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Enthalpy change question help!

Completely stuck on part b

2) The temperature rise when excess zinc was added to copper sulfate was found to be 10 degrees celcius

Heat transferred: 25 x 4.18 x 10 J

(a) What two assumptions did they make in this calculation (done this)

(b) If the concentration of the copper sulfate solution was 0.1dm^-3 what would be the enthalpy change for this reaction (delta Hr)?
The enthalpy change is just the heat transferred (under constant pressure) divided by the number of moles of substance used :smile:
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somalia99
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Original post by EierVonSatan
The enthalpy change is just the heat transferred (under constant pressure) divided by the number of moles of substance used :smile:


Tried that, got completely a wrong answer lol!

1045 (from MCdeltaT) divided by 0.156 moles (from 25 grams of CuSO4 divided by RFM of CuSO4) and I got 6667jmol-1 when the answer is -418jmol-1 :s
Original post by somalia99
Tried that, got completely a wrong answer lol!

1045 (from MCdeltaT) divided by 0.156 moles (from 25 grams of CuSO4 divided by RFM of CuSO4) and I got 6667jmol-1 when the answer is -418jmol-1 :s


25 g refers to the water heated (you use the heat capacity of water!)

You have 25 mL of solution (assume 1 g = 1 mL) and you know the concentration, so you can find the number of moles :smile:
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somalia99
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Original post by EierVonSatan
25 g refers to the water heated (you use the heat capacity of water!)

You have 25 mL of solution (assume 1 g = 1 mL) and you know the concentration, so you can find the number of moles :smile:


I am a bit confused lol, isn't the SHC of water 4.18? :tongue:
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somalia99
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Original post by EierVonSatan
25 g refers to the water heated (you use the heat capacity of water!)

You have 25 mL of solution (assume 1 g = 1 mL) and you know the concentration, so you can find the number of moles :smile:


Ah, I see it now, thank you for your help EVS (y)
Original post by somalia99
I am a bit confused lol, isn't the SHC of water 4.18? :tongue:


Yes :tongue:

Q = mcΔT = mass of water x heat capacity of water x temperature change of the water

It's all about water, you've taken 25 g as the mass of the copper sulfate - that's why you've got the wrong answer.

Ah ok, good :smile: Welcome.

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