Chem 101L: Gas Laws

What is the ideal gas law?

PV=nRT

What do the variables in the ideal gas law represent?

• P = pressure (atm)

• V = volume (L)

• n = moles

• R = 0.08206 L·atm/mol·K

• T = temperature (K)

What is the value of the gas constant R?

0.08206 L·atm/(mol·K)

Standard temperature and pressure (STP)?

273.15 K and 1.00 atm.

Volume of 1 mole of ideal gas at STP?

22.414 L.

What assumptions define an ideal gas?

No intermolecular forces & negligible particle volume.

State Boyle’s Law.

P∝1/V​ (inverse relationship).

Mathematical form of Boyle’s Law?

PV=k (constant).

Variables held constant in Boyle’s Law?

Temperature & number of moles (T and n constant).

What happens to pressure when volume decreases?

Pressure increases.

What happens to pressure when volume increases?

Pressure decreases.

Relationship between pressure and number of moles?

P=kn

Variables held constant in the pressure–amount relationship?

Volume & temperature (V and T constant).

Why does pressure increase with more moles?

More particles → more collisions with the container walls.

State Amontons’ Law.

P∝T

Mathematical form?

P=kT

Variables held constant in Amontons’ Law?

Volume & moles.

Why does pressure increase as temperature increases?

Higher temperature → faster molecules → more collisions.

Why do gases exert pressure?

Collisions of gas molecules with container walls.

How does temperature affect molecular motion?

Higher temperature → higher velocity → higher pressure.

What is absolute zero?

0 K, theoretical temperature with no molecular motion.

Composition of dry air?

~78% N₂, 21% O₂, 1% Ar, 0.03% CO₂.

Why can air be treated as an ideal gas?

Uniform mixture with low intermolecular forces.

Effective molar mass of dry air?

28.96 g/mol.

Density of dry air at 25°C?

0.001185 g/mL.

What is vapor pressure?

Pressure exerted by a vapor in equilibrium with its liquid

Does water vapor significantly affect gas law measurements?

Only minimally — at 100% humidity, only ~3% of air is water vapor.

Temperature must always be converted to what unit for gas laws?

Kelvin.

Formula to convert Celsius to Kelvin?

K=∘C+273.15

Standard pressure units in gas law calculations?

Atmospheres (atm).

What happens to gas pressure if temperature decreases?

Pressure decreases.

What happens to gas pressure if more gas is added at constant volume?

Pressure increases.

What happens to gas pressure if volume decreases at constant temperature?

Pressure increases (Boyle’s Law).

What determines slope in a P vs. 1/V graph?

Number of moles × temperature.

Ideal Gas Law:

PV=nRT

Boyle’s Law:

PV=k

Pressure–Amount Relationship:

P=kn

Amontons’ Law:

P=kT

Temperature Conversion:

K=∘C+273.15