15.3 Hess Law

15.3 Hess Law - Using the list of reactions below and...

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Dr. Paul Moses 15.3 Hess’s Law Concept Worksheet The basis of Hess’s law is that if you can add two reactions to get a third reaction, then the energy of the third reaction with be the sum of the energies of the two reactions you add. In the process of doing this, you may need to reverse one of the reactions. When you reverse a reaction, you change the sign on ΔH. You may also need to multiply a reaction by a factor to alter the coefficients to match that of the desired final reaction. When you use a factor for the reaction, ΔH gets multiplied by the same factor. Practice Problems:
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Unformatted text preview: Using the list of reactions below and associated enthalpies, determine the enthalpy of these reactions: a. 2 CO (g) + O 2(g) 2 CO 2(g) b. Fe 2 O 3(s) + 3 CO (g) 2 Fe (s) + 3 CO 2(g) c. CaO (s) + CO (g) Ca (s) + CO 2(g) d. CaO (s) + H 2(g) Ca (s) + H 2 O (g) List of known reactions: ΔH C (s) + O 2(g) CO 2(g)-394 KJ 2 C (s) + O 2(g) 2 CO (g)-220KJ 4 Fe (s) + 3 O 2(g) 2 Fe 2 O 3(s)-1648 KJ CaO (s) + CO 2(g) CaCO 3(s)-177 KJ 2 Ca (s) + O 2(g) 2 CaO (s)-1270 KJ 2 H 2(g) + O 2(g) 2 H 2 O (g)-483 KJ Answers: a.-568 KJ b.-28 KJ c. +351 KJ d. +393 KJ...
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