4. Energetics

Hess Law — Quiz

Test your understanding of hess law with 5 practice questions.

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Practice Questions

Question 1

Which property of enthalpy ensures that Hess’s law can be applied to calculate reaction enthalpies?

Question 2

Which of the following substances has a standard enthalpy of formation ΔHf° equal to zero at 1 bar and 298 K?

Question 3

Calculate the enthalpy change ΔH° for the reaction C₂H₂(g) + H₂(g) → C₂H₄(g) using standard enthalpies of formation ΔHf°(C₂H₂)=+227 kJ/mol, ΔHf°(C₂H₄)=+52 kJ/mol, ΔHf°(H₂)=0 kJ/mol.

Question 4

Using the combustion reaction CH₃COOH(l)+2O₂(g)→2CO₂(g)+2H₂O(l) with ΔH°combustion=−875.5 kJ, and standard enthalpies of formation ΔHf°(CO₂)=−393.5 kJ/mol and ΔHf°(H₂O)=−285.8 kJ/mol, calculate ΔHf° of CH₃COOH(l).

Question 5

Given the thermochemical steps A→B ΔH₁=+100 kJ, B→C ΔH₂=−40 kJ, and 2C→D ΔH₃=+80 kJ, what is ΔH° for the reaction 2A→D?