Practice Manipulating Equations And Enthalpy Changes (4.2.1) - Chapter 4: Energetics/Thermochemistry

Practice: Manipulating Equations and Enthalpy Changes

Lesson 4.2.1Energetics/Thermochemistry

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8 questions

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6 sample questions

Question 1.
What does Hess's Law state?
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Think of a journey taken by different routes.
Question 2.
What happens to the enthalpy change when we reverse a reaction?
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Review the direction of energy flow.
3Question 3.
What is Hess's Law?
- Energy change is always the same regardless of the path taken.
- Energy changes depend on the path taken.
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Recall the main principle of Hess's Law.
4Question 4.
True or False: When reversing a reaction, you must also reverse the sign of the enthalpy change.
- True
- False
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Think about how energy flows with direction.
Question 5.
Calculate the ΔH for this series of reactions involving CO2: C(s) + O2(g) → CO2(g) ΔH1 = -393.5 kJ, CO(g) + ½O2(g) → CO2(g) ΔH2 = -283.0 kJ. How does reversing reactions affect ΔH?
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Think carefully about how reversing a reaction changes the sign of the enthalpy.
Question 6.
Apply Hess's Law to find the total enthalpy change for this reaction: N2(g) + 3H2(g) → 2NH3(g). Use the given reactions: N2(g) + 2H2(g) → 2NH2(g) ΔH = -100 kJ, NH2 + H2 → NH3 ΔH = -50 kJ. What's ΔH?
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Manipulate the equations carefully; how do the signs play a role?

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