charleslaw查尔斯定律.ppt
Charless Law,The relationship between temperature and volume,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 we try to find the exact relationship of V vs.T.,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 investigate 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?,Temperature vs.Volume Graph(fig.7,8 pg.430),273,25 mL at 22C31.6 mL,23.1 mLY=0.0847x+23.137,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 molecules 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+273=335 KNotice that kelvin is represented as K not K.,The Kelvin Temperature Scale,What is the approximate temperature for absolute zero in degrees Celsius and kelvin?Calculate the missing temperatures0C=_ K100C=_ K100 K=_ C 30C=_ K300 K=_ C 403 K=_ C25C=_ K0 K=_ C,Kelvin Practice,273,373,173,243,27,130,298,273,Absolute zero is 273C or 0 K,Looking back at the temperature vs.volume graph,notice that there is a direct relationship.It can be shown that V/T=constantRead pages 432-3.Answer these questions:Give Charless law in words&as an equation.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,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=200KUsing Charles law:V1/T1=V2/T23.5 L/300 K=V2/200 KV2=(3.5 L/300 K)x(200 K)=2.3 L,V1=1 L,T1=22C=295 KV2=?,T2=100 C=373 KV1/T1=V2/T2,1 L/295 K=V2/373 KV2=(1 L/295 K)x(373 K)=1.26 L,
