AS Chemistry question

In two similar, separate experiments the enthalpy changes for the reactions of sodium hydrogencarbonate and sodium carbonate with excess dilute HCl were determined.

Give TWO ways in which the temperature change differs when equal molar amounts of sodium hydrogencarbonate and sodium carbonate react similarly with the same volume of HCl.

Reply 1

Christophicus

OP

18

Widowmaker

In two similar, separate experiments the enthalpy changes for the reactions of sodium hydrogencarbonate and sodium carbonate with excess dilute HCl were determined.

Give TWO ways in which the temperature change differs when equal molar amounts of sodium hydrogencarbonate and sodium carbonate react similarly with the same volume of HCl.

anyone?

Reply 2

Abbas6

2

Widowmaker

anyone?

I thought it might have something to do with the size of the two anions, HCO3- being larger(?) than CO3- and so more polarisable. So a temperature change for NaHCO3 would be lower than that for NaCO3 because NaHCO3 would react quicker?? :confused:

But I'm not completely sure about this!

Reply 3

Christophicus

OP

18

abbasi

I thought it might have something to do with the size of the two anions, HCO3- being larger(?) than CO3- and so more polarisable. So a temperature change for NaHCO3 would be lower than that for NaCO3 because NaHCO3 would react quicker?? :confused:

But I'm not completely sure about this!

This question's quite hard!
Does anyone else have an idea?

Reply 4

Christophicus

OP

18

Duh! I've got it.
I just realised that the answer is in the previous part of the question!
Reaction of HCl with NaHCO3 is endothermic, so temperature change is negative. Reaction of HCl with Na2CO3 is exothermic so temperature change is positive.

Is that enough? because the question asks for two ways in which the temperature change differs.

Is it something to do with the fact that Na2CO3 reacts with 2 moles of HCl and NaHCO3 reacts with 1 moles of HCl?

AS Chemistry question

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