Question

Change in enthalpy for the following specific reaction. Be sure to indicate the correct sign (- or +) for the change in enthalpy. Reaction: Mg (s) + 2H+ (aq) ->> Mg2+ (aq) + H2 (g). I calculated -462 kJ.mol, but the answer on my calculations sheet gives a box for the answer from run 1 in Joules, answer from run 2 in Joules, and average enthalpy in Joules. Shouldn't the enthalpy be consistent regardless of the amount of Mg used?

Answer 1

Ans :

The enthalpy that you calculated has the units of KJ/mol , which means regardless of whatever amount of Mg used , you will get the same result (consistent) always , as you have fixed variable (mole) in it.

Now in the calculations sheet , they are not asking the enthalpy with respect to one mole (that you calculated) . They are asking the enthalpy according to the variable amount of Mg used , which will be different of each rum every time.

You keep on changing the amount of Mg in the reaction , and the enthalpy will also change. So these are two different things.

Hope this helps !!