when 10 grams of HI is completly decomposed of standard conditions 860 J of heat absorbed....?

Question

Calculate the ethalpy change in KJmol-1 of the following two reactions:
HI-----> 1/2H2 (g)+ 1/2 I 2 (g)
H2(g)+ I2-------> 2HI (g)

How do wrk this out, i can understand what's going on please tell how work this. It's not homework, i just practicing questions and can't do it. Thank you very much.

i gt the first part but can you explain how you work out second equation

Answer 1

Convert 10 grams HI into moles by dividing by the molar mass of HI. So, the decomposition of that many moles of HI has a Delta H of +860 J. To calculate DH for your first equation, just divide 860 J by the number of moles in 10 grams of HI. That will give you units of J/mol. Convert J to kJ and you're done.

For the second one, you can see that this equation is twice the first equation written backwards. So, take the DH for your first equation, multiply it by 2 and change the sign.