The Student Room Group

Chemistry question

Hi, please could i have help on this question? I thought the answer would be B to get the same number of moles as the one given for the same temperature change but the answer is C?
Here is the question: https://app.gemoo.com/share/image-annotation/597137458713653248?codeId=PYxE15xlXxme4&origin=imageurlgenerator
Thank you!
Original post by anonymous294
Hi, please could i have help on this question? I thought the answer would be B to get the same number of moles as the one given for the same temperature change but the answer is C?
Here is the question: https://app.gemoo.com/share/image-annotation/597137458713653248?codeId=PYxE15xlXxme4&origin=imageurlgenerator
Thank you!

You have to think in terms of the moles reacting and the volume being heated up.

If you react x mol of each and the total volume is V,
This will give the same temperature change as reacting 2x mol with a volume of 2V.

It is based on the equation: q = mcΔT (where q = energy, m = mass being heated, and ΔT is the temperature change)

In all cases c is constant (the specific heat capacity of the liquids)

therefore: ΔT depends on (is proportional to) q/m

and as m is directly proportional to V
ΔT depends on q/V

and as q is directly proportional to the number of moles reacting then:

ΔT is proportional to mol/V
Reply 2
Original post by charco
You have to think in terms of the moles reacting and the volume being heated up.

If you react x mol of each and the total volume is V,
This will give the same temperature change as reacting 2x mol with a volume of 2V.

It is based on the equation: q = mcΔT (where q = energy, m = mass being heated, and ΔT is the temperature change)

In all cases c is constant (the specific heat capacity of the liquids)

therefore: ΔT depends on (is proportional to) q/m

and as m is directly proportional to V
ΔT depends on q/V

and as q is directly proportional to the number of moles reacting then:

ΔT is proportional to mol/V

Thank you for this, but wouldn’t two times of the solution increase the temperature by 2 times?
Original post by anonymous294
Thank you for this, but wouldn’t two times of the solution increase the temperature by 2 times?

Read my answer - you are doubling the moles = doubling the energy
BUT you are doubling the mass being heated.

ΔT is proportional to mol/V
Reply 4
Original post by charco
Read my answer - you are doubling the moles = doubling the energy
BUT you are doubling the mass being heated.

ΔT is proportional to mol/V

Sorry thank you!

Quick Reply