Class work on Calorimetry January 11 and 12, 2011 Name 1. The number of calories needed to raise the temperature of 100 grams of water 10 degrees Celsius is the same as the number of calories needed to raise the temperature of 1,000 grams of water what amount? 2. A sample of water is heated from 10 C to 15 C by the addition of 30 calories of heat. What is the mass of the water? 3. The temperature of a sample of water increases from 30 degrees Celsius to 40 degrees Celsius as 100 calories of heat is added. What is the mass of the sample of water? 4. Heat is added to a substance at a constant rate and the temperature of the substance remains the same. What must be happening to the substance? 5. The difference between the boiling point and the freezing point of pure water in the Kelvin scale at standard pressure is. Show your work on this one. 6. When 100 calories of heat energy is added to 10 grams of water at 20 C, what is the final temperature of the water 7. When 5 grams of a substance is burned in a calorimeter 3 kilocalories of energy is released. What is the energy released per gram of substance?
8. What is the normal boiling point of water in Kelvin, Celsius and in Fahrenheit? 9. At which temperature would the molecules in a one gram sample of water have the lowest average kinetic energy? 10. How many kilocalories of heat energy are absorbed when 100 grams of water is heated from 20 degrees Celsius to 30 degrees Celsius? 11. The temperature of a sample of water in the liquid phase is changed from 15 degrees Celsius to 25 degrees Celsius by the addition of 500 calories. What is the mass of the water? 12. When 25 grams of water is cooled from 20 C to 10 C the number of calories of heat energy released is. 13. Given the equilibrium H 2 O (s) <======> H 2 O (l) at a pressure of 1 atmosphere. The temperature of the ice-water mixture must be 14. How many calories of heat energy are released when 50 grams of water are cooled from 70 C to 60 C? 15. Which of the following best describes exothermic chemical reactions? (1) They never release heat; (2) They always release heat; (3) They never occur spontaneously; (4) They always occur spontaneously. Explain you answer.
16. The number of calories needed to raise the temperature of 10 grams of water from 20 C to 30 C is. 17. Calculate the amount of energy necessary to heat a 2.5 g ice cube from 0 C to 23 C. 18. How much heat is required to raise the temperature of 100.0 g of Fe 2 O 3 from 5.0 C to 25.0 C? Specific heat for Fe 2 O 3 is 0.634 J /(g C). 19. Gold has a Specific Heat Capacity of 0.129 J /(g C). A gold ring that weighs 3.81 g is heated to 84.0 C and placed in 50.0 g of H 2 O at 22.1 C. What is the final temperature? 20. A 22.0 g piece of metal is heated to 100.0 C and placed in 75.0 g H 2 O at 25.0 C. If the final temperature of the metal and water is 27.8 C, what is the specific heat capacity of the metal in J /(g C)? (Assume no heat is lost/gained by the surroundings.) 21. An ice cube of unknown mass at 0 C is added to 265 g of H 2 O at 25.00 C in a calorimeter. If the final temperature of the resulting H 2 O is 21.70 C, what is the mass of the ice cube? The Heat of Fusion for the formation of ice (amount of energy needed to form ice from water) is 3.4x10 2 J/g. 22. 58.00g of a metal alloy is heated to 250 C then cooled by pouring into 200g of water at 25 C. When equilibrium is established both the metal and the water are at 65 C. What is the Specific heat capacity for the metal alloy? 23. A cup of coffee is at 100 C, and is too hot to drink. The best temperature to drink coffee at is 65 C. How much cold tap water at 16 C must be added to lower the coffee temperature to 65 C?
24. The specific heat capacity of glass is 0.75 J/(g C). A glass manufacturing company needs to cool a metric ton of glass from 850 C to 45 C. The plan is to put the glass in a cooling room on air cooled racks. The room temperature is 22 C and humans cannot work at temperatures above 40 C. The density of air is 0.130 g/ml and the specific heat of air 1 kj/(kg C). What is the volume of air that will be needed for this process? 25. The Specific Heat Capacity of iron is 0.4600 kj/(kg C). A 5.000 kg iron meteor falls into a small pond of only 6000.0 liters of water. The pond was originally at 22.00 C but the temperature rose to 95 C. What was the original temperature of the meteor?
