Gases Chemistry Review

advertisement

Gases

Chemistry Review

Atom – smallest piece of an element

Molecule – smallest piece of a compound – two or more atoms chemically bonded

Mole – counting number equal to 6.022 x 10 23

Molar Mass – number of grams of a substance per mole – equal to the atomic mass on the periodic table

Review

 How many moles in 5.5g of hydrogen gas?

 How many molecules in 2.5 moles of oxygen?

 What is the mass of one molecule of helium gas?

Kinetic Theory

 Matter is made of particles in continuous motion

 Particles move in random directions at a variety of speeds

 Particles of gases are on average very far apart from one another

 Molecules of gases interact only when they collide

 Collisions are perfectly elastic (no loss of kinetic energy)

Pressure Units

 1atm = 760mmHg = 760torr = 101kPa

 STP – standard temp and pressure (0 ° C and 1 atm)

Gas Laws

Volume is proportional to the temperature –

Charles Law ( V

1

/T

1

= V

2

/T

2

)

Volume is inversely prop to temp – Boyles Law

( P

1

V

1

= P

2

V

2

)

Pressure is prop to temp – Gay-Lussac’s Law

( P

1

/T

1

= P

2

/T

2

)

Combined Gas Law puts them together

( P

1

V

1

/T

1

= P

2

V

2

/T

2

)

Ideal Gas

 One that follows all kinetic theory

 Volume of a gas also depends on the number of moles

 Ideal Gas Law

PV = nRT R = .0821 L •atm/ mol•K

Examples

 Determine the volume of 1.00 mole of a gas at

STP.

 A container of oxygen at STP has a volume of

10.0 L. What is the mass of the gas?

Examples

 A helium party balloon has a radius of 18.0cm at 20 ° C and 1.05 atm. How many moles of He are in the balloon and what is the mass of the gas in the balloon?

 An auto tire is filled to a pressure of 200kPa at

10 ° C. After driving 100km, the temp rises to

40 ° C. What is the pressure now?

Kinetic Energy of Molecules

 The average KE of molecules is directly proportional to the temp

KE = ½ mv 2 = 3/2 kT k – Boltzman’s Constant = 1.38x10

-23 J/K

Example

 What is the average KE of gas molecules at

37 ° C?

Average Velocity

 Also called root mean square velocity

 v rms

= 3 kT

M m – mass (in kg) of one molecule of the gas

Example

 What is the rms speed of an oxygen molecule at 20 ° C?

Download