Hess's Law Worksheet
This worksheet covers Hess's Law, including calculations of enthalpy changes for chemical reactions using Hess's Law and understanding its applications.
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Hess's Law Worksheet
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Read each question carefully and answer to the best of your ability. Show all your work for calculation problems.
1. Hess's Law states that the enthalpy change of an overall reaction is equal to the sum of the enthalpy changes of individual steps. This is based on the principle of:
Conservation of mass
Conservation of energy
Le Chatelier's Principle
Avogadro's Law
2. Hess's Law is particularly useful for calculating enthalpy changes of reactions that are difficult or impossible to measure .
3. When a chemical equation is reversed, the sign of the enthalpy change (ΔH) must be .
4. Explain why Hess's Law is valid.
5. According to Hess's Law, the path taken from reactants to products affects the overall enthalpy change.
True
False
6. Calculate the enthalpy change (ΔH) for the reaction: C(s) + 2H2(g) → CH4(g)
Given the following reactions:
I. C(s) + O2(g) → CO2(g) ; ΔH = -393.5 kJ/mol
II. H2(g) + 1/2 O2(g) → H2O(l) ; ΔH = -285.8 kJ/mol
III. CH4(g) + 2O2(g) → CO2(g) + 2H2O(l) ; ΔH = -890.3 kJ/mol