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## PowerPoint Slideshow about 'How Volume Varies With Temperature' - Mia_John

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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).

Let’s take a closer look at temperature before we try to find the exact relationship of V vs. T.

Is 20C twice as hot as 10C?

Is 20 kg twice as heavy as 10 kg?

Temperature scalesNo. 68F (20C) is not double 50F (10C)

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 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…

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

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.
- –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 K

- Notice that kelvin is represented as K not K.

Kelvin Practice

Absolute zero is –273C or 0 K

What is the approximate temperature for absolute zero in degrees Celsius and kelvin?

Calculate the missing temperatures

0C = _______ K 100C = _______ K

100 K = _______ C –30C = _______ K

300 K = _______ C 403 K = _______ C

25C = _______ K 0 K = _______ C

273

373

–173

243

27

130

298

–273

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

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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