Question

Find the enthalpy of combustion of magnesium using Hess' Law. Assume that 100 mL of HCl was used in each trial and that HCl is in excess:

Given data:
grams of magnesium= 0.244 g
Final temp=32.2 degrees celsius
Initial temp= 21.3 degrees celsius

Answer 1

q=(mass of HCL)*4.18*(Tf-Ti)
100 ml is 100g
specific heat capacity of the reaction mixture assumed to be the same as water,
ie, specific heat capacity = 4.184 JK-1g-1
Number of moles of Mg=Mass(g)/Molar Mass(g/mol)
look in your periodic table for the atomic weight of Mg plug it as the molar mass and you have the mass given.
Calculate the enthalpy change in KJ
q/1000/number of moles of Mg

Answer 2

Thanks a lot!
so the enthalpy would be the q value divided by 1000 divided by moles?

Answer 3

you are most welcome :D
yes q divided by 1000 and then divide it again by the number of moles of Mg

Answer 4

Ok I got it! thanks again!