Calculate the heat for the overall reaction: Mg(s) + 1/2O2 → MgO(s) given the heats of reaction below: Mg(s) + - Chemistry - Chemical Kinetics

Question

Calculate the heat for the overall reaction: Mg(s) + 1/2O2 →
MgO(s) given the heats of reaction below: Mg(s) + 2HCl(aq) →
MgCl2(aq) + H2(g) ∆H = –143 kJ MgO(s) + 2HCl(aq) →
MgCl2(aq) + H2O(g) ∆H = –216 kJ H2(g) + 1/2O2 →
H2O(l) ∆H = –285 kJ (A) –644 kJ (B) –212 kJ
(C) +644 kJ (D) –74 kJ (E) +74 kJ

Vartika Jain · Accepted Answer

Dear Student,

(i) Mg(s)  +  2HCl(aq)  →   MgCl2(aq)  +  H2(g)                 ∆Hi=-143 kJ(ii) MgO(s)  +  2HCl(aq)  →   MgCl2(aq)  +  H2O(g)          ∆Hii=-216 kJ(iii) H2(g) +  12O2(g)  →  H2O(l)                                            ∆Hiii=-285 kJThe required equation is,(iv)Mg(s) + 12O2(g) → MgO(s)                                     ∆H?The above equation can be obtained as, (iv)=[(i)-(ii)]+(iii)∆H=[∆Hi-∆Hii]+∆Hiii      =[-143-(-216)]+(-285)      =73-285      =-212 kJHence, correct answer is (B)