Problem 18
A magnesium ion, Mg2+, with a charge of 3.2⨉10-19 C and an oxide ion, O2-, with a charge of -3.2⨉10-19 C, are separated by a distance of 0.35 nm. How much work would be required to increase the separation of the two ions to an infinite distance?
- Identify the force present and explain whether work is being performed in the following cases: (a) You lift a book off the top of a desk. (b) Air is compressed in a bicycle pump.
Problem 19
- (a) Which of the following cannot leave or enter a closed system: heat, work, or matter? (b) Which cannot leave or enter an isolated system? (c) What do we call the part of the universe that is not part of the system?
Problem 21
Problem 22a
In a thermodynamic study, a scientist focuses on the properties of a solution in an apparatus as illustrated. A solution is continuously flowing into the apparatus at the top and out at the bottom, such that the amount of solution in the apparatus is constant with time. (a) Is the solution in the apparatus a closed system, open system, or isolated system?
Problem 22b
In a thermodynamic study, a scientist focuses on the properties of a solution in an apparatus as illustrated. A solution is continuously flowing into the apparatus at the top and out at the bottom, such that the amount of solution in the apparatus is constant with time. (b) If the inlet and outlet were closed, what type of system would it be
Problem 23a
(a) According to the first law of thermodynamics, what quantity is conserved?
Problem 23b
(b) What is meant by the internal energy of a system?
Problem 23c
(c) By what means can the internal energy of a closed system increase?
- (a) Write an equation that expresses the first law of thermodynamics in terms of heat and work. (b) Under what conditions will the quantities q and w be negative numbers?
Problem 24
Problem 25a
Calculate ΔE and determine whether the process is endothermic or exothermic for the following cases: (a) q = 0.763 kJ and w = -840 J.
Problem 25b
Calculate ΔE and determine whether the process is endothermic or exothermic for the following cases: (b) A system releases 66.1 kJ of heat to its surroundings while the surroundings do 44.0 kJ of work on the system.
Problem 26a,b
For the following processes, calculate the change in internal energy of the system and determine whether the process is endothermic or exothermic: (a) A balloon is cooled by removing 0.655 kJ of heat. It shrinks on cooling, and the atmosphere does 382 J of work on the balloon. (b) A 100.0-g bar of gold is heated from 25 °C to 50 °C during which it absorbs 322 J of heat. Assume the volume of the gold bar remains constant.
Problem 27a
A gas is confined to a cylinder fitted with a piston and an electrical heater, as shown here:
Suppose that current is supplied to the heater so that 100 J of energy is added. Consider two different situations. In case (1) the piston is allowed to move as the energy is added. In case (2) the piston is fixed so that it cannot move. (a) In which case does the gas have the higher temperature after addition of the electrical energy?
Problem 27b
A gas is confined to a cylinder fitted with a piston and an electrical heater, as shown here:
Suppose that current is supplied to the heater so that 100 J of energy is added. Consider two different situations. In case (1) the piston is allowed to move as the energy is added. In case (2) the piston is fixed so that it cannot move. (b) Identify the sign (positive, negative, or zero) of q and w in each case?
Problem 28a
Consider a system consisting of two oppositely charged spheres hanging by strings and separated by a distance r1, as shown in the accompanying illustration. Suppose they are separated to a larger distance r2, by moving them apart. (a) What change, if any, has occurred in the potential energy of the system?
Problem 29
(a) What is meant by the term state function? (b) Give an example of a quantity that is a state function and one that is not. (c) Is the volume of a system a state function? Why or why not?
- During a deep breath, our lungs expand about 2.0 L against an external pressure of 101.3 kPa. How much work is involved in this process (in J)?
Problem 31
- How much work (in J) is involved in a chemical reaction if the volume decreases from 33.6 L to 11.2 L against a constant pressure of 90.5 kPa?
Problem 32
- (c) For a given process at constant pressure, _x001F_H is negative. Is the process endothermic or exothermic?
Problem 33
- (a) Under what condition will the enthalpy change of a process equal the amount of heat transferred into or out of the system? (b) During a constant-pressure process, the system releases heat to the surroundings. Does the enthalpy of the system increase or decrease during the process? (c) In a constant-pressure process, _x001F_H = 0. What can you conclude about _x001F_E, q, and w?
Problem 34
- Assume that 2 moles of water are formed according to the following reaction at constant pressure (101.3 kPa) and constant temperature (298 K): 2 H2(g) + O2(g) → 2 H2O(l). (b) Calculate _x001F_E for the reaction using your answer to (a).
Problem 35
- Suppose that the gas-phase reaction 2 NO(g) + O2(g) → 2 NO2(g) were carried out in a constant-volume container at constant temperature. (a) Would the measured heat change represent _x001F_H or _x001F_E? (b) If there is a difference, which quantity is larger for this reaction? (c) Explain your answer to part (b).
Problem 36
Problem 38
A gas is confined to a cylinder under constant atmospheric pressure, as illustrated in Figure 5.4. When 0.49 kJ of heat is added to the gas, it expands and does 214 J of work on the surroundings. What are the values of H and E for this process?
Problem 39a
The complete combustion of methane, CH4(g), to form H2O(l) and CO2(g) at constant pressure releases 890 kJ of heat per mole of CH4. (a) Write a balanced thermochemical equation for this reaction.
Problem 39b
The complete combustion of methane, CH4(g), to form H2O(l) and CO2(g) at constant pressure releases 890 kJ of heat per mole of CH4. (b) Draw an enthalpy diagram for the reaction.
Problem 40a
The decomposition of sodium bicarbonate (baking soda), NaHCO3(s), into Na2CO3(s), H2O(l), and CO2(g) at constant pressure requires the addition of 85 kJ of heat per two moles of NaHCO3. (a) Write a balanced thermochemical equation for the reaction.
Problem 41a
Atomic hydrogen (H) is used in welding (AHW). The atoms recombine to hydrogen molecules with a large release of heat according to the following reaction: 2 H(g) → H2(g) (a) Using the thermodynamic data in Appendix C, calculate the enthalpy change for this reaction per mole of H2.
Problem 41b
Atomic hydrogen (H) is used in welding (AHW). The atoms recombine to hydrogen molecules with a large release of heat according to the following reaction: 2 H(g) → H2(g) (b) Which has the higher enthalpy under these conditions, 2 H(g) or H2(g)?
Problem 42a
Without referring to tables, predict which of the following has the higher enthalpy in each case: (a) 1 mol I2(s) or 1 mol I2(g) at the same temperature
Problem 42b
Without referring to tables, predict which of the following has the higher enthalpy in each case: (b) 2 mol of iodine atoms or 1 mol of I2
Ch.5 - Thermochemistry