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CHE 1401 - Summer 2012 - Chapter 5 Homework 5 (Chapter 5: Thermochemistry) _______________________________________________________________________________ MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 1) A chemical reaction that absorbs heat from the surroundings is said to be __________ and has a __________ ΔH at constant pressure. A) endothermic, positive B) endothermic, negative C) exothermic, negative D) exothermic, positive E) exothermic, neutral 1) 2) The specific heat capacity of liquid water is 4.18 J/g-K. How many joules of heat are needed to raise the temperature of 5.00 g of water from 25.1°C to 65.3°C? A) 2.08 × 10-2 2) B) 54.4 C) 48.1 D) 840 E) 1.89 × 103 3) With reference to enthalpy changes, the term standard conditions means __________. 3) (a) P = 1 atm (b) some common temperature, usually 298 K (c) V = 1 L A) a only B) b only C) c only D) a and c E) a and b 4) Which one of the following is an exothermic process? A) water evaporating B) boiling soup C) ice melting D) condensation of water vapor E) Ammonium thiocyanate and barium hydroxide are mixed at 25°C: the temperature drops. 4) 5) The specific heat capacity of methane gas is 2.20 J/g-K. How many joules of heat are needed to raise the temperature of 5.00 g of methane from 36.0°C to 75.0°C? A) 0.0113 B) 429 C) 22.9 D) 88.6 E) 1221 5) 1 6) A 50.0-g sample of liquid water at 25.0 C is mixed with 29.0 g of water at 45.0°C. The final temperature of the water is ________°C. The specific heat capacity of liquid water is 4.18 J/g-K. A) 35.0 B) 102 C) 142 D) 32.3 E) 27.6 6) 7) The most abundant fossil fuel is __________. A) uranium B) petroleum C) hydrogen D) natural gas E) coal 7) 8) Which of the following is a statement of the first law of thermodynamics? A) Ek = 1 mν2 2 8) B) A negative ΔH corresponds to an exothermic process. C) ΔE = Efinal - Einitial D) Energy lost by the system must be gained by the surroundings. E) 1 cal = 4.184 J (exactly) 9) The British thermal unit (Btu) is commonly used in engineering applications. A Btu is defined as the amount of heat required to raise the temperature of 1 lb of water by 1°F. There are __________ joules in one Btu. 1 lb = 453.59 g; °C = (5/9)(°F - 32°); specific heat of H2O (l) = 4.18 J/g-K. A) 1054 B) 5.120 × 10-3 C) 60.29 D) 3415 E) Additional information is needed to complete the calculation. 10) For the species in the reaction below, ΔHf° is zero for __________. 2Co (s) + H2 (g) + 8PF3 (g) → 2HCo(PF3)4 (l) A) H2 (g) B) Co (s) C) HCo(PF3)4 (l) D) PF3 (g) E) both Co(s) and H2 (g) 2 9) 10) 11) The internal energy can be increased by __________. 11) (a) transferring heat from the surroundings to the system (b) transferring heat from the system to the surroundings (c) doing work on the system A) a and c B) b only C) c only D) b and c E) a only 12) Hydrogen peroxide decomposes to water and oxygen at constant pressure by the following reaction: 2H2O2 (l) → 2H2O (l) + O 2 (g) 12) △H = -196 kJ Calculate the value of q (kJ) in this exothermic reaction when 4.00 g of hydrogen peroxide decomposes at constant pressure? A) -11.5 B) -0.0217 C) -2.31 × 104 D) -23.1 E) 1.44 13) Objects can possess energy as __________. 