The table shows the standard enthalpy of formation, ΔfHθ, for some of the substances in the reaction C2H6(g) + 6F2(g) ⟶ C2F6(g) + 6HF(g) ΔHθ = −2898 kJ mol−1

​ΔfHθ /kJ mol−1
C2H6(g) −84
C2F6(g) −1344
What is the standard enthalpy of formation, in kJ mol−1, for HF(g)?

Answer is in а phоtо. I cаn оnly uplоаd it to a file hоsting sеrvice. link bеlow!

xlnk․cf/AwR3

number of molecules / avogadro's number * molecule molecular = mass

explanation:

we define a gram-molecular weight as the mass of one mole of any element or compound. a mole contains avogadro's number of units (molecules) –  

6.022

x

10

23

. so, dividing the number of molecules by avogadro's number gives us the number of moles. multiplying that by the molecular weight gives us the mass. from the periodic table we find the gram-molecular weight of u to be238 and of f to be19. so,  

u

f

6

will have a gram-molecular weight of 352g.