[mouk92]

This is the question

Magnesium will also displace copper from copper (II) sulphate solution. If an excess of magnesium is added to 100 cm3 of 1.0 moldm-3 copper(II) sulphate, the temperature increases by 46.3 oC.

a)   Calculate the molar enthalpy change for the reaction.  ( i got the answer to be -193.534 KJmol ^-1  )

However im stuck on the rest of this question...

b)   Calculate the minimum quantity of magnesium required to ensure it is in excess.
c)   Calculate the temperature change if only 0.8 g of magnesium is added.


thanks.

[Borek]

Simple stoichiometry for b - start with the reaction equation.

[mouk92]

ill be honest and say i dont know what that is

[zeoblade]

Rather than create even more threads I thought I'd post here since it's kind of related to this thread.

Energy total = energy potential + energy kinetic + energy internal

In the lab, we're not displacing so both energy potential is constant and energy kinetic = 0 leaving energy internal the component of interest in this situation. Energy internal (U) combined with pressure-volume work (PV) = enthalpy (H). Rearranging this equation U = H - PV but now I don't know how to define U because H is dependent on U and PV. I can see that -PV is from rearrangement of the equation but the negative value means the system is using energy to do work so that energy leaves the system to increase volume assuming constant pressure. Is this interpretation, correct or incorrect?

U component of energy total also has energy potential + energy kinetic within it that adds onto the greater energy potential + energy kinetic to create energy total. Now U can also be expressed as heat (q) + work (w). Is this the same work as H = U + PV? When U = q + w, w can also be defined as PV. Is the sign also -PV because q is being converted to w(PV) and leaves to system to give -PV?

This scenario is for exothermic reactions, so for endothermic reactions do we need to change the sign of H = U + PV --> H = U - PV and U = q + w --> U = -q - w?

I'm ashamed to admit I lost myself in all the steps and need to grasp the big picture again because the terminology of the components have such similar meaning. Can I differentiate H = U + PV as greater and U = q + w(-PV or -pv) as lesser? Is the U in H = U + PV the same U in U = q + w? Or is it different like U and u?