13) (a) endothermic energy (b) potential energy (c) kinetic energy A) a only B) b only C) c only D) a and c E) b and c 14) For which one of the following reactions is ΔH°rxn equal to the heat of formation of the product? A) (1/2)N2 (g) + O2 (g) → NO 2 (g) B) 6C (s) + 6H (g) → C6H6 (l) C) N2 (g) + 3H2 (g) → 2NH3 (g) D) P (g) + 4H (g) + Br (g) → PH4Br (l) E) 12C (g) + 11H2 (g) + 11O (g) → C6H22O11 (g) 3 14) 15) The units of of specific heat are __________. A) J/mol B) g-K/J or g-°C/J C) K/J or °C/J D) J/g-K or J/g-°C E) J/K or J/°C 15) 16) The energy released by combustion of 1 g of a substance is called the __________ of the substance. A) specific heat B) nutritional calorie content C) heat capacity D) fuel value E) enthalpy 16) 17) For which one of the following reactions is the value of ΔH°rxn equal to ΔHf° 17) for the product? A) C2H2 (g) + H2 (g) → C2H4 (g) B) C (diamond) + O2 (g) → CO2 (g) C) 2Ca (s) + O2 (g) → 2CaO (s) D) 3Mg (s) + N2 (g) → Mg3N2 (s) E) 2C (graphite) + O2 (g) → 2CO (g) 18) The specific heat capacity of solid copper metal is 0.385 J/g-K. How many joules of heat are needed to raise the temperature of a 1.55-kg block of copper from 33.0°C to 77.5°C? A) 26.6 B) 2.66 × 104 C) 0.00558 D) 5.58 × 10-6 E) 1.79 × 105 4 18) 19) Which of the following is a statement of Hess's law? A) If a reaction is carried out in a series of steps, the ΔH for the reaction will equal the sum of the enthalpy changes for the individual steps. B) The ΔH for a process in the forward direction is equal to the ΔH for the process in the reverse direction. C) The ΔH for a process in the forward direction is equal in magnitude and opposite in sign to the ΔH for the process in the reverse direction. D) The ΔH of a reaction depends on the physical states of the reactants and products. E) If a reaction is carried out in a series of steps, the ΔH for the reaction will equal the product of the enthalpy changes for the individual steps. 19) 20) When a system __________, ΔE is always negative. A) absorbs heat and has work done on it B) gives off heat and has work done on it C) absorbs heat and does work D) gives off heat and does work E) none of the above is always negative. 20) 21) A __________ ΔH corresponds to an __________ process. A) negative, endothermic B) negative, exothermic C) positive, exothermic D) zero, exothermic E) zero, endothermic 21) 22) The internal energy of a system is always increased by __________. A) a volume compression B) adding heat to the system C) having the system do work on the surroundings D) withdrawing heat from the system E) adding heat to the system and having the system do work on the surroundings 22) 23) What is the enthalpy change (in kJ) of a chemical reaction that raises the temperature of 250.0 ml of solution having a density of 1.25 g/ml by 7.80 oC? (The specific heat of the solution is 3.74 joules/gram-K.) A) -7.43 B) -12.51 C) 8.20 D) 6.51 E) -9.12 23) 5 24) The specific heat capacity of liquid mercury is 0.14 J/g-K. How many joules of heat are needed to raise the temperature of 5.00 g of mercury from 15.0°C to 36.5°C? A) 1.7 B) 0.0013 C) 15 D) 7.7 × 102 E) 36 24) 25) In the reaction below, ΔHf° is zero for __________. 25) Ni (s) + 2CO (g) + 2PF3 (g) → Ni(CO) 2(PF3)2 (l) A) PF3 (g) B) Ni (s) C) Ni(CO) 2(PF3)2 (l) D) CO (g) E) both CO (g) and PF3 (g) 26) Of the following, which one is a state function? A) H B) heat C) w D) q E) none of the above 26) 27) Which one of the following statements is true? A) The enthalpy change of a reaction is the reciprocal of the ΔH of the reverse reaction. B) Enthalpy is an intensive property. C) Enthalpy is a state function. D) The enthalphy change for a reaction is independent of the state of the reactants and products. E) H is the value of q measured under conditions of constant volume. 