ENTHALPYASSIGNMENTs2 2022

ENTHALPY ASSIGNMENT #1 Knowledge /7 Inquiry /105 Applications /43 Communication /41 /196 Part A 1. Give the sign for ∆H for each of the following changes and state whether the reaction is endothermic or exothermic: ( K : / 4 ) a) Liquid bromine is converted into bromine vapour b) Carbon is burned in oxygen c) Water is decomposed into hydrogen and oxygen gas d) Liquid mercury freezes 2. Which of the following elements are in their standard states at 101.3 kPa and 25 o C ( K: /3 ) a) liquid nitrogen b) helium gas c) diamond d) iodine vapour e) ozone gas f) liquid bromine g) sodium metal 3. Consult the table and write thermochemical equations for the formation of 1 mol of the following substances at 25 o C ( C: /5 ) a) mercury (I) chloride solid b) Ca(OH) 2(s) c) Hg(g) d) C 2 H 5 OH (l) e) C 2 H 2(g) (acetylene) 4. The thermochemical equation for the combustion of carbon disulfide is CS 2(l) + 3O 2(g) → CO 2(g) + 2SO 2(g) + 1076.9 kJ (I: /4, C: /1 ) Calculate the enthalpy change when 25.0 g of CS 2 is burned? ( -353 kJ ) 5. Coke, which is obtained from the heat treatment of coal, consists of graphitic carbon. Estimate the number of kg of coke that will provide 500 000 kJ of energy when burned in an industrial furnace. Assume the major combustion product is CO 2 ( 15.2 kg ) ( I: /4, C: /2) 6. Given the following equation: 2C 3 H 6(g) + 9O 2(g) → 6CO 2(g) + 6H 2 O (l) + 4116.0 kJ Calculate the enthalpy change when 5.000 g of propene is combusted in an excess of oxygen gas. ( -244.9 kJ ) ( I: /6, C: /1)

7. Use Hess’s Law to calculate ∆H for: F 2(g) → 2F (g) ( I: /4) From the following data (1) HF (g) → H (g) + F (g) ∆H = 568 kJ (2) H 2(g) → 2H (g) ∆H = 436 kJ (3) ½ H 2(g) + ½ F 2(g) → HF (g) ∆H = -271 kJ ( 158 kJ ) 8. Use Hess’s Law to calculate ∆H for the reaction: C 2 H 2(g) + 2H 2(g) → C 2 H 6(g) from the following combustion data: ( I: /4 ) C 2 H 2(g) + 5/2O 2(g) → 2CO 2(g) + H 2 O (l) -1300 kJ H 2(g) + 1/2O 2(g) → H 2 O (l) -286 kJ C 2 H 6(g) + 7/2O 2(g) → 2CO 2(g) + 3H 2 O (l) -1560 kJ ( -312 kJ ) 9. pg. 264 question 11, 15 ( 336.6 kJ, 256 kJ) ( I: /8 ) 10. Write the combustion equations and use heats of formations to calculate the standard enthalpies of combustion for ( I: /6, C: /2 ) a) propane(C 3 H 8(g) ) b) octane(C 8 H 18(l) ) ( -2220 kJ ) (-5470.6 kJ ) 11. pg. 264 question 12, 16 ( I: /4, A: /12 C: /3 ) (- 466.5 kJ, -2657.0 kJ, -1427.80 kJ, -47.47 kJ/g, -462 kJ ) Bond Energy Values: C-C = 347 kJ, C-H = 414 kJ, H-H = 436 kJ, O=O = 498 kJ, C=O = 715 kJ, O-H = 464 kJ, N ≡N = 941 kJ 12. Using bond energies calculate the heat of combustion of butane (C 4 H 10(l) ) ( -1942 kJ ) ( I: /3, C: /1) 13. Given the following reaction: N 2(g) + 3H 2(g) →. 2NH 3(g) + 92.0 kJ Calculate the bond energy of the N-H bond. ( 390. kJ ) ( I: /4, C: /1 ) 14. How many joules of heat are required to raise the temperature of ( I: /6, C: /1 ) a) 15.0 g of Al given c sh = 0.900 J/g o C b) 1.50 mol of copper given c sh = 0.387 J/g o C from 20 to 30 o C ( 135 J, 369 J ) 15. When 1.50 g of morphine(C 17 H 19 O 3 N ∙ H 2 O) was burned in a bomb calorimeter,29.6 kJ of heat was given off. Calculate the constant volume heat of combustion of 1 mol of morphine. (- 5992 kJ ) ( I: /4, C: /1 )

23. 50.0 mL of 0.500 mol/L of copper (II) sulphate solution is mixed with 50.0 mL of 1.50 mol/L solution of sodium hydroxide in a coffee cup calorimeter. The temperature change for this reaction is 5.32 o C. Assume density and specific heat capacity same as water a) What is the enthalpy change for this reaction ( -88.8 kJ/mol ) b) Write the thermochemical equation Hints: coffee cup perfect insulator therefore not included in problem Find total volume, find mass using density, q = -(mc sh ∆T), write balanced equation, determine limiting reagent (set up statements since it is not 1:1), ∆H = q/n ( I: /11, C: /3 ) Part B - Making Connections 1. With increasing concerns about global warming and smog pollution, scientists have been looking at other sources of energy. One of these sources is hydrogen gas. Unfortunately, hydrogen gas is more difficult to store than liquids and solids. Calculate the volume of hydrogen at 20 o C and 101.325 kPa that is needed to produce the same amount of energy as the combustion of 1 L of octane, C 8 H 18 . The density of octane is 0.7025 g/mL and ∆H o f C 8 H 18(l) = -249.9 kJ . Make H 2 O (g) in the combustion of octane ( 3351 L ) ( A: /15, C: /4 ) Helpful hints: 1. Convert volume of octane to mass using density formula 2. Find moles of octane 3. Write the combustion reaction for octane and calculate ∆H using ∆H f 4. Solve for q = ∆H x n 5. q H2 = q octane 6. Write the combustion reaction of hydrogen gas to make gaseous water and calculate ∆H 7. Solve for n 8. Use ideal gas law to solve for the volume

2. Ethanol, C 2 H 5 OH and gasoline(octane) are both used as fuels in cars. If gasoline sells for $0.90/L, what price of ethanol have to be in order to provide the same amount of heat per dollar? The density of octane is 0.7025 g/mL and ∆H o f of ethanol is -277.6 kJ/mol and the density of ethanol is 0.7984 g/mL. Given ∆H o f C 8 H 18(l) = -249.9 kJ ( $0.63/L ) ( A: /14, C: /3 ) Helpful hints: 1. Convert volume of octane to mass using density formula 2. Find moles of octane 3. Write the combustion reaction for octane and calculate ∆H using ∆H f 4. Solve for q = ∆H x n 5. Repeat steps 1-4 for ethanol 6. Set up a proportion to solve for the price 3. What mass of pentane C 5 H 12(g) would have to be burned in an open system to heat 250.0 g of hot chocolate (c sh = 3.59 J/g o C) from 20.0 to 39.8 o C if the energy conversion is 45.0% efficient. Give ∆H f C5H12 = -146.44 kJ/mol. Make the H 2 O (g) for combustion of pentane. ( 0.841 g) ( A: /12, C: /3 ) Helpful Hints: 1. Find q output using q lost by rxn = -q gained by HC 2. Find q input using %efficiency formula 3. Write combustion reaction for pentane 4. Calculate ∆H using ∆H f 5. Find n = q/∆H 6. Find mass