Respuesta :
The enthalpy of the reaction
Ca(s) + 1/2 O₂(g) + CO₂(g) → CaCO₃(s) is 813.4 kJ.
What is Hess's law of constant heat?
According to Hess's law of constant heat summation, the heat evolved or absorbed in a given chemical equation is the same whatever the process occurs in one step or in several steps .
According to given law, the chemical equation can be treated as ordinary algebraic expression and it can be added or subtracted to produce the required equation which means the enthalpy change of the complete reaction is the sum of the enthalpy changes of the intermediate reactions.
The given final reaction is,
Ca(s) + 1/2 O₂(g) + CO₂(g) → CaCO₃(s)
The intermediate balanced chemical reaction can be,
Ca(s) + 1/2 O₂(g) → CaO(s) ∆H°2 = 178.3kJ
CaCO₃(s) → CaO(s) + CO₂(g) ∆ H°1 = -635.1 kJ
Firstly we will go through the reversing of the reaction 2 and multiply equation 1 by 1 then adding both the equation, we obtained:
Ca(s) + 1/2 O₂(g) → CaO(s) ∆H°2 = 178.3kJ
CaO(s) + CO₂(g) → CaCO₃(s) ∆ H°1 = 635.1 kJ
The expression for final enthalpy is,
∆H = ∆H°1 + ∆H°2
∆H = 635.1 kJ + 178.3kJ
∆H = 813.4 kJ.
Thus, we calculated that the enthalpy of the reaction
Ca(s) + 1/2 O₂(g) + CO₂(g) → CaCO₃(s) is 813.4 kJ.
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