Charles’ Law

WARMUP1.Graph the data2.How are temperature and volume related?3.At what temperature would volume be zero?

volu

me

(cm

3)

Temperature (⁰C)

T and V have a direct, linear relationship

V1 = V2

T1 T2

Temp. (⁰C) Volume (cm3)

30 80-10 70-50 60-90 50-130 40-170 30-210 20-250 10

-273⁰C

More Gas LawsCharles

Gay-Lussac Avagadro

V1 = V2

T1 T2

(V1) = 2.5cm3

291.5K 311.5K

Answer: 2.3 cm3

1. Some students think that teachers are full of hot air. If Ms Jonson takes a deep breath of air at 18.5°C and it heats to 38.5°C and the volume expands to 2.5 cm3, what was the starting volume of air? Assume constant pressure.

P1 = cons. P2 = cons.

V1 = ? V2 = 2.5 cm3

T1 = 18.5°C T2 = 38.5°C

291.5 K 311.5 K

2. A sample of nitrogen occupies 250 mL at 25°C. What volume will it occupy at 95°C?

V1 T1

T2

Initial After

P1 = P2 =

V1 = V2 =

T1 = T2 =25°C 298 K

95°C368 K

?250 mL

----- -----

K 298

K 368 X mL 250

V2 = 310 mL

2

2

1

1

TV

TV

1

2 x 12

TTV

V

3. Oxygen gas is at a temperature of 40.0°C when it occupies a volume of 2.30 L. To what temperature (in °C) should it be raised to occupy a volume of 6.50 L?

V1

T1

T2 V2

Initial After

P1 = P2 =

V1 = V2 =

T1 = T2 =40.0°C 313 K

6.50 L

?

2.30 L

----- -----

L 2.30

K313 X L 6.50

T2 = 885 K

2

2

1

1

TV

TV

1

1 x 22

VTV

T

wait…need Celsius -273

T2 = 612°C

Gay-Lussac’s Law

Temperature

Pre

ssur

e

2

2

1

1

TP

TP

How are pressure and temperature related?

P and T have a direct, linear relationship

1. Before a trip from New York to Boston, the pressure of an automobile tire is 1.8 atm at 20.°C. At the end of the trip, the pressure gauge reads 1.9 atm. What is the new Celsius temperature of the air inside the tire? (Assume the tires had a constant volume throughout the whole trip).

Initial After

P1 = P2 =

V1 = V2 =

T1 = T2 =

P1

T1 P2

T2

1.8 atm

1.9 atm

-------- --------

20°C = 293 K ?

2

2

1

1

TP

TP

1

21 2

PPT

T

atm 1.8

atm1.9 X K293

T2 = 309.3 K or 36°C

2. Determine the pressure (in atm) when a constant volume of gas at standard pressure is heated from 20.0°C to 30.0°C. P1T1T2

P2

Initial After

P1 = P2 =

V1 = V2 =

T1 = T2 =20°C

293 K

1.00 atm ?

30°C303 K

----- -----

K293

K303 X atm 1.00

P2 = 1.03 atm

2

2

1

1

TP

TP

1

2 x 12

TTP

P

Rising Water DemoProcedure: Half fill the dish with tap water, add some food coloring, and mix. Light the candle. Place the 250ml beaker over the candle and press it to the bottom of the dish. Observe and explain!

Why does the candle go out?

Lack of oxygen.

Why does the water level rise?

Difference in air pressure causes suction. The cause of the pressure differential is interesting think about the combustion reaction…

The balanced reaction for the combustion of candle wax is given as:

2C20H42(s) + 61O2(g) 40CO2(g) + 42H2O(l)

There is a net loss of 21 moles of gas as O2 is used and CO2 is made. Also, CO2 is more water soluble than O2 (stays dissolved in the liquid rather than being present as gas).

Avogadro’s Law: as moles of gas decreases, volume decreases.

Avogadro’s Law

1 L of Helium

1 L of Oxygen

equal numbers of molecules (moles)

of gas at the same temperature

(with same KE and speed)

V1 = V2

n1 n2

should exert the same pressure,therefore should

have the same volume

1 mole of ANY gas at STP will occupy 22.4 L

molar volume = 22.4 L/mole

1. 4.55 moles hydrogen gas occupy 75.0 mL at STP. Under the same STP conditions, how many moles of gas would be present in a 1680 ml sample?

Initial After

P1 = P2 =

V1 = V2 =

n1 = n2 =

T1 = T2 =

75.0 mL

?

-----

n2 = 102 moles

V1 = V2

n1 n2

----- -----

-----

1680 ml

4.55 moles

n2 = n1V2

V1n2 = (4.55 moles)(1680ml)

(75.0ml)

2. A 5.6 mole sample of air is inside a 2.0L soda bottle. What volume would 0.34 moles of air occupy under the same conditions?

V1n1

V2

Initial After

P1 = P2 =

V1 = V2 =

n1 = n2 =

T1 = T2 =

0.34 moles

?

-----

V2 = 0.12 L

V1 = V2

n1 n2

n2

----- -----

-----

2.0L

5.6 moles

V2 = V1 n2

n1V2 = (2.0L)(0.34 moles)

(5.6 moles)

Gas Law Mystery GameDirections:

You will be given three TIMED gas law problems. (Exactly 3 minutes to do each

problem…so work together). Your job is to find an answer to each mystery problem.

The sum of the answers to all three mystery problems is: -189.088 (ignoring sig fig

rules)

a. You have 60.2 mL of gas. You increase the volume to 701 mL by increasing the temperature to 502°C while holding pressure constant. What was the starting temperature of the gas (in °C)?

b. A 22.0 cm3 sample of oxygen gas expands to 78.0 cm3. If the original pressure was 570. mmHg, what is the new pressure (in atm)?

c. A 1.2 mole sample of acetylene gas has an initial pressure of 699 mm Hg at 40.0°C. When 0.6 moles of acetylene gas are added to the glass container, the volume increases to 25.0 ml. What was the initial volume of acetylene? Assume constant temperature and pressure.

Add your answers to all 3 mystery problems!

(volunteers to show work???)

a b c ANSWER (no units)+ + =

-206 °C

+0.212 atm

+16.7 ml

= -189.08

8