F10HW8-CH6

# F10HW8-CH6 - HOMEWORK WEEK 8 CHAPTER 6 6.6 An exothermic...

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HOMEWORK WEEK 8 CHAPTER 6 6.6 An exothermic reaction is a chemical reaction or a physical change in which heat is evolved (ΔH is negative). For example, burning one mol of methane, CH 4 (g), yields carbon dioxide, water, and 890.3 kJ of heat. An endothermic reaction is a chemical reaction or physical change in which heat is absorbed (ΔH is positive). For example, the reaction of one mol of barium hydroxide with ammonium nitrate absorbs 170.4 kJ of heat in order to form ammonia, water, and barium nitrate. 6.13 The heat capacity (C) of a substance is the quantity of heat needed to raise the temperature of the sample of substance one degree Celsius (or one Kelvin). The specific heat of a substance is the quantity of heat required to raise the temperature of one gram of a substance by one degree Celsius (or one Kelvin) at constant pressure. Units: J/g o C 6.20 The equation for the formation of H 2 S(g) is: H 2 (g) + 1/8S 8 (rhombic) H 2 S(g) (I would accept S(s) instead of 1/8 S 8 ) i.e. forming one mole of H 2 S from its elements in their normal states . [Note that the “enthalpy of formation” of H 2 S(g) is just the ΔH of the formation reaction.] 010. Using the fact that ΔH>0, the answer is c, endothermic, and the temperature of the resulting solution falls. 6.32 Let’s assume that ΔH of reaction equals -1000kJ, i.e. C 4 H 10 (g) + 13/2 O 2 (g) 4 CO 2 (g) + 5 H 2 O(g), ΔH = -1000kJ This gives us 4 separate pieces of information: When 1 mole of C 4 H 10 reacts completely, 1000kJ of heat are released. When 13/2 mole of O 2 react completely, 1000kJ of heat are released. When 4 mole of CO 2 are formed by this reaction, 1000kJ of heat are released. When 5 mole of H 2 O are formed by this reaction, 1000kJ of heat are released. The question concerns one mole of each species and we know that the ΔH or heat released is directly proportional to the moles involved. For instance for O 2 , Heat released by reaction of 1mol = 1 mol O 2 x 2 1000kJ 13/2 mol O = 154kJ Similarly when 1 mole of CO 2 is formed, we get 1000kJ/4mol = 250kJ Similarly when 1 mole of H 2 O is formed, we get 1000kJ/5mol = 200kJ Thus (b), 1 mol O 2 , yields the smallest amount of heat, because O

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## This note was uploaded on 02/20/2011 for the course CHEM 110 taught by Professor Dr.huston during the Spring '06 term at Pittsburgh.

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F10HW8-CH6 - HOMEWORK WEEK 8 CHAPTER 6 6.6 An exothermic...

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