# Gases Part 1 - PowerPoint PPT Presentation

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Gases Part 1. Elements that exist as gases at 25 0 C 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.

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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

### Boyle’s Law

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.

### Charles’s Law

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)

### Gay-Lussac’s Law

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)

### Combined Gas Law

• 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

### Ideal Gas Equation

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?