THERMOCHEMISTRY PROBLEMS! WRITE A REACTION FOR PROBLEMS #1-8!
1. The DH for the reaction of propane (C3H8) burning is –2043 kJ. If I want to generate enough heat to cook an entire steak, which requires 255,000 kJ, how many grams of propane do I need?
2. Bombardier beetles produce a steam spray when they defend themselves. They produce the steam when hydrogen peroxide (H2O2) decomposes in their bodies into water and oxygen gas. The DH for this reaction is -190 kilojoules. How much heat is released in kilojoules when a beetle sprays 5 grams of water at its victim?
3. Acetic acid is the sour constituent of vinegar. In an experiment, 3.58 grams of acetic acid are burned. If 52.0 kJ of heat are evolved, then what is the DH in kilojoules of acetic acid burning?
4. A can of Campbell’s New England Clam Chowder contains 21 grams of carbohydrates per serving. Assuming that all 21 grams of carbohydrates are decomposed by the intestines into glucose (C6H12O6), calculate the number of FOOD CALORIES contained within one serving of soup. The DH for glucose combusting in the body is –2803 kilojoules per mole.
5. When a 1.82-gram sample of ethanol (CH3CH2OH) combusts surrounded by 220.0 grams of water in a calorimeter, the temperature rises from 22.00C to 75.00C. Calculate the DH for the reaction that took place in kilojoules.
6. When 23.5 grams of propane (C3H8) are burned, the temperature of a water calorimeter increases from 11.2 0C to 95.4 0C. The mass of the water is 3,104 grams. What is the DH in kilojoules, for propane burning?
7. When a 3.58-gram sample of potassium chlorate decomposes surrounded by 80 grams of water in a calorimeter, the temperature of the water rises from 20.50C to 24.40C. Calculate the DH for this chemical reaction, in kilocalories.
8. When a 43.5-gram sample of lithium nitrate dissolves in 62.3 grams of water in a calorimeter, the temperature drops from 27.20C to 13.20C. What is the DH for this process in kilojoules if the reaction is simply lithium nitrate dissolving into water to form lithium ion and nitrate ion?
9. Given the following reactions:
N2 (g) + O2 (g) ------> 2NO(g) DH = +180.7 kJ
2NO(g) + O2 (g) ------> 2NO2(g) DH = -113.1 kJ
2N2O(g) ------> 2N2(g) + O2 (g) DH = -163.2 kJ
Calculate the DH for dinitrogen monoxide reacting with nitrogen dioxide to form nitrogen monoxide.
10. Given the following thermodynamic data:
H2(g) + F2(g) ------> 2HF(g) DH = -537 kJ
C(g) + 2F2(g) ------> CF4(g) DH = -680 kJ
2C(s) + 2H2(g) ------> C2H4(g) DH = +52.3 kJ
Calculate the DH for the following reaction: C2H4(g) + 6F2(g) ------> 2 CF4(g) + 4HF(g)
11. Hydrogen cyanide is a highly poisonous, volatile liquid. It can be prepared by the reaction
CH4 (g) + NH3 (g) ------> HCN (g) + 3H2 (g)
What would be the heat released if 65.5 liters of ammonia were reacted at STP? Use the following thermodynamic data to calculate the DH0 for the reaction first!
N2 (g) + 3H2 (g) ------> 2NH3 (g) DH0 = -91.8 kJ
C (s) + 2H2g) ------> CH4 (g) DH0 = -74.9 kJ
H2 (g) + 2C(s) + N2 (g) ------> 2 HCN(g) DH0 = -270.3 kJ
12. Tungsten Carbide is a very hard material used to make cutting tools and rock drills. It is formed according to the following reaction:
W(s) + C(s) ------> WC(s)
What is the enthalpy change, or DH, for this reaction, given the following reactions?
2W(s) + 3O2(g) ------> 2WO3(s) DH = -1680 kJ
C(s) + O2 (g) ------> CO2 (g) DH = -393.5 kJ
2WC(s) + 5O2(g) ------> 2WO3(s) + 2CO2(g) DH = -2391.6 kJ
13. Sodium carbonate is used for manufacturing glass. It is obtained by heating sodium hydrogen carbonate, which also produces gaseous water and carbon dioxide. Calculate the standard enthalpy of reaction for this process.
14. Large quantities of ammonia are used to prepare nitric acid. The first step of this process involves reacting ammonia gas with oxygen gas to prepare nitrogen monoxide gas and water vapor. What is the standard enthalpy change, or DH, for this reaction?
15. Calculate the DH for the reaction of nitrogen dioxide gas with liquid water to make aqueous nitric acid and nitrogen monoxide under standard conditions.
16. Hydrogen gas is prepared by steam reforming, in which hydrocarbons are reacted with steam. For CH4,
CH4 (g) + H2O (g) ------> CO (g) + 3H2(g)
Calculate the enthalpy change DH0 for this reaction. Then, calculate the energy change when 55 grams of methane are reacted.
17. Calculate the heat released when 65.5 liters of hydrogen cyanide gas are released when aqueous hydrochloric acid was reacted with aqueous sodium cyanide at 250C and 760 mm Hg.
18. If 25.9 liters of gas are created at 250C and 760 Torr of pressure when solid ammonium nitrate is reacted with aqueous barium hydroxide, how many kJ of heat must have been absorbed?
19. If 750 mL of a 4M solution of sulfuric acid reacts with 150 grams of magnesium carbonate, how many kJ of heat would be released at 250C and 760 Torr?
20. Calcium oxide, or quicklime, is used in concrete. It is prepared from the decomposition of calcium carbonate (from limestone and seashells). Calculate the standard enthalpy of reaction for this process. Then, calculate the energy change if 55 liters of gas are evolved at 250C and 1 atm.
21. Calculate the heat released when 2.0 L of oxygen at 250C reacts with 6.0 L of hydrogen at the same pressure to form liquid water at a pressure of 760 mm Hg.
22. How much heat is produced when aqueous phosphoric acid is made for soda pop from 125 grams of a non-metal oxide solid with excess water at 250C at a pressure of 1 atm? Use the value for P4O10 and divide by 2 for the value for P2O5.
23. Kidney stones form when an individual drinks too much milk and soda. Milk contains aqueous calcium hydroxide, and soda contains aqueous phosphoric acid. How many kilojoules of heat are created in the body when 200 grams of aqueous calcium hydroxide are consumed as milk? Assume there is excess phosphoric acid in the body! Assume the reaction takes place at 250C and 1 atm.
24. The first Apollo mission that sent a three-man crew to the moon used a Saturn V rocket that 0burned kerosene in order to launch itself into space. Kerosene is C12H26. If 550,000 kilograms of kerosene were used in the first stage of the launch, which lasted only 2.5 minutes, how much heat was created if the DH for kerosene burning is –7513 kJ?
25. Iron is obtained from iron ore (ferric oxide) by reacting the ore with carbon monoxide gas. Carbon dioxide is also created. If 55 liters of carbon monoxide gas are stored at 800C and 120 kPa of pressure, and then the carbon monoxide is then brought to 250C and 1 atm of pressure so the reaction can be performed, how many kJ of heat would be released?