Problems in Enthalpy January 11 and 12, 2011 1) For which of these is H f o not equal to zero? (A) Br2(l) (B) Fe(s) (C) I2(s) (D) O3(g) 2) Calculate the amount of energy expected from eating and digesting 50g of pure glucose, C 6 H 12 O 6. (You learned this reaction last year in biology) 3) The enthalpy change for which reaction represents the standard enthalpy of formation for hydrogen cyanide, HCN? a) H(g) + C(graphite) + N(g) (g) b) ½ H 2 (g) + C(graphite) + ½ N 2 (g) (g) c) HCN(g) H 2 (g) + C(graphite) + ½ N2(g) d) H 2 (g) + 2C(graphite) + N 2 (g) (g) 4) What is the standard enthalpy of formation of MgO(s) if 300.9 kj is evolved when 20.15 g of MgO(s) is formed by the combustion of magnesium under standard conditions? a) 601.8 kj mol 1 b) 300.9 kj mol 1 c) +300.9 kj mol 1 d) +601.8 kj mol 1 5) Consider this reaction. 2N 2 H 4 (l) + N 2 O 4 (l) 2 (g) + 4H 2 O(g) H = 1078 kj How much energy is released by this reaction during the formation of 140.0 g of N 2 (g)? a) 1078 kj b) 1797 kj c) 3234 kj d) 5390 kj 6) Use the information in the table to calculate the enthalpy of this reaction. C 2 H 6 (g) + 7/2O 2 (g) 2CO 2 (g) + 3H 2 O(l) Reaction H f o, kj mol 1 2C(s) + 3H 2 (g) C 2 H 6 (g) 84.7 2C(s) + O 2 (g) CO 2 (g) 393.5 H 2 (g) + ½ O 2 (g) 2O(l) 285.8 a) 764 kj b) 1560 kj c) 1664 kj d) 3120 kj 7) For the reaction PCl 3 (g) + Cl 2 (g) PCl 5 (g), H o = 86 kj. Under what temperatures is this reaction expected to be spontaneous? a) no temperatures
b) high temperatures only c) all temperatures d) low temperatures only Name 8) Calculate the amount of energy released when 0.100 mol of diborane, B 2 H 6, reacts with oxygen to produce solid B 2 O 3 and steam. Hf, (kj/mol) B2H6(g) 35 B2O3(s) -1272 H2O(l) -285 H2O(g) -241 a) 203 kj b) 216 kj c) 330 kj d) 343 kj 9) Given the thermochemical equations: Br2(l) + F2(g) 2BrF(g) H = -188 kj Br2(l) + 3F2(g) 2BrF3(g) H = -768 kj determine H for the reaction BrF(g) + F2(g) BrF3(g) H =? a) -956 kj b) -580 kj c) -478 kj d) -290 kj 10) The enthalpy change of which reaction corresponds to H f for Na 2 CO 3 (s) at 298 K? a) 2Na(s) + C(s) + 3 / 2 O2(g) Na 2 CO 3 (s) b) Na 2 O(s) + CO 2 (g) Na 2 CO 3 (s) c) 2Na + (aq) + CO 3 2- (aq) Na 2 CO 3 (s) d) 2Na + (aq) + 2OH (aq) + CO 2 (aq) Na 2 CO 3 (s) + H 2 O 11) Which applies to any endothermic reaction? a) H < 0 b) H > 0 c) G < 0 d) G > 0 12) When a bomb calorimeter is used to determine the heat of reaction, which property of the system under investigation is most likely to remain constant? a) number of molecules b) pressure c) temperature d) volume
13) H f (kj/mol) Cr 3+( aq) -143 Ni 2+ (aq) -54 For the reaction shown, which is closest to the value of H? 2Cr3+(aq) + 3Ni(s) 2Cr(s) + 3Ni2+(aq) Name 14) Which equation represents the reaction for the standard enthalpy of formation, ΔHf, for B 5 H 9 (g) at 298 K and 1 atm? a) 5B(s) + 9H(g) B 5 H 9 (g) b) 2B(s) + 3BH 3 (g) B 5 H 9 (g) c) 5 / 2 B 2 (g) + 9 / 2 H 2 (g) B 5 H 9 (g) d) 5 B(s) + 9 / 2 H2(g) B 5 H 9 (g) 15) C 2 H 6 (g) + 7 / 2 O 2 (g) 2CO 2 (g) + 3H 2 O(g) ΔH = 1427.7 kj If the enthalpy of vaporization for H 2 O(l) is 44.0 kj/mol, what is ΔH for this reaction if H 2 O(l) is formed instead of H2O(g)? a) 1295.7 kj (B) 1383.7 kj b) 1471.7 kj (D) 1559.7 kj 16) Calculate the change in enthalpy, ΔH, for the combustion of 11.2 L of hydrogen gas, measured at 0 C and 1 atm pressure, to form H 2 O(g). a) 60.5 kj b) 121 kj c) 484 kj d) 2710 kj 17) Given these reactions: A 2B ΔH = 40 kj B C ΔH = -50 kj 2C D ΔH = -20 kj Calculate ΔH for the reaction; D + A 4C. a) 100 kj b) 60 kj c) 40 kj d) 100 kj 18) The standard enthalpy of formation for NH3(g) is 46.1 kj/mol. Calculate ΔH for the reaction: 2NH3(g) N2(g) + 3H2(g)
a) 92.2 kj b) 46.1 kj c) 46.1 kj d) 92.2 kj Name 19) ΔH f (kj. mol -1 ) NaHCO 3 (s) 947.7 Na 2 CO 3 (s) 1130.9 H 2 O(g) 241.8 CO 2 (g) 393.5 Calculate the change in enthalpy (in kj per mole of CO2) for the decomposition of sodium hydrogen carbonate from the standard enthalpies of formation: 2 NaHCO 3 (s) Na 2 CO 3 (s) + H 2 O(g) + CO 2 (g) 20) For which reaction is ΔH rxn equal to ΔH f for CuSO 4 (s)? 21) ΔHf / kj mol 1 CuO 156.1 Cu 2 O 170.7 What is the value of ΔH (in kj) for this reaction? 4CuO(s) 2Cu 2 O(s) + O 2 (g) 22) Which statement is always true for an exothermic reaction? a) The enthalpy change is negative. b) The enthalpy change is positive. c) The reaction absorbs heat from the surroundings. d) The reaction is spontaneous. 23) NO(g) 2 (g) + 1/2O 2 (g) H 1 o 2NO(g) 2 O(g) + 1/2O 2 (g) H 2 o Which relationship is correct? a) ΔH 1 = ΔH 2 b) ΔH f for NO(g) = ΔH 1 c) ΔH f for N 2 O(g) = ΔH 2 d) ΔH f for N 2 O(g) = ΔH 2 2ΔH 1 24) When 2.74 g of Ba(s) reacts with O 2 (g) at 298 K and 1 atm to form BaO(s), 11,100 J of heat is released. What is ΔH f for BaO(s) in kj mol 1?
25) 25 grams of hydrogen is used to form water vapor from its elements. Water can then be further oxidized to form Hydrogen peroxide. Determine how much energy this will require or provide and the theoretical yield of Hydrogen peroxide.