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215
2Fe(s) + Al 2O 3 (s) ⎯⎯
→ 2Al(s) + Fe 2 O 3 (s)
3
2Al(s) + O 2 (g) ⎯⎯
→ Al 2O 3 (s)
2
3
2Fe(s) + O 2 (g) ⎯⎯
→ Fe 2 O 3 (s)
2
*22.
a)
;
ΔHº = +847.6 kJ
;
ΔHº = –1670 kJ
;
ΔHº = +847.6 kJ – 1670 kJ
Δ Hº = –822.4 kJ
Given the following equations and ΔHº values at 25ºC,
ΔHº = –911 kJ
Si(s) + O 2 (g) ⎯⎯
→ SiO 2 (s) ;
b)
2C(graphite) + O 2 (g) ⎯⎯
→ 2CO(g) ;
ΔHº = –221 kJ
c)
Si(s) + C(graphite) ⎯⎯
→ SiC(s) ;
ΔHº = –65.3 kJ
Calculate ΔHº for the following reaction, SiO 2 (s) + 3C(graphite) ⎯⎯
→ SiC(s) + 2CO(g) .
Given :
i)
Si(s) + O 2 (g) ⎯⎯
→ SiO 2 (s) ;
ΔHº = –911 kJ
ii)
2C(graphite) + O 2 (g) ⎯⎯
→ 2CO(g) ;
ΔHº = –221 kJ
iii) Si(s) + C(graphite) ⎯⎯
→ SiC(s) ;
To find :
ΔHº(reaction) = ?
Solution :
ΔHº = –65.3 kJ
→ SiC(s) + 2CO (g)
Required equation : SiO 2 (s) + 3C(graphite) ⎯⎯
Treatment : Reverse eq. (i) + eq. (ii) + eq. (iii)
∴
*23.
SiO 2 (s) ⎯⎯
→ Si(s) + O 2 (g) ;
ΔHº = +911 kJ
2C(graphite) + O 2 (g) ⎯⎯
→ 2CO(g) ;
ΔHº = –221 kJ
Si(s) + C(graphite) ⎯⎯
→ SiC(s) ;
ΔHº = –65.3 kJ
SiO 2 (s) + 3C(graphite) ⎯⎯
→ SiC(s) + 2CO(g) ;
ΔHº = +911 kJ –221 kJ –65.3 kJ
Δ Hº = +624.7 kJ
Given the following equations and ΔHº values at 25ºC,
a)
2H 3BO 3 (aq) ⎯⎯
→ B 2 O 3 (s) + 3H 2O(l ) ;
ΔHº = +14.4 kJ
b)
H 3BO 3 (aq) ⎯⎯
→ HBO 2 (aq) + H 2O(l ) ;
ΔHº = –0.02 kJ
c)
H 2 B 4 O 7 (s) ⎯⎯
→ 2B 2 O 3 (s) + H 2 O (l ) ;
ΔHº = 17.3 kJ calculate ΔHº for the following
reaction H 2 B 4 O 7 (s) + H 2O (l ) ⎯⎯
→ 4HBO 2 (aq)
Chapter - 3 Chemical Thermodynamics And Energetics
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