<p>Honors Chemistry</p><p>Chapter 10 – Hess’s Law & Heats of Formation Practice</p><p>1. Hess’s law of heat summation: ______</p><p>2. When the reverse of a chemical reaction is written, what happens to the sign of ΔH? Why?</p><p>3. Calculate the enthalpy change, ΔH (in kJ) for the reaction: BaO (s) + H2SO4 (aq)  BaSO4 (s) + H2O (l) Use the following data: SO3 (g) + H2O (l)  H2SO4 (aq) ΔH = -78.2 kJ BaO (s) + SO3 (g)  BaSO4 (s) ΔH = -213.4 kJ</p><p>4. The following equation shows the combustion of ethane. 2C2H6 (g) + 7O2 (g)  4CO2 (g) + 6H2O (l) Use Hess’s law and following data to calculate the enthalpy change. C2H4 (g) + 3O2 (g)  2CO2 (g) + 2H2O (g) ΔH = -1323 kJ C2H4 (g) + H2 (g)  C2H6 (g) ΔH = -137 kJ H2 (g) + ½ O2 (g)  H2O (g) ΔH = -242 kJ</p><p>5. Calculate the enthalpy change, ΔH (in kJ) for the reaction: C (s) + 2H2 (g)  CH4 (g) Use the following data: C (s) + O2 (g)  CO2 (g) ΔH = -393.5 kJ H2 (g) + ½ O2 (g)  H2O (l) ΔH = -285.8 kJ CH4 (g) + 2O2 (g)  CO2 (g) + 2H2O (l) ΔH = -890.3 kJ</p><p>6. Calculate the standard molar enthalpy of formation, ΔHf˚, for the following using table A.6 on page 787. a) H2 (g) + ½ O2 (g)  H2O (l)</p><p> b) C (s) + 2H2 (g)  CH4 (g)</p><p> c) 2Al (s) + 3/2 O2 (g)  Al2O3 (s) d) ½ N2 (g) + 3/2 H2 (g)  NH3 (g)</p><p>7. What is the final temperature of 250.0 mL of water whose initial temperature is 25.0˚C if 80.0 g of aluminum initially at 70˚C is dropped into the water? The specific heat of aluminum is 0.215 cal/g˚C</p><p>8. A piece of unknown metal with a mass of 23.8 g is heated to 100.0˚C and dropped into 50 mL of water at 24.0˚C. The final temperature of the system is 32.5˚C. What is the specific heat of the metal?</p><p>9. You can find the amount of heat evolved in the combustion of carbon by carrying out the reaction in a combustion calorimeter. You burn 0.300 g of carbon (graphite) in excess of O2 (g) to give CO2 (g). C (graphite) + O2 (g)  CO2 (g) The temperature of the calorimeter, which contains 775 g of water, increases from 25˚C to 27.38˚C. What quantity of heat is evolved per mole of carbon?</p><p>10. You burn 1.5 g of benzoic acid, C7H6O2 (aq), in a combustion calorimeter and find that the temperature of the calorimeter increases from 22.5˚C to 31.69˚C. The calorimeter contains 775 g of water. Calculate the molar heat of combustion for one mole of benzoic acid. 2C7H6O2 (aq) + 15O2 (g)  14CO2 (g) + 6H2O (g)</p><p>11. Calculate the heat energy required to raise the temperature of 4.5 g of water from -8˚C to 105.7˚C. Draw a diagram to show phase changes. Cice = 2.05 J/g˚C Csteam = 2.05 J/g˚C ΔHfus = 6.01 kJ/mol ΔHvap = 40.7 kJ/mol</p><p>12. How much heat energy is released when 12.8 g of barium oxide react with excess sulfur trioxide? BaO (s) + SO3 (g)  BaSO4 (s) ΔH = -213.4 kJ</p>