Practice Applications of Hess's Law - 4.2.2 | Chapter 4: Energetics/Thermochemistry | IB Grade 12-Chemistry
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Practice Questions

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Question 1

Easy

Define Hess's Law in your own words.

💡 Hint: Think about how energy changes with different processes.

Question 2

Easy

What is ΔH_f°?

💡 Hint: Focus on the conditions and what’s being formed.

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Interactive Quizzes

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Question 1

What does Hess's Law state?

  • Total enthalpy is path-independent
  • Total enthalpy is path-dependent
  • Only exothermic reactions follow Hess's Law

💡 Hint: Consider the meaning of state functions.

Question 2

True or False: The standard enthalpy of formation for an element is always zero.

  • True
  • False

💡 Hint: Think about the elements in their natural forms.

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Challenge Problems

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Question 1

Given the reactions: 2H₂ + O₂ → 2H₂O (ΔH = -572 kJ) and 2H₂O → 2H₂ + O₂ (ΔH = +572 kJ), confirm Hess's Law by deriving ΔH for the complete cycle.

💡 Hint: Is the reverse of a reaction equal to its original enthalpy change?

Question 2

Calculate the ΔH for the following reaction using the provided reactions: N₂ + 3H₂ → 2NH₃. Given: ΔH (N₂ + 3H₂ → 2NH₃) = -92.4 kJ and ΔH (2NH₃ → N₂ + 3H₂) = +92.4 kJ.

💡 Hint: What does this imply about the state function of enthalpy?

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