CHAPTER 17: Temperature, Thermal Expansion, and the Ideal Gas Law Responses to Questions. Properties of materials that could be exploited in making a thermometer include: a. thermal expansion, both linear and volume b. the proportionality between temperature and pressure (for an ideal gas when volume is held constant) c. temperature dependence of resistivity d. frequency of emitted radiation from a heated object (blackbody radiation curve). (Note: resistivity and blackbody radiation are defined in olume II.) 5. No. We can only infer that the temperature of C is different from that of A and B. We cannot infer anything about the relationship of the temperatures of A and B. 9. Lower. Mercury has a larger coefficient of volume expansion than lead. When the temperature rises, mercury will expand more than lead. The density of mercury will decrease more than the density of lead will decrease, and so the lead will need to displace more mercury in order to balance its weight. 11. If water is added quickly to an overheated engine, it comes into contact with the very hot metal parts of the engine. Some areas of the metal parts will cool off very rapidly; others will not. Some of the water will quickly turn to steam and will expand rapidly. The net result can be a cracked engine block or radiator, due to the thermal stress, and/or the emission of high temperature steam from the radiator. Water should always be added slowly, with the engine running. The water will mix with the hotter water already in the system, and will circulate through the engine, gradually cooling all parts at about the same rate. 15. Slow. On a hot day, the brass rod holding the pendulum will expand and lengthen, increasing the length and therefore the period of the pendulum, causing the clock to run slow.
16. Soda is essentially water, and water (unlike most other substances) expands when it freezes. If the can is full while the soda is liquid, then as the soda freezes and expands, it will push on the inside surfaces of the can and the ends will bulge out. 17. The coefficient of volume expansion is much greater for alcohol than for mercury. A given temperature change will therefore result in a greater change in volume for alcohol than for mercury. This means that smaller temperature changes can be measured with an alcohol thermometer. Solutions to Problems 6. Assume that the temperature and the length are linearly related. The change in temperature per unit length change is as follows. T 100.0C 0.0C 9.970C cm l 1.85 cm 11.8 cm Then the temperature corresponding to length L is T 0.0C 11.8 cm9.970c cm (a) T 18.70 cm 0.0 C 18.70 cm 11.8 cm 9.970C cm 68.6C (b) T 14.60 cm 0.0 C 14.60 cm 11.8 cm 9.970C cm 7.7C l l. 7. Take the 00 m height to be the height in January. Then the increase in the height of the tower is given by Eq. 17-1a. 6 l l T 1 10 C 00 m 5C C 0.08 m 0 10. The increase in length of the rod is given by Eq. 17-1a. l l 0.010 l l T T T T i 5C+ 551.C 550C 19 10 C 0 f 6 l l 0 0 11. The density at 4 o M 1.00 10 kg C is. When the water is warmed, the mass will stay the 1.00m same, but the volume will increase according to Eq. 17-.
