Lab Questions help! INFO: Final Temperature: 36.3 degrees C Initial Temperature:

Question

Lab Questions help!

INFO:

Final Temperature: 36.3 degrees C

Initial Temperature: 23.7 degrees C

Temperature Change: 12.6 degrees C

30mL HCl

0.103g mg used.

Calculations should be based on this part of the experiment

Mg(s) + 2HCl (aq) ---------> H2 + MgCl2 (aq)

1. Determine the enthalpy of reaction, delta Hrxn, using enthalpy of formation data from appendix J in your text book

2. is the predicted reatcion endo or exothermic? explain.

3. Deterine the limiting reaction for this reaction.

4. determind the energy based on the enthalpy of reaction and moles of limiting reactant.

5. Determine the theoretical temperature change for this reaction ( use the specific heat of water 4.184 J/g * degrees C and Density of 1.000gmL for HCl

Explanation / Answer

In fact the reaction is

Mg(s) + 2H+(aq) ---------> H2 + Mg2+

1.

Enthalpy of reaction = dHof, Mg2+(aq)     (all other dHof are 0)

Please verify the values from your Table.

dHrxn = 466.85 kJ/mol

2.

The reaction is exothermic. The final temperature is higher.

3.

The concentration of HCl is missing., but I suppose it is about 1M (about 0.03 mol in 30 mL; it can’t be very diluted).

0.103g Mg / 24.3 g/mol = 0.00423 mol Mg. I propose it as limiting reagent.

4.

Qreleased = 0.00423mol x (466.85 kJ/mol) = 1.975 kJ

5.

Q = m x c x dT

dT = Q/(mxc) = 1.975 kJ / (30 gx4.184 J/g. ºC )= 15.7 ºC

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