IB CHEM 1 - Lesson 1 Part 4: Average Kinetic Energy

In kinetic theory, what does temperature measure?

The average kinetic energy of particles in a substance

What’s the SI unit of temperature, and why do we use it here?

Kelvin (K); average kinetic energy is directly proportional to T in Kelvin

Write the relationship between average Ek and T (ideal gas).

Average Ek is proportional to T