27) 28) Under what condition(s) is the enthalpy change of a process equal to the amount of heat transferred into or out of the system? 28) (a) temperature is constant (b) pressure is constant (c) volume is constant A) a only B) b only C) c only 6 D) a and b E) b and c 29) A 6.50-g sample of copper metal at 25.0°C is heated by the addition of 84.0 J of energy. The final temperature of the copper is ________°C. The specific heat capacity of liquid water is 0.38 J/g-K. A) 34.0 B) 59.0 C) 29.9 D) 9.0 E) 25.0 29) 30) For a given process at constant pressure, ΔH is negative. This means that the process is __________. A) equithermic B) energy C) endothermic D) exothermic E) a state function 30) 31) Which one of the choices below is not considered a fossil fuel? A) natural gas B) hydrogen C) crude oil D) anthracite coal E) petroleum 31) 32) For which one of the following reactions is the value of ΔH°rxn equal to ΔH°f for the product? A) H2 (g) + 1/2 O2 (g) → H2O (l) B) 2 C (s, graphite) + 2 H2 (g) → C2H4 (g) 32) C) H2 (g) + O2 (g) → H2O 2 (l) D) 1/2 N2 (g) + O2 (g) → NO2 (g) E) all of the above 33) The units of of heat capacity are __________. A) g-K/J or g-°C/J B) J/mol C) J/K or J/°C D) K/J or °C/J E) J/g-K or J/g-°C 7 33) 34) The reaction 4Al (s) + 3O2 (g) → 2Al2O3 (s) 34) ΔH° = -3351 kJ is __________, and therefore heat is __________ by the reaction. A) exothermic, released B) endothermic, absorbed C) endothermic, released D) exothermic, absorbed E) thermoneutral, neither released nor absorbed 35) For which one of the following equations is ΔH°rxn equal to ΔHf° for the product? A) N2 (g) + O3 (g) → N2O 3 (g) B) CH4 (g) + 2Cl2 (g) → CH2Cl2 (l) + 2HCl (g) C) C (diamond) + O2 (g) → CO2 (g) D) 2CO (g) + O2 (g) → 2CO2 (g) E) Xe (g) + 2F2 (g) → XeF4 (g) 35) 36) At what velocity (m/s) must a 20.0 g object be moving in order to possess a kinetic energy of 1.00 J? A) 50.0 B) 1.00 × 103 C) 1.00 D) 100 × 102 E) 10.0 36) 37) Of the substances below, the highest fuel value is obtained from __________. A) natural gas B) wood C) hydrogen D) bituminous coal E) charcoal 37) 8 38) The combustion of titanium with oxygen produces titanium dioxide: 38) Ti (s) + O2 (g) → TiO2 (s) When 0.721 g of titanium is combusted in a bomb calorimeter, the temperature of the calorimeter increases from 25.00°C to 53.80°C. In a separate experiment, the heat capacity of the calorimeter is measured to be 9.84 kJ/K. The heat of reaction for the combustion of a mole of Ti in this calorimeter is __________ kJ/mol. A) 2.67 B) 4.98 C) -1.49 × 104 D) -0.154 E) -311 39) Which one of the following conditions would always result in an increase in the internal energy of a system? A) The system loses heat and does work on the surroundings. B) The system gains heat and has work done on it by the surroundings. C) The system gains heat and does work on the surroundings. D) The system loses heat and has work done on it by the surroundings. E) None of the above is correct. 39) 40) For which one of the following reactions is the value of ΔH°rxn equal to ΔH°f for the product? A) 2 H2 (g) + O2 (g) → 2 H2O (l) 40) B) 2 H2 (g) + O2 (g) → 2 H2O (g) C) N2 (g) + O2 (g) → 2 NO (g) D) H2O (l) + 1/2 O2 (g) → H2O2 (l) E) 2 C (s, graphite) + 2 H2 (g) → C2H4 (g) 9