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Blake Lecture 10-1-08 - CH 4 2O 2 = CH 2 2H 2 O-394-286 2...

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Blake 10-1-08 Chemistry How do you determine? Hess’s Law Heat of Formation Carliometry Ex 1: A system has 10.0 kJ of work done on it and releases 500.00 J of heat. What is the change in internal energy for the system? 1. -490 J 2. -510 J 3. +10500 J 4. -10500 J 5. -9500 J Ex 2: What is the heat of reaction for 2NOCl = N 2 + O 2 + Cl 2 Given NOCl = NO + 1/2Cl 2 H = 38.6 kJ 1/2N 2 + 1/2O 2 = NO H(NO) = 90.3 kJ ([-90.3 * 2] + [38.6 * 2]) = 103.4 kJ TOTAL = -103.4 kJ Ex 3: A system has 10.0 kJ of work done on it and releases 500.00 J of heat. The process is… 1. Exothermic 2. Endothermic 3. It can not be determined from the information given Heat of Formation The heat of a reaction equals the heat of formation of the products minus the heat of formation of the reactants. Watch states of reactants and products What is delta H for combustion of methane?
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Unformatted text preview: CH 4 + 2O 2 = CH 2 + 2H 2 O [(-394) + (-286 * 2)] – [(-75 * 1)] = -891 kJ Calorimetry • Run a reaction in an insulated container • Capture the heat given off by the reaction • Do Stoichiometry to report the heat in kJ/mole or kJ/gram Ex 4: The heat of combustion of benzoic acid -322.27 kJ/mole. If a 1.21 gram sample burns in a calorimeter that has a heat capacity of 1365 J/K and is filled with 1200 grams of water @ 23 degrees Celsius. What is the final temperature? Q = (m)(c)(delta T) C 6 H 5 COOH C 7 H 6 O 2 (122 GFM) (1.21 / 122) = (0.0099 moles * -322.37 kJ) = -32 kJ • +32 kJ (heat of water and calorimeter) • 32,000 J = 1365 (T f – 23 degrees Celsius) + (1200 * 4.18)(T f – 23 degrees Celsius)...
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