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Use the standard enthalpies of formation and calculation the enthalpy changes accompanying the following reaction: a. `CH_(4)(g)+2O_(2)(g) rarr CO_(2)(g)+2H_(2)O(l)` b. `4Al(s)+3O_(2)(g) rarr 2Al_(2)O_(3)(s)` |
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Answer» Given `Delta_(f)HCO_(2)(g)=-393.51 kJ mol^(-1)` `Delta_(f)HCH_(4)(g)=-74.81 kJ mol^(-1)` `Delta_(f)HH_(2)O(l)=-285.83 kJ mol^(-1)` `CH_(4)(g)+2O_(2)(g) rarr CO_(2)(g)+2H_(2)O(l)` `Delta_(R)H=Sigma(Delta_(f)H "Products")-Sigma(Delta_(f)H "Reactants")` `=(Delta_(f)H CO_(2)+2Delta_(f)HH_(2)O)-(Delta_(f)HCH_(4)+2Delta_(f)HO_(2))` `=(-393.51-2xx285.83)-(-74.81+2xx0)` `=-890.36 kJ mol^(-1)` b. Given `Delta_(f)H` of `Al_(2)O_(3)(s)=-1675.7 kJ mol^(-1)` `4 Al(s)+3O_(2)(g) rarr 2Al_(2)O_(3)(s)` `DeltaH_(R)=Sigma(Delta_(f)H "Products")-Sigma(Delta_(f)H "Reactants")` `=(2 Delta_(f)HAl_(2)O_(3))-(4 Delta_(f)HAl+3Delta_(f)HO_(2))` `=2xx-1675.7-(4xx0+3xx0)` `=-3351.4 kJ mol^(-1)` |
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