If C(s) + O2 (g) → CO2 (g);∆H = X, and CO (g) + 1/2 O2 (g) →CO2 (g); ∆H = Y,Then the heat of formation of CO(g) is
Correct answer: C. X - Y
- A. X + Y
- B. Y - X
- C. X - Y
- D. XY
Explanation
To find the heat of formation ΔH∘f of CO(g),we can use Hess's law,which states that the total enthalpy change for a reaction is same,regardless of the number of steps taken to get from the reactants to the products.In this case, we can use the given reactions to calculate ΔH∘f for CO(g). First, let's reverse the second equation and change its sign because we need to find the formation of CO(g) CO2(g)→CO(g)+1/2 O2(g); ΔH=−Y Now, let's add this equation to the given equation: C(s)+O2(g)→CO2(g); ΔH=X + CO2(g)→CO(g)+1/2O2(g); ΔH=−Y When we add these equations, the intermediate CO2(g) and 1/2O2(g) cancel out, leaving us with: C(s)→CO(g); ΔH=X−Y Therefore, the heat of formation CO(g) is X−Y.
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About Thermochemistry and Energetics of Chemical Reactions
Thermochemistry measures energy changes in chemical reactions and distinguishes exothermic from endothermic processes. Work covers systems, surroundings and state functions, internal energy, the first law of thermodynamics, enthalpy and Hess's law, including the sign conventions used when heat enters or leaves a system.
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