GAS LAWS

• Gordon, Judy. "Measuring gases." In Nelson Chemistry VCE Units 1&2, edited by Jenny Sharwood, 436-459. 2nd ed. Melbourne, Victoria: Thomson & Nelson, 2007.
• YouTube, (2015). Ideal Gas Problems: Crash Course Chemistry #13. Web. 7 Nov. 2015.
• YouTube, (2015). Real Gases: Crash Course Chemistry #14'. Web. 19 Oct. 2015.

GAS LAWS AND PREDICTING THE BEHAVIOUR OF GASES

IDEAL GASES

PV = nRT

THE IDEAL GAS LAW

PRESSURE

EXAMPLES

P = F/A

A hypothetical 'ideal' gas refers to one where the particles have no mass and no force acting between them.

pressure = force / area

VOLUME

1 Pa = 1 N/m^2

THE UNIVERSAL GAS CONSTANT

n = V / Vm

Pascals (Pa) is the SI unit for pressure. Since the unit is small generally kilopascals (kPa) or atmospheres (atm) are used.

PV = nRT

R = 8.315 LkPa/Kmol

Where n is the number of moles and Vm is the molar volume.

= 11.2 / 22.4

= 0.5

1 kPa = 1000 Pa

1 atm = 101325 Pa = 760 mmHg

At STP Vm = 22.4 mol/L

At SLC Vm = 24.5 mol/L

V = (nRT) / P

International units for pressure include the British Imperial unit, pounds per square inch (psi).

CH4 (methane)

V = 11.2 L

@ STP

m = ?

m = nM

1 mmHg refers to one millimeter of mercury on a Torricellian barometer.

R = 8.31

V = ?

n = 1

T = 1000°C = 1273 K

P = 0.5 atm = 50.6625 kPa

= 0.5 * 16

= 8 g

= (1 * 8.31 * 1273) / 50.6625

= 208.1 L

PV = nRT

VOLUME

BOYLE'S LAW

TEMPERATURE

O^2 (oxygen)

V = 0.400m^3 = 400 L

@ SLC

PV = constant

Volume refers to the amount of space the gas has to exist inside of. Meters cubed (m^3) is the SI unit for volume. Litres (L) is more commonly used.

Kelvin (K) is the SI unit or temperature but the more common unit used is Celsius (°C). International units include Fahrenheit (°F) which is used in America.

P1 * V1 = P2 * V2

n = V / Vm

= 400 / 24.5

= 16.33 mol

JOSEPH GAY-LUSSAC

AMADEO AVAGADRO

Think of an inflated balloon. As you push on it, decrease its volume, the pressure inside the balloon increases till it bursts.

0 K, - 237°C, is know as absolute zero where all movement of all particles stops.

-273°C = 0 K

0°C = 273 K

100°C = 373 K

V / n = constant

V n

Volume (V) is proportional to the number of moles (n) of a gas if the temperature and pressure are identical.

pressure (kPa) * volume (L)

=

moles * constant * temperature (K)

CHARLES' LAW

START

V / T = constant

V1 / T1 = V2 / T2

If you place a dented ping pong ball under hot water the air inside expands and the ball is restored to its original state. An increase in temperate causes and increase in volume.

REAL GASES

THE IDEAL AND COMBINED GAS EQUATIONS

The ideal gas law is only accurate for some real gases under low pressures and high temperatures.

PV = nRT

PV / T = C

The ideal gas law can be found by combining Avogadro's law with the combined gas equation.

THE COMBINED GAS LAW

C = nR

PV / T = nR

PV = nRT

Avogadro's law states that C is proportional to n, the number of moles with the proportionality factor being R.

SLC

STP

Standard temperature and pressure.

Standard laboratory conditions.

P1V1 / T1 = P2V2 / T2

Gases have mass and forces operating in between them, properties that cannot be factored into the ideal gas law. The law requires modification to provide accurate results over a larger range of pressures and temperatures.

VAN DER WAALS EQUATION

0°C

1.0 atm

101.3 kPa

25°C

1.0 atm

101.3 kPa

PV = nRT

PV / nT = R = 8.315

These standard collection conditions allow for comparisons to be made between different data sets. At these conditions the combined gas equation is used.

(pressure1 * volume1) / temperature1

=

(pressure2 * volume2) / temperature2

Where 'a' and 'b' represent different correction constants depending on the gas involved.

The combined gas equation combines Boyle's and Charles' equations to equal one single constant.

The law above replaces the constant with an duplicate of left hand side equation, it is used for comparison if variables are changed.

START