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# Help with chemistry question please! Watch

1. Magnesium will also displace copper from copper (II) sulphate solution.If an excess of magnesium is added to 100 cm3 of1.0 moldm-3 copper(II) sulphate, the temperature increases by 46.3 oC.
a) Calculate the molar enthalpy change for the reaction

b) Calculate the minimum quantityof magnesium required to ensure it is in excess.

c) Calculate the temperature change if only 0.8g of magnesium is added.

So I got -1935.34 for a, which is wrong and i got completely wrong answers for b and c!!! Can someone explain how to work them out please?

Here are my working for a)
q= mcΔT
q= 100 x 4.18 x 46.3
q= 19353.4 J
q= 19.3534 KJ
moles= conc x vol
moles= 0.100 x 0.100 = 0.0100moles
So enthalpy change = 19.3534/0.0100
= -1935.34 kJmol-1

Can someone please tell we where I went wrong here with the calculation above?
I'm not going to even bother showing my workings for b and c because they are completely wrong and I'm not certain how to work them out anyway (I had an 'educational' guess).

Any help would be greatly appreciated... + REP
2. (Original post by RedRosesBloom)
Magnesium will also displace copper from copper (II) sulphate solution.If an excess of magnesium is added to 100 cm3 of1.0 moldm-3 copper(II) sulphate, the temperature increases by 46.3 oC.
a) Calculate the molar enthalpy change for the reaction

b) Calculate the minimum quantityof magnesium required to ensure it is in excess.

c) Calculate the temperature change if only 0.8g of magnesium is added.

So I got -1935.34 for a, which is wrong and i got completely wrong answers for b and c!!! Can someone explain how to work them out please?

Here are my working for a)
q= mcΔT
q= 100 x 4.18 x 46.3
q= 19353.4 J
q= 19.3534 KJ
moles= conc x vol
moles= 0.100 x 0.100 = 0.0100moles
So enthalpy change = 19.3534/0.0100
= -1935.34 kJmol-1

Can someone please tell we where I went wrong here with the calculation above?
I'm not going to even bother showing my workings for b and c because they are completely wrong and I'm not certain how to work them out anyway (I had an 'educational' guess).

Any help would be greatly appreciated... + REP
In the question it says the solution is 100 cm^3 and 1 M so that would give 0.1 moles not 0.01
3. (Original post by RedRosesBloom)
Magnesium will also displace copper from copper (II) sulphate solution.If an excess of magnesium is added to 100 cm3 of1.0 moldm-3 copper(II) sulphate, the temperature increases by 46.3 oC.
a) Calculate the molar enthalpy change for the reaction

b) Calculate the minimum quantityof magnesium required to ensure it is in excess.

c) Calculate the temperature change if only 0.8g of magnesium is added.

So I got -1935.34 for a, which is wrong and i got completely wrong answers for b and c!!! Can someone explain how to work them out please?

Here are my working for a)
q= mcΔT
q= 100 x 4.18 x 46.3
q= 19353.4 J
q= 19.3534 KJ
moles= conc x vol
moles= 0.100 x 0.100 = 0.0100moles
So enthalpy change = 19.3534/0.0100
= -1935.34 kJmol-1

Can someone please tell we where I went wrong here with the calculation above?
I'm not going to even bother showing my workings for b and c because they are completely wrong and I'm not certain how to work them out anyway (I had an 'educational' guess).

Any help would be greatly appreciated... + REP
All you did was misread the question! You used 0.1 moldm^-3 instead of 1.0 moldm^-3
4. (Original post by langlitz)
In the question it says the solution is 100 cm^3 and 1 M so that would give 0.1 moles not 0.01
(Original post by rosemondtan)
All you did was misread the question! You used 0.1 moldm^-3 instead of 1.0 moldm^-3
Oops, didn't realise, thank you! I hope I don't do this in the exam, because I always seem to end up misreading the questions *facepalm* :P
5. (Original post by RedRosesBloom)
Oops, didn't realise, thank you! I hope I don't do this in the exam, because I always seem to end up misreading the questions *facepalm* :P
Stay calm and you will be fine
6. (Original post by rosemondtan)
Stay calm and you will be fine
Easier said than done, although I will try. I think I will need to read the question several times, just to make sure xD

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