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Gases Part 1

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Gases

Part 1

Elements that exist as gases at 250C and 1 atmosphere

Physical Characteristics of Gases

- Gases assume the volume and shape of their containers.
- Gases are the most compressible state of matter.
- Gases will mix evenly and completely when confined to the same container.
- Gases have much lower densities than liquids and solids.

Force

Area

Barometer

Pressure =

(force = mass x acceleration)

Units of Pressure

1 pascal (Pa) = 1 N/m2

1 atm = 760 mm Hg = 760 torr

= 101,325 Pa = 14.7 psi = 29.92 in. Hg

10 miles

0.2 atm

4 miles

0.5 atm

Sea level

1 atm

P α 1/V

This means Pressure and Volume are INVERSELY PROPORTIONAL if moles and temperature are constant (do not change). For example, P goes up as V goes down.

P1V1 = P2 V2

Robert Boyle (1627-1691). Son of Earl of Cork, Ireland.

If n and P are constant, then V α T

V and T are directly proportional.

V1 V2

=

T1 T2

- If temperature goes up, the volume goes up!

Jacques Charles (1746-1823)

If n and V are constant, then P α T

P and T are directly proportional.

P1 P2

=

T1 T2

If temperature goes up, the pressure goes up!

Joseph Louis Gay-Lussac (1778-1850)

- The good news is that you don’t have to remember all three gas laws! Since they are all related to each other, we can combine them into a single equation. BE SURE YOU KNOW THIS EQUATION!
P1 V1 P2 V2

=

T1 T2

STP in chemistry stands for Standard Temperature and Pressure

Standard Pressure = 1 atm (or an equivalent)

Standard Temperature = 0 deg C (273 K)

STP allows us to compare amounts of gases between different pressures and temperatures

Va number of moles (n)

Constant temperature

Constant pressure

V = constant x n

V1/n1 = V2/n2

Boyle’s law: V a (at constant n and T)

Va

nT

nT

nT

P

P

P

V = constant x = R

1

P

Charles’ law: VaT(at constant n and P)

Avogadro’s law: V a n(at constant P and T)

R is the gas constant

PV = nRT

R =

(1 atm)(22.414L)

PV

=

nT

(1 mol)(273.15 K)

The conditions 0 0C and 1 atm are called standard temperature and pressure (STP).

PV = nRT

R = 0.082057 L • atm / (mol • K)

Experiments show that at STP, 1 mole of an ideal gas occupies 22.414 L.

m

V

PM

=

RT

dRT

P

Density (d) Calculations

m is the mass of the gas in g

d =

M is the molar mass of the gas

Molar Mass (M ) of a Gaseous Substance

d is the density of the gas in g/L

M =

M =

dRT

P

A 2.10-L vessel contains 4.65 g of a gas at 1.00 atm and 27.00C. What is the molar mass of the gas?