpy help!

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 :smile:
Reply 1
Avatar for Borek
Borek
4
Limiting reagent - calculate how many moles reacted. One you know how many moles reacted you can calculate molar enthalpy.
Reply 2
Avatar for park1996
park1996
OP
2
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
Reply 3
Avatar for Borek
Borek
4
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.
Reply 4
Avatar for stu23
stu23
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?
Reply 5
Avatar for Borek
Borek
4
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.
Reply 6
Avatar for stu23
stu23
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?




Reply 7
Avatar for Borek
Borek
4
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.

Quick Reply

Related discussions

Latest

Trending

Trending

Articles for you