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Hess’s Law

Chemistry ⇒ Thermochemistry and Energetics

Hess’s Law starts at 11 and continues till grade 12. QuestionsToday has an evolving set of questions to continuously challenge students so that their knowledge grows in Hess’s Law. How you perform is determined by your score and the time you take. When you play a quiz, your answers are evaluated in concept instead of actual words and definitions used.
See sample questions for grade 11
Describe a situation where Hess’s Law would be necessary to determine the enthalpy change of a reaction.
Describe how you would use Hess’s Law to calculate the enthalpy change for the formation of methane from its elements.
Describe the relationship between Hess’s Law and the concept of state functions.
Describe the steps involved in using Hess’s Law to calculate the enthalpy change of a reaction.
Explain how Hess’s Law can be used to determine the enthalpy of combustion of a substance.
Explain why Hess’s Law is useful in thermochemistry.
Explain why it is important to specify the physical states of reactants and products when applying Hess’s Law.
Explain why the enthalpy change for a reaction is a state function.
Given the following data: (1) 2C(s) + O₂(g) → 2CO(g), ΔH = -221 kJ (2) 2CO(g) + O₂(g) → 2CO₂(g), ΔH = -566 kJ. Calculate the enthalpy change for 2C(s) + 2O₂(g) → 2CO₂(g).
Given the following data: (1) 2H₂(g) + O₂(g) → 2H₂O(l), ΔH = -572 kJ (2) 2H₂O(l) → 2H₂O(g), ΔH = +88 kJ. Calculate the enthalpy change for 2H₂(g) + O₂(g) → 2H₂O(g).
Given the following data: (1) C(s) + O₂(g) → CO₂(g), ΔH = -393.5 kJ (2) H₂(g) + ½O₂(g) → H₂O(l), ΔH = -285.8 kJ (3) CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(l), ΔH = -890.3 kJ. Calculate the enthalpy of formation of CH₄(g).
Given the following data: (1) N₂(g) + O₂(g) → 2NO(g), ΔH = +180 kJ (2) 2NO(g) + O₂(g) → 2NO₂(g), ΔH = -114 kJ. Calculate the enthalpy change for N₂(g) + 2O₂(g) → 2NO₂(g).
Given the following reactions: (1) C(s) + O₂(g) → CO₂(g), ΔH = -393.5 kJ (2) CO(g) + ½O₂(g) → CO₂(g), ΔH = -283.0 kJ. Calculate the enthalpy change for C(s) + ½O₂(g) → CO(g).
Given the following reactions: (1) CaCO₃(s) → CaO(s) + CO₂(g), ΔH = +178 kJ (2) CaO(s) + H₂O(l) → Ca(OH)₂(s), ΔH = -65 kJ (3) CaCO₃(s) + H₂O(l) → Ca(OH)₂(s) + CO₂(g), ΔH = ? Calculate ΔH for reaction (3).
Given the following reactions: (1) H₂(g) + ½O₂(g) → H₂O(l), ΔH = -286 kJ (2) H₂(g) + O₂(g) → H₂O₂(l), ΔH = -188 kJ. Calculate the enthalpy change for H₂O₂(l) → H₂O(l) + ½O₂(g).
Given the following reactions: (1) S(s) + O₂(g) → SO₂(g), ΔH = -297 kJ (2) 2SO₂(g) + O₂(g) → 2SO₃(g), ΔH = -198 kJ. Calculate the enthalpy change for 2S(s) + 3O₂(g) → 2SO₃(g).
If the enthalpy change for reaction A → B is +50 kJ and for B → C is -30 kJ, what is the enthalpy change for A → C?
State Hess’s Law.
A chemist wants to determine the enthalpy change for the reaction: 2SO2(g) + O2(g) → 2SO3(g). The following data are available: (1) S(s) + O2(g) → SO2(g), ΔH = -297 kJ (2) S(s) + 1.5O2(g) → SO3(g), ΔH = -395 kJ. Use Hess’s Law to calculate the enthalpy change for the target reaction.
A student wants to determine the enthalpy change for the reaction: C2H4(g) + H2(g) → C2H6(g). The following data are available: (1) C2H4(g) + 3O2(g) → 2CO2(g) + 2H2O(l), ΔH = -1411 kJ (2) C2H6(g) + 3.5O2(g) → 2CO2(g) + 3H2O(l), ΔH = -1555 kJ (3) H2(g) + 0.5O2(g) → H2O(l), ΔH = -286 kJ. Using Hess’s Law, calculate the enthalpy change for the target reaction.