Gas Law Review

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# Gas Law Review - PowerPoint PPT Presentation

Gas Law Review. Properties of Gases. No definite shape It fills its container Compressible With increases in pressure Low Density Molecules are far apart Intermolecular forces are ignored Diffusion Molecules can randomly spread out. Ideal Gas. Theoretical description of gases

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### Gas Law Review

Properties of Gases
• No definite shape
• It fills its container
• Compressible
• With increases in pressure
• Low Density
• Molecules are far apart
• Intermolecular forces are ignored
• Diffusion
• Molecules can randomly spread out
Ideal Gas
• Theoretical description of gases
• Disregard the volume of the molecule itself
• Disregard any attractive force between molecules
• Real gases stray from ideal gases at:
• LOW Temperatures
• HIGH Pressures

At STP (Standard temperature and pressure), all gases have a volume of 22.4 L.

• Standard Temperature:
• 0oC
• 273 K
• Standard Pressure:
• 101.3 kPa
• 1 atm
• 760 torr (or mmHg)
Charles Law
• The volume of a quantity of gas, at constant pressure, varies directly with the Kelvin temperature.
• Temperature MUST be in Kelvin! (oC + 273)

@ constant Pressure

A gas is collected at 58oC and has a volume of 225mL. What volume will it occupy at standard temperature, if pressure remains constant?

Since the temperature decreases, pressure must decrease!

T1= 331 K

V1 = 225 mL

T2 = 273 K

V2 = ?

186 mL = 0.186 L

Boyles Law
• As pressure increases, volume decreases.
• Temperature MUST be constant.

A sample of O2 gas at 0.947atm has a volume of 150mL. What would its volume be at 0.987atm if the temperature stay constant?

P1 = 0.947 atm

V1 = 150 mL

P2 = 0.987 atm

V2 = ?

144mL = 0.144L

Gay-Lussac’s Law

Volume is constant

* Remember, Temperature MUST be in Kelvin

An aerosol can has a pressure of 103 kPa at 25oC. It is thrown into a fire and its temperature increases to 928oC. What will its pressure be?

P1 = 103 kPa

P2 = ?

T1 = 25 oC + 273 = 298 K

T2 = 928 oC + 273 = 1201 K

P2 = 415 kPa

The volume of a gas-filled balloon is 30.0 L at 313 K and 153 kPa. What would the volume be at STP?

V1 = 30.0L

T1 = 313 K

P1 = 153 kPa

V2 = ?

T2 = 273 K

P2 = 101.3 kPa

V2 = 39.6 L

Ideal Gas Law

P = pressure

V = volume

(in Liters!)

n = moles

T = temperatre

(in Kelvin!)

R = gas constant

Gas constants

Find Volume
• What volume would be occupied by 1.00 moles of gas at 0oC at 1 atm pressure?

P = 1 atm

V = ?

n = 1 mol

R = 0.082 (because pressure is in atm)

T = 0oC + 273 = 273 K

V = 22.4L

• Equal volumes of gases at the same temperature and pressure contain equal numbers of particles.
• Molar Volume- for a gas, the volume that one mole occupies at STP
• Temp = 0oC or 273K
• Pressure = 1 atm or 101.3 kPa or 760 torr (mmHg)

1 mole = 22.4 Liters

Practice
• Determine the volume of a container that holds 2.4 mol of gas at STP.
1 H2 + 1 Cl2 2HCl
• If 100L of hydrogen gas react at STP, how many grams of hydrogen chloride can form?
Dalton’s Law of Partial Pressure
• The sum of the individual gas pressures equals the overall pressure of the mixture of gases.

If a container has 166 torr H2, 109 torr CO2 and 176 torr of O2, what is the total pressure of the mixture?

116 torr + 109 torr + 176 torr = 401 torr

Our atmosphere is made of 21% O2, 78% N2 and 1% other gases. At sea level (standard pressure), what is the partial pressure of oxygen?

760 torr x 0.21 = 159 torr O2

Diffusion
• The spontaneous spreading of particles
• The rate of diffusion depends on the velocities and masses of the molecules
• Effusion – the process by which a gas escapes from a small hole in a container
• Lighter gases ALWAYS diffuse/effuse faster than heavier molecules
Grahams Law of Diffusion
• The relative rates at which two gases, at the same temperature and pressure, will diffuse, vary inversely as the square root of the molecular mass of the gases.

**Always consider gas 1 the lighter gas

Compute the relative rates of diffusion of helium and argon.

• go to the periodic table for molar mass of He and Ar

Mass He = 4 g/mol

Mass Ar = 40 g/mol

So, helium diffuses 3x’s faster than argon.