G = H T S ( ) = ( ) ( )( )

Transcription

1 Chapter 8 Homework Problems Student Name TTh MW MW am mid pm Lab Section (circle one) CHEM 1A 1. Consider the following balanced thermochemical equation: Fe 2 O 3 (s) + 3 CO (g) 2 Fe (s) + 3 CO 2 (g) H Rxn = 24.8 kj (a) Is heat absorbed or released in the reaction (circle one)? (b) If the heat was written into the equation, would it appear on the reactant side or the product side of the equation (circle one)? (c) What is H Rxn for the reverse reaction? (d) What is H when g of CO reacts with excess Fe 2 O 3? 2. The reaction depicted to the right is exothermic: (a) Write a balanced equation for the reaction (red spheres represent A atoms and ivory spheres represent B atoms). (b) Label the sign (+ or ) of each variable in the equation below. If G depends on the temperature, enter a question mark (?). G = H T S ( ) = ( ) ( )( ) (c) Will the reaction be spontaneous at all temperatures, at low temperatures only, at high temperatures only, or at no temperatures (circle one)? 3. A reaction is exothermic, yet non-spontaneous under the current conditions. (a) What must the sign of S be? Fill in: S ( ) (b) Are the current conditions likely to be at high temperatures or low temperatures (circle one)? CHEM 1A Chapter 8 Page 1 of 6

2 4. Circle one for each of the following: (a) Is the heat capacity of a substance an intensive or an extensive property? (b) Is the specific heat of a substance an intensive or an extensive property? 5. A 30.5 g sample of an alloy at 93.0 C is placed into 50.0 g of water at 22.0 C in an insulated coffee cup with a heat capacity of 9.2 J/ C. If the final temperature of the system is 31.1 C, what is the specific heat capacity of the alloy? 6. A 45.2 g sample of iron and a 68.2 g sample of aluminum, both at 98.0 C, are placed into g of water at 23.2 C in an insulated coffee cup with a heat capacity of 8.7 J/ C. Calculate the final temperature of the system. C Fe = J/g C, C Al = J/g C CHEM 1A Chapter 8 Page 2 of 6

3 7. When 25.0 ml of M H 2 SO 4 is added to 25.0 ml of 1.00 M KOH (stoichiometric amounts) in a coffee cup calorimeter at C, the temperature rises to C. (a) Write a balanced chemical reaction for the acid-base neutralization occurring in the calorimeter. (b) Given the following assumptions, calculate H Rxn in kj/mol H 2 SO 4. Assume: all heat is transferred to the water, the solution volumes are additive, and the resulting solution has the same density and specific heat capacity as pure water Hint: H Rxn = q w # mol H 2 SO 4 8. Calculate the change in internal energy (in kj) when 89.5 g C 2 H 4 react with excess HCl at atm of pressure with a volume change of 71.5 L. C 2 H 4 (g) + HCl (g) C 2 H 5 Cl (g) H = 72.3 kj CHEM 1A Chapter 8 Page 3 of 6

4 9. Calculate H Rxn for given the following set of reactions: 2 NOCl (g) N 2 (g) + O 2 (g) + Cl 2 (g) ½ N 2 (g) + ½ O 2 (g) NO (g) NO (g) + ½ Cl 2 (g) NOCl (g) H = 90.3 kj H = 38.6 kj 10. Use Hess s law to calculate the standard heat of formation for aqueous nitric acid. (a) Write the balanced equation for the formation of 1 mole of nitric acid from elements in their natural state (you may need to use fractional coefficients for the reactants). (b) Complete and use the given reactions below: 3 NO 2 (g) + H 2 O (l) 2 HNO 3 (aq) + NO (g) H = kj 2 NO (g) + O 2 (g) 2 NO 2 (g) H = kj 4 NH 3 (g) + 5 O 2 (g) 4 NO (g) + 6 H 2 O (l) H = kj NH 3 (g) H = 46.1 kj H 2 O (l) H = kj CHEM 1A Chapter 8 Page 4 of 6

5 11. Calculate H for the reaction below using H your textbook. data from Table B1 of Appendix B in the back of SiO 2 (s) + 4 HF (g) SiF 4 (g) + 2 H 2 O (l) 12. The following equation is for the combustion of 1 mole of acetylene (C 2 H 2 ) in air: C 2 H 2 (g) + 5 / 2 O 2 (g) 2 CO 2 (g) + H 2 O (g) H = kj Calculate H of C 2 H 2 (g), given H of CO 2 (g) = kj/mol and H of H 2 O (g) = kj/mol CHEM 1A Chapter 8 Page 5 of 6

6 13. Although it is noble gas and inert under normal conditions, xenon can form compounds with highly electronegative elements like oxygen and fluorine. XeF 6 is formed by the direct reaction of the elements. (a) Write the balanced equation between xenon and fluorine to form 1 mole of XeF 6. (b) Calculate the Xe F bond energy in XeF 6, given that the heat of formation is 402 kj/mol, and the F F bond energy is 159 kj/mol. 14. Isopropyl (rubbing) alcohol, is prepared industrially by the process shown to the below. Calculate H using the average bond dissociation energies given in table to the right. Bond Bond Energy (kj/mol) C C 839 C=C 614 C C 347 C H 413 C=O (in CO 2 ) C O 358 O H 467 O=O 498 CHEM 1A Chapter 8 Page 6 of 6