Chapter 18 – Gas Laws and the Ideal Gas Equation

What is the SI unit of pressure?

The Pascal (Pa), equivalent to N/m².

What is the SI unit of volume?

Cubic metre (m³).

What is the SI unit of temperature in gas laws?

Kelvin (K).

What is 0°C in Kelvin?

273 K.

What does the symbol R represent in the ideal gas law?

The ideal gas constant, 8.31 J/mol·K.

State Boyle's Law and its mathematical expression.

At constant temperature, pressure is inversely proportional to volume: pV = constant.

State Charles's Law and its mathematical expression.

At constant pressure, volume is directly proportional to absolute temperature: V ∝ T.

State the Pressure Law and its mathematical expression.

At constant volume, pressure is directly proportional to absolute temperature: P ∝ T.

Write the ideal gas equation.

pV = nRT

What is the value of R?

8.31 J/mol·K

How do you rearrange the ideal gas law to find the number of moles?

n = pV / RT

What are the units for each term in pV = nRT?

p in Pa, V in m³, n in mol, R in J/mol·K, T in K

What is Avogadro's constant?

6.022 × 10²³ particles/mol

How do you calculate number of molecules?

N = n × N_A

Define a mole of gas.

The amount of substance containing the same number of particles as 12 g of carbon-12.

How do you convert °C to K?

T(K) = T(°C) + 273

Convert cm³ to m³.

Divide by 1,000,000.

Convert dm³ to m³.

Divide by 1,000.

Why do gas particles exert pressure?

They collide with the container walls, changing momentum and exerting force.

What happens to particle speed as temperature increases?

Average kinetic energy increases, so speed increases.

What is meant by elastic collisions?

Collisions where kinetic energy is conserved.

Why must temperature be in Kelvin for gas laws?

Because it is directly proportional to kinetic energy.

What is absolute zero?

0 K - the temperature where particle motion theoretically stops.

Why is the internal energy of an ideal gas only kinetic?

Because it assumes no intermolecular forces.

State the kinetic theory equation.

pV = (1/3)Nm⟨c²⟩

What is the average kinetic energy of a gas particle?

KE = (3/2)kT

What does Boltzmann constant represent?

Relates temperature and average kinetic energy; k = R/N_A

When do gases deviate from ideal behaviour?

At high pressure and low temperature.

Why do real gases deviate at high pressure?

Particle volume and intermolecular forces become significant.

Describe the graph for Boyle's Law.

Downward curve - pressure inversely proportional to volume.

Describe the graph for Charles's Law.

Straight line through origin - volume proportional to Kelvin temperature.

Describe the graph for the Pressure Law.

Straight line through origin - pressure proportional to Kelvin temperature.

What does the area under a p-V graph represent?

Work done by or on the gas.

What does each term in pV = nRT stand for?

Pressure, Volume, Moles, Ideal gas constant, Temperature.

What does each term in pV = (1/3)Nm⟨c²⟩ stand for?

N = number of molecules, m = mass, ⟨c²⟩ = mean square speed.

What is meant by mean square speed?

The average of the squares of molecular speeds.

If temperature doubles at constant volume, what happens to pressure?

It doubles.

If pressure triples at constant temperature, what happens to volume?

It reduces to one-third.

What happens to volume when temperature increases at constant pressure?

It increases proportionally.