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Chap 6 Sec 4

# Chap 6 Sec 4 - Section 4 Stoichiometry of Thermochemical...

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Chap 6 Sec 4 notes F09.doc 10/09 Page 1 Section 4 Stoichiometry of Thermochemical Reactions First – a few rules about what you can do with a thermochemical equation. KNOW HOW TO USE THESE. 1. You can reverse the equation and all that happens is the for H changes. H 2 + 1/2 O 2 -----> H 2 O(l) H = 285.8 kJ/mole H 2 O(l) -----> H 2 + 1/2 O 2 H = + 285.8 kJ/mole 2. You can multiply or divide the coefficients for a reaction as long to the H value. 2 [H 2 + 1/2 O 2 -----> H 2 O(l)] H = 2[ 285.8 kJ/mole] 2 H 2 + 1 O 2 -----> 2 H 2 O(l) H = 571.6 kJ/mole 3. The physical state of the elements or compounds makes a difference in the values. For us this will only become important in dealing with water. H 2 O(l) & H 2 O(g) both exist at room temperature. H 2 + 1/2 O 2 -----> H 2 O( g ) H = 241.8 kJ/mole (versus 285.8 for liquid) 4. The heat of a reaction is proportional to the amount of reaction, i.e.

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