[AbbyCd]

I just conducted a lab in which I am testing varying amounts of magnesium to react with a consistent amount of hydrochloric acid, determining which amount of magnesium produces a reaction whose enthalpy is the closest to the theoretical/ideal enthalpy of this equation. I created 3 conditions using 0.025 mols Mg, 0.020 mols Mg, and 0.017 mols Mg. 0.017 mols produced the closest to the theoretical enthalpy, then 0.020, then 0.025 being the least accurate. I am completely lost as to why this would be! Could anyone provide some sort of scientific explanation that is responsible for my data? Why does the least amount of Mg yield the most accurate enthalpy?
Additional info just in case you need it to answer:
Balanced equation: Mg + 2HCl ------> MgCl2 + H2 (can't do subscript)
I used 50 mL HCl with a concentration of 1 mol Hcl per 1 L HCl(aq)
Thanks all! Also this is urgent because my lab is due tomorrow

[orthoformate]

I just conducted a lab in which I am testing varying amounts of magnesium to react with a consistent amount of hydrochloric acid, determining which amount of magnesium produces a reaction whose enthalpy is the closest to the theoretical/ideal enthalpy of this equation. I created 3 conditions using 0.025 mols Mg, 0.020 mols Mg, and 0.017 mols Mg. 0.017 mols produced the closest to the theoretical enthalpy, then 0.020, then 0.025 being the least accurate. I am completely lost as to why this would be! Could anyone provide some sort of scientific explanation that is responsible for my data? Why does the least amount of Mg yield the most accurate enthalpy?
Additional info just in case you need it to answer:
Balanced equation: Mg + 2HCl ------> MgCl2 + H2 (can't do subscript)
I used 50 mL HCl with a concentration of 1 mol Hcl per 1 L HCl(aq)
Thanks all! Also this is urgent because my lab is due tomorrow

What values did you get for each condition? How did you measure each condition?

[AbbyCd]

What values did you get for each condition? How did you measure each condition?
[/quote]
I used the average change in temperature of all 3 trials for each condition, then used these averages to calculate/publish 3 enthalpies (one for each condition). 0.025 mols Mg was -293.4 kj/mol, 0.020 mols Mg was -335.8 kj/mol, and 0.017 mols was -360.2 kj/mol (the theoretical enthalpy is -464 kj/mol). Thanks!

[Borek]

Please describe the procedure that you have followed.

[Enthalpy]

50mmol HCL would have just sufficed, but maybe this went wrong.

Did some water boil off? At 1mol/L it shouldn't if starting cold, but the temperature rise is significant.

How do you compute the heat of the reaction, especially the heat of formation of the HCl solution? Gaseous HCL has already a heat of formation, and dissolving it releases significant heat.

[orthoformate]

Please describe the procedure that you have followed.

This is important. It would help if you could provide us with a copy of your lab notebook.