1、Charless Law,The relationship between temperature and volume,1,學習交流PPT,If we place a balloon in liquid nitrogen it shrinks:,How Volume Varies With Temperature,So, gases shrink if cooled. Conversely, if we heat a gas it expands (as in a hot air balloon).,Lets take a closer look at temperature before

2、we try to find the exact relationship of V vs. T.,2,學習交流PPT,No. 68F (20C) is not double 50F (10C) Yes. 44 lb (20 kg) is double 22 lb (10 kg) Whats the difference? Weights (kg or lb) have a minimum value of 0. But the smallest temperature is not 0C. We saw that doubling P yields half the V. Yet, to i

3、nvestigate the effect of doubling temp-erature, we first have to know what that means. An experiment with a fixed volume of gas in a cylinder will reveal the relationship of V vs. T,Temperature scales,Is 20C twice as hot as 10C? Is 20 kg twice as heavy as 10 kg?,3,學習交流PPT,Temperature vs. Volume Grap

4、h (fig.7,8 pg.430), 273,25 mL at 22C 31.6 mL, 23.1 mL Y=0.0847x + 23.137,4,學習交流PPT,If a volume vs. temperature graph is plotted for gases, most lines can be interpolated so that when volume is 0 the temperature is -273 C. Naturally, gases dont really reach a 0 volume, but the spaces between molecule

5、s approach 0. At this point all molecular movement stops. 273C is known as “absolute zero” (no EK) Lord Kelvin suggested that a reasonable temp-erature scale should start at a true zero value. He kept the convenient units of C, but started at absolute zero. Thus, K = C + 273. 62C = ? K: K=C+273 = 62

6、 + 273 = 335 K Notice that kelvin is represented as K not K.,The Kelvin Temperature Scale,5,學習交流PPT,What is the approximate temperature for absolute zero in degrees Celsius and kelvin? Calculate the missing temperatures 0C = _ K100C = _ K 100 K = _ C 30C= _ K 300 K = _ C 403 K = _ C 25C = _ K0 K = _

7、 C,Kelvin Practice,273,373, 173,243,27,130,298, 273,Absolute zero is 273C or 0 K,6,學習交流PPT,Looking back at the temperature vs. volume graph, notice that there is a direct relationship. It can be shown that V/T = constant Read pages 432-3. Answer these questions: Give Charless law in words & as an eq

8、uation. Charless Law: as the temperature of a gas increases, the volume increases proportionally, provided that the pressure and amount of gas remain constant, V1/T1 = V2/T2,Charless Law,7,學習交流PPT,A sample of gas occupies 3.5 L at 300 K. What volume will it occupy at 200 K?,If a 1 L balloon is heated from 22C to 100C, what will its new volume be?,Do questions 16, 17, 19 on page 434,V1 = 3.5 L, T1 = 300K, V2 = ?, T2 = 200K Using Charles law: V1/T1 = V2/T2 3.5 L / 300 K = V2 / 200 K V2 = (3.5 L/300 K) x (200 K) = 2.3 L,V1 = 1 L, T1 = 22C = 295