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```215
2Fe(s) + Al 2O 3 (s) â¯â¯
â 2Al(s) + Fe 2 O 3 (s)
3
2Al(s) + O 2 (g) â¯â¯
â Al 2O 3 (s)
2
3
2Fe(s) + O 2 (g) â¯â¯
â Fe 2 O 3 (s)
2
*22.
a)
;
ÎHÂº = +847.6 kJ
;
ÎHÂº = â1670 kJ
;
ÎHÂº = +847.6 kJ â 1670 kJ
Î HÂº = â822.4 kJ
Given the following equations and ÎHÂº values at 25ÂºC,
ÎHÂº = â911 kJ
Si(s) + O 2 (g) â¯â¯
â SiO 2 (s) ;
b)
2C(graphite) + O 2 (g) â¯â¯
â 2CO(g) ;
ÎHÂº = â221 kJ
c)
Si(s) + C(graphite) â¯â¯
â SiC(s) ;
ÎHÂº = â65.3 kJ
Calculate ÎHÂº for the following reaction, SiO 2 (s) + 3C(graphite) â¯â¯
â SiC(s) + 2CO(g) .
Given :
i)
Si(s) + O 2 (g) â¯â¯
â SiO 2 (s) ;
ÎHÂº = â911 kJ
ii)
2C(graphite) + O 2 (g) â¯â¯
â 2CO(g) ;
ÎHÂº = â221 kJ
iii) Si(s) + C(graphite) â¯â¯
â SiC(s) ;
To find :
ÎHÂº(reaction) = ?
Solution :
ÎHÂº = â65.3 kJ
â SiC(s) + 2CO (g)
Required equation : SiO 2 (s) + 3C(graphite) â¯â¯
Treatment : Reverse eq. (i) + eq. (ii) + eq. (iii)
â´
*23.
SiO 2 (s) â¯â¯
â Si(s) + O 2 (g) ;
ÎHÂº = +911 kJ
2C(graphite) + O 2 (g) â¯â¯
â 2CO(g) ;
ÎHÂº = â221 kJ
Si(s) + C(graphite) â¯â¯
â SiC(s) ;
ÎHÂº = â65.3 kJ
SiO 2 (s) + 3C(graphite) â¯â¯
â SiC(s) + 2CO(g) ;
ÎHÂº = +911 kJ â221 kJ â65.3 kJ
Î HÂº = +624.7 kJ
Given the following equations and ÎHÂº values at 25ÂºC,
a)
2H 3BO 3 (aq) â¯â¯
â B 2 O 3 (s) + 3H 2O(l ) ;
ÎHÂº = +14.4 kJ
b)
H 3BO 3 (aq) â¯â¯
â HBO 2 (aq) + H 2O(l ) ;
ÎHÂº = â0.02 kJ
c)
H 2 B 4 O 7 (s) â¯â¯
â 2B 2 O 3 (s) + H 2 O (l ) ;
ÎHÂº = 17.3 kJ calculate ÎHÂº for the following
reaction H 2 B 4 O 7 (s) + H 2O (l ) â¯â¯
â 4HBO 2 (aq)
Chapter - 3 Chemical Thermodynamics And Energetics
```
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