mid2a_f04

# mid2a_f04 - Please use the following constants and...

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Please use the following constants and conversions in the problems below as needed Planck’s constant : h = 6.626 × 10 -34 J-s Speed of Light : c = 3.00 × 10 8 m/s Rydberg Constant : R H = 1.10 × 10 7 m -1 Energy levels in hydrogen atom : E n = (-2.18 × 10 -18 J)(1/n 2 ) 1. [7 points] Which one of the following is an exothermic process? (a) ice melting (b) water evaporating (c) boiling soup (d) condensation of water vapor (e) Ammonium thiocyanate and barium hydroxide are mixed at 25 °C and the temperature drops 2. [7 points] The standard enthalpy of formation for ammonia, NH 3 (g), is H f ° = -46.2 kJ/mol. How much heat is released/absorbed when 1 mole of N 2 (g) is reacted with three moles of H 2 (g) to produce ammonia (at constant pressure)? (a) 46.2 kJ of heat is released (b) 46.2 kJ of heat is absorbed (c) 92.4 kJ of heat is released (d) 92.4 kJ of heat is absorbed (e) 23.1 kJ of heat is released 3. [7 points] Consider the combustion reaction between octane and oxygen in the cylinder of an automobile. The reaction generates CO 2 , H 2 O and heat, and at the same time the expanding gases push up the piston thereby powering the car. If the system is defined as the contents of the cylinder (not including the piston or the cylinder) which of the following statements is true for the system in this process? (a) The change in internal energy ( E) is negative (b) The change in internal energy ( E) is positive (c) The change in internal energy ( E) is zero (d) Not enough information is given to unambiguously determine the sign of E 4. [7 points] Which one of the following statements is true ? (a) Enthalpy is an intensive property (b) The enthalphy change for a reaction does not depend upon the state (solid, liquid, gas, aqueous) of the reactants and products (c) Enthalpy is a state function (d) Enthalpy is equal to the heat measured under conditions of constant volume (e) If the enthalpy change of a reaction is H rxn the reverse reaction will have an enthalpy change equal 1/ H rxn

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5. [7 points] Given the following standard enthalpies of formation: Br 2 (l) H f ° = 0 kJ/mol Br 2 (g) H f ° = 30.7 kJ/mol Br (g) H f ° = 112 kJ/mol Which of the following statements is false ?
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## mid2a_f04 - Please use the following constants and...

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