T 10 10 C 1.00 m 94C 4C 1.89 10 m 0 6 The density at the higher temperature is M 1.00 10 kg 1.00 m 1.89 10 m 981kg m 14. Assume that each dimension of the plate changes according to Eq. 17-1a. 0 A A A l l w w l w l w l w wl l w l w l w wl l w Neglect the very small quantity l w. l A l w wl l wt w T l wt 15. The change in volume of the aluminum is given by the volume expansion formula, Eq. 17-. 4 T 6 8.75 cm 75 10 C 180 C 0 C.9 cm 0 0. (a) When a substance changes temperature, its volume will change by an amount given by Eq. 17-. This causes the density to change. T. M M M M M M M 1 f 1 T 1 T 0 0 0 0 0 0 0 1 1 T T 1 T 1 T 1 T If we assume that T = 1, then the denominator is approximately 1, so (b) The fractional change in density is T T 87 10 C55C 5C 6.96 10 This is a 0.70% increase. 6
. (a) The original surface area of the sphere is given by A 4 r. The radius will expand with temperature according to Eq. 17-1b, r r T. The final surface area is 1, and so the change in area is A A A. A 4 r A A A 4 r 1 T 4 r 4 r 1 T 1 1 4 r 1 T T 1 4 r T 1 T If the temperature change is not large, 1 T = 1, and so A 8 r T (b) Evaluate the above expression for the solid iron sphere. A 8 r T 8 60.0 10 m 1 10 C 75C 15C.8 10 m 6 5. The thermal stress must compensate for the thermal expansion. E is Young s modulus for the aluminum. Stress F A ET 510 C 70 10 N m 5C 18C.0 10 N m 6 9 7 1. Assume the gas is ideal. Since the amount of gas is constant, the value of P T is constant. P P P T 1.00 atm 7 8.0 K 1 1 1 1.80 m 1.5m T T P T.0 atm 7 K 1 1. Assume the nitrogen is an ideal gas. From Example 17-10, the volume of one mole of nitrogen gas at STP is.4 10 m. The mass of one mole of nitrogen, with a molecular mass of 8.0 u, is 8.0 grams. Use these values to calculate the density of the oxygen gas. M 8.0 10 kg.4 10 m 1.5kg m
7. (a) Assume the nitrogen is an ideal gas. The number of moles of nitrogen is found from the atomic weight, and then the ideal gas law is used to calculate the volume of the gas. n 1 mole N 8.5 kg 1017 mol 8.0110 kg 1017 mol 8.14 J molgk 7 K nrt P nrt.79 m.8 m 5 P 1.01 10 Pa (b) Hold the volume and temperature constant, and again use the ideal gas law. 1 mole N n 8.5 kg 5.0 kg 1910 mol 8.0110 kg P nrt 1910 mol 8.14 J molgk 7 K nrt P.79 m 5 1.90 10 Pa 1.88atm 41. We assume that the gas is ideal, that the amount of gas is constant, and that the volume of the gas is constant. P P P 1.00atm T T 1 7.15 0.0K 586.K 1.15 C 1 C T T P 1.00atm 1 1 4. Assume that the air is an ideal gas. The pressure and volume are held constant. From the ideal gas law, the value of P R n T nt is held constant. n T 1 n T 1 1 n T 1 Thus 8.0% must be removed. 7 8 K 11 1.080 7 15 K 88 48. From the ideal gas equation, we have P nrt and P nrt, since the amount of gas is 1 1 1 constant. Use these relationships along with the given conditions to find the original pressure and temperature.
; 450 Pa 450 Pa 9.0 K P nrt P nrt P P nrt nrt nr T T 1 1 1 1 1 1 1 P P nr T T P nr 1 1 1 1 1 1 nr P 9.0 K 450 Pa 4.0 mol8.14 J molgk 9.0 K 0.018m 450 Pa 1 1 5 5 1.57 10 Pa 1.5 10 Pa 5 1.57 10 Pa0.00 m 4.0 mol8.14 J molgk 0.00 m P 1 1 T T 9.4 K 181C 1 1 nr 5. We assume that the water is at 4 o C so that its density is 1000kg m. 10 m 1000 kg 1 mol 1.000 L 55.51 mol 1 L 1 m 15.9994 1.00794 10 kg 6.0 10 molecules 5 55.51 mol.4 10 molecules 1 mol 5. We use Eq. 17-4. N 1molecule 100 cm J 17 P NkT P kt 1.8 10 K 4 10 Pa 1cm m K 55. Assume the gas is ideal at those low pressures, and use the ideal gas law. P 1 6 N P 110 N m 8 molecules 10 m NkT 10 kt 1.8 10 J K 7 K m 1 cm 00 molecules cm 56. We assume an ideal gas at STP. Example 17-10 shows that the molar volume of this gas is.4 L. We calculate the actual volume of one mole of gas particles, assuming a volume of l and then find the ratio of the actual volume of the particles to the volume of the gas. molecules gas 10.4 L1 10 m 1L 6.0 10 molecules.0 10 m molecule 7.10 4, 0
The molecules take up less than 0.1% of the volume of the gas.