Gases

States of Matter• Solid:

• Definite Shape • Definite Volume• Incompressible

• Liquid: • Indefinite Shape• Definite Volume• Not Easily Compressed

• Gas: • Indefinite Shape• Indefinite Volume• Easily compressed

Gas• Kinetic Theory: All matter

consists of tiny particles that are in constant motion– Particles of Gas:

SmallFastRandom

MotionCollide A LOTCompressible

Can be affected by: Pressure, Volume, Amount (mols), Temperature

Pressure and VolumeUnits of Pressure:

1 mm Hg = torr1 atm = 760mm of Hg (Mercury)1 atm = 14.696 psi (pounds per square inch)1 atm = 101.325 kP (kPa = 1000Pa)pascals (Pa) is the systems international (SI)

What do you think causes pressure on the surface of an object that contains a gas?

Pressure and Volume

• What do you think happens to the volume of a gas if the pressure increases?

Boyle’s Law• If the temperature is constant, as the pressure

of a gas increases, the volume decreases.

P1 x V1 = P2 x V2

• Use Boyle’s Law….A balloon contains 30.0L of helium gas at 103kPa.

What is the volume of the helium when the balloon rises to an altitude where the pressure is only 25.0kPa?

• Nitrous oxide (N2O) is used as an anesthetic. The pressure on 2.50L of N2O changes from 105kPa to 40.5kPa. If the temperature does not change, what will the new volume be?

Temperature and Volume

• Temperature:– Celsius (ᵒC)– Kelvin (K)

0 K = -273.15ᵒC ….. Coldest possible temperature

When using gas laws, the temperature MUST be in Kelvin!!

K = ᵒC + 273

Temperature and Volume

• If the pressure is constant, what happens to the volume of a gas as the temperature is increased?

Charles’s Law• If the pressure is constant, as the temperature

of a gas increases, the volume increases.

• Use Charles’s Law…A balloon inflated in a room at 24ᵒC has a volume

of 4.00L. The balloon is then heated to a temperature of 58ᵒC. What is the new volume if the pressure remains constant?

• If a sample of gas occupies 6.80L at 325ᵒC, what will its volume be at 25ᵒC if the pressure does not change?

Pressure and Temperature

• If the volume is constant, what happens to the pressure of a gas as the temperature increases?

Gay-Lussac’s Law• If the volume is constant, as the temperature

is increased, the pressure increases.

• Use Gay-Lussac’s LawThe gas in a used aerosol can is at a pressure of

103kPa at 25ᵒC. If the can is thrown onto a fire, what will the pressure be when the temperature reaches 928ᵒC?

• A sample of nitrogen gas has a pressure of 6.58kPa at 539K. If the volume does not change, what will the pressure be at 211K?

Avogadro's hypothesisEqual volumes of gases at the same temperature

and pressure contain equal numbers of molecules• 1 mole of any gas (6.02 x 1023 gas molecules) at

STP occupies approximately 22.4 liters volumeSTP: Standard Temperature and Pressure

0°C 1 atmosphere

Combined Gas Law

• If the amount of gas is constant…

Ideal Gas Law

R = the ideal gas constant = 8.31 (L x kPa)/(K x mol) OR = 0.0821 (L x atm)/(K x mol)

Which one you use depends on the units that you are using…

Nitrate salts (NO3-) when heated can produce nitrites (NO2

-) plus oxygen (O2). A sample of potassium nitrate is heated and the O2 gas produced is collected in a 750ml flask. The pressure of the gas in the flask is 2.80 atmospheres and the temperature is recorded to be 53.6 °C.

• How many moles of O2 gas were produced?

2NO3- 2NO2

- + O2

PV = nRTP = 2.8 atmT = 53.6°C + 273 = 326.6KV = 750mL = 0.750Ln = ? molR = 0.0821

(2.80 atm )( 0.750 L) = n (0.0821) (326.6K)2.1 = n (26.81)

n = (2.1) / (26.81 n = 0.078 mol O2 were produced

• A deep underground cavern contains 2.24x106L of methane gas (CH4) at a pressure of 1.5x103kPa and a temperature of 315K. How many kilograms of CH4 does the cavern contain?

Dalton’s Law

• In a mixture of gases, the total pressure is the sum of the partial pressures of the gases

Ptotal = P1 + P2 + P3 + …

Graham’s Law

• How does the molar mass of a gas affect its movement?

Graham’s Law

• Gases of lower molar masses diffuse and effuse faster than gases of higher molar mass