A student added 1.2 g of magnesium turnings to 100 ml of 1M HCl in a styrofoam cup calorimeter. The initial temperature of HCl was 24C and the final temperature of the solution was 50C What is the q?

Question

1. Calculate the enthalpy of reaction

Answer 1

(q) = mC∆T

Since the problem doesn't provide the mass or density of HCl nor the specific heat of HCl, certain assumptions will be made.

q = heat = ?

m = mass = 100 ml x 1g/ml = 100 g (IF WE ASSUME DENSITY OF HCl IS SAME AS WATER = 1g/ml)

∆T = change in temperature = 50º - 24º = 26º

C = specific heat of HCl = 4.184 J/gº (IF WE ASSUME IT IS THE SAME AS THAT FRO WATER)

q = (100 g)(4.184 J/gº)(26º)

q = -10,878 J (sig.figs. ignored) . Note the negative sign indicating an exothermic reaction since temp rose.

If you want the molar change in enthalpy, you'd find moles of Mg and divide q by that value.

Mg + 2HCl ==> MgCl2 + H2(g)