Question

3) The first step in the industrial recovery of zinc from the zinc sulfide ore is roasting that is conversion of ZnS to ZnO by heating: 2ZNS(s)+ 302[g)2ZnO(s) + 2S02(g) AH--879 KJ/mol Calculate the heat evolved (in KJ) per gram of ZnS roasted. (3 points) 4) Given the thermochemical equations: (3 points) AHO-188 KJ/mol AH-768 KJ/mol Br2)+ F2g) 2BrF(g) Br2)+3F2(g) 2BrF3(g) Calculate the AHm for the reaction BrF(g)+ F2(g) BrF3(g)

Answer 1

3)

Molar mass of ZnS,

MM = 1*MM(Zn) + 1*MM(S)

= 1*65.38 + 1*32.07

= 97.45 g/mol

mass(ZnS)= 1 g

use:

number of mol of ZnS,

n = mass of ZnS/molar mass of ZnS

=(1 g)/(97.45 g/mol)

= 1.026*10^-2 mol

Since Δ H is negative, heat is released

when 2 mol of ZnS reacts, heat released = 879.0 KJ

So,

for 1.026*10^-2 mol of ZnS, heat released = 1.026*10^-2*879.0/2 KJ

= 4.51 KJ

This is heat evolved per gram of ZnS roasted

Answer: 4.51 KJ/g

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