Chapter 10 - Properties of Gases

what is a gas?

a substance that has no well-defined boundaries but diffuses rapidly to fill any container in which it is placed

what is temperature?

the measure of the hotness or coldness of a body

what is absolute zero?

the lowest possible temperature (-273°C or 0K)

how is °C converted to kelvin?

+273 (0°C = 273K)

what is the value of normal atmospheric pressure?

100kPa / 1×10⁵ Pa

what is the value of standard temperature?

273K

what is the value of standard pressure?

100kPa

what is Boyle’s Law?

states that, at a constant temperature the volume of a fixed mass of gas is inversely proportional to its pressure

PV = k (constant)

why does pressure increase as volume decreases?

gas molecules have less space to move around in, meaning they collide with each other more often, causing an increase in pressure

what is a volatile liquid?

liquid with a low boiling point

what volatile liquid is used in the relative molecular mass of a volatile liquid experiment?

propanone (acetone) or cyclohexane

what is Charles’ Law?

states that at a constant pressure, the volume of a fixed mass of gas is directly proportional to its temperature measured in kelvins

V / T = k (constant)

why does volume increase as temperature increases?

as temperature increases, gas molecules provided with more kinetic energy allowing them to move faster and collide with each other and their container more often, meaning volume needs to increase

what is the formula of the Combined Gas Law?

P₁V₁ / T₁ = P₂V₂ / T₂

(P - pressure, V - volume, T - temperature)

what is Gay-Lussac’s Law?

states that, in a reaction between gases, the volume of the reacting gases and volumes of any gaseous products are in ratio of small, whole numbers provided volumes are at same temperature and pressure

(e.x 2H₂ + O₂ = 2H₂O)

When gases react with each other, their volumes combine in simple whole-number ratios, as long as the temperature and pressure stay the same.

what is Avogadro’s Law?

states that, equal volumes of gases contain equal numbers of molecules under the same conditions of temperature and pressure

(e.x 1 mol of hydrogen occupies same volume as 1 mol of methane)

what are the assumptions of Kinetic Theory of Gases?

• C – Collisions are perfectly elastic (no energy lost in collisions)

• R – Random motion of particles (continuous, rapid, random movement and collisions with each other and container)

• A – Absence of attractive/repulsive forces between molecules

• V – Volume of individual gas particles is negligible compared to gas’ total volume

• E – Energy (kinetic) of gas molecules in sample is proportional to temperature in Kelvin

what are limitations to the Kinetic Theory of Gases?

• not valid to say volume of gas molecules is always negligible compared to the space they occupy

• all gases have tiny repulsive forces between molecules (intermolecular forces)

what type of gas is the Kinetic Theory of Gases true for?

an ideal gas

under what conditions do real gases come close to ideal gas behaviour?

• low pressure - widely spaced molecules

• high temperatures - rapid movement prevents intermolecular forces

what is an ideal gas?

a gas that perfectly obeys all the assumptions of the Kinetic Theory of Gases under all conditions of temperature and pressure

how do real gases differ from ideal gases?

• forces of attraction and repulsion do exist between molecules

• volume of molecules is not negligible, they occupy space

what is the Ideal Gas Formula?

p V= n R T

(pressure, volume, number of moles, universal gas constant (R) (8.31), temperature (K))

(units must be in m³, Pa and K)

which of noble gases is most expected to behave like an ideal gas?

Helium

particles have the smallest volume (closest to negligible)

weakest intermolecular forces (Van-der-Waals)