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# calorimetry/enthalpy change question Watch

NaHCO3 + HCl --> NaCl + H2O + CO2

3.53g sodium hydrogencarbonate was added to 30cm3 of 2mol/dm3 hydrochloric acid. The temperature fell by 10.3C. Work out which reagent was in excess and then calculate the energy change in kJ/mol.

This is what I did:
HCl: 0.03dm3 * 2mol/dm3 = 0.06 mol
NaHCO3: 0.06 mol should react (equation) but with the calculation (moles = mass/Mr) 0.04202... moles are present
So HCl is in excess

Q=mc#T
Q = 30 * 4.2 * 10.3 = 1297.8J = 1.2978kJ

enthalpy change: 1.2978/0.04.. = +30.8kJ/mol

*I got confused with which value for moles I was meant to use??*
THANKS x
2. bump?
3. (Original post by surina16)
bump?
Its fine assuming you havent made any arithmetic errors (i assumed you typed in everything correctly)
4. (Original post by samb1234)
Its fine assuming you havent made any arithmetic errors (i assumed you typed in everything correctly)
great thank you i was just unsure if I was meant to use 0.06 or 0.042.. for moles at the end

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