As always n n OWL LonCapa assignments Lecture

As always… n n OWL Lon-Capa assignments Lecture videos Textbook n n Read Do text homework 1

Determining Hrxn n Since H = qp, determine the heat given off or required at constant pressure by measuring temperatures. This is termed calorimetry. Since energy is conserved, we can often determine Hrxn for one reaction given values of Hrxn for others. Uses the principle in Hess’s Law. Use standard enthalpies of formations for reactants and products (we have tables of these). 2

Schematic Diagram of Energy Changes 3

Clicker Question Given the following enthalpies of formation, determine the heat involved when 2. 1 mol of methane reacts with excess chlorine gas at constant pressure as follows: CH 4(g) + 4 Cl 2(g) CCl 4(l) + 4 HCl(g) ΔHf° (k. J/mol) – 75 – 135 – 92 a) b) c) d) e) 899 k. J are released 899 k. J are absorbed 1210 k. J are released 1210 k. J are absorbed 428 k. J are released 4

Clicker Question Given that ΔH°fusion for Fe(s) = 13. 6 k. J/mol and the following data: Fe 2 O 3(s) Al 2 O 3(s) ΔHf°(k. J/mol) – 826. 0 – 1676. 0 Determine ΔH°rxn (k. J) for thermite reaction (at constant temperature) as represented by the equation: Fe 2 O 3(s) + 2 Al(s) Al 2 O 3(s) + 2 Fe(l) a) – 822. 8 b) – 836. 4 c) – 850. 0 d) – 863. 6 e) – 877. 2 5

Chapter 9: Problem #117 This problem is an application of Hess’s law, although it may not be obvious upon reading it. 6