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Charles's Law

Charles's Law. The relationship between temperature and volume. How Volume Varies With Temperature. If we place a balloon in liquid nitrogen it shrinks:. So, gases shrink if cooled. Conversely, if we heat a gas it expands (as in a hot air balloon).

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Charles's Law

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  1. Charles's Law The relationship between temperature and volume

  2. How Volume Varies With Temperature If we place a balloon in liquid nitrogen it shrinks: So, gases shrink if cooled. Conversely, if we heat a gas it expands (as in a hot air balloon). Let’s take a closer look at temperature before we try to find the exact relationship of V vs. T.

  3. Is 20C twice as hot as 10C? Is 20 kg twice as heavy as 10 kg? Temperature scales No. 68F (20C) is not double 50F (10C) Yes. 44 lb (20 kg) is double 22 lb (10 kg) What’s the difference? • Weights (kg or lb) have a minimum value of 0. • But the smallest temperature is not 0C. • 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…

  4. 30 25 20 Volume (mL) 15 10 5 0 100 Temperature (C) Temperature vs. Volume Graph (fig.7,8 pg.430) 25 mL at 22C 31.6 mL, 23.1 mL Y=0.0847x + 23.137 – 273

  5. The Kelvin Temperature Scale • 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 don’t really reach a 0 volume, but the spaces between molecules approach 0. • At this point all molecular movement stops.

  6. –273C is known as “absolute zero” (no EK) • Lord Kelvin suggested that a reasonable temperature scale should start at a true zero value. • He kept the convenient units of C, but started at absolute zero. Thus, K = C + 273. 62C = ? K: K=C+273 = 62 + 273 = 335 K • Notice that kelvin is represented as K not K.

  7. Kelvin Practice Absolute zero is –273C or 0 K What is the approximate temperature for absolute zero in degrees Celsius and kelvin? Calculate the missing temperatures 0C = _______ K 100C = _______ K 100 K = _______ C –30C = _______ K 300 K = _______ C 403 K = _______ C 25C = _______ K 0 K = _______ C 273 373 –173 243 27 130 298 –273

  8. Charles’s Law • 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 Charles’s law in words & as an equation. Charles’s 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

  9. 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 • 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 22°C to 100°C, what will its new volume be? V1 = 1 L, T1 = 22°C = 295 K V2 = ?, T2 = 100 °C = 373 K V1/T1 = V2/T2,1 L / 295 K = V2 / 373 K V2 = (1 L/295 K) x (373 K) = 1.26 L • Do questions 16, 17, 19 on page 434 For more lessons, visit www.chalkbored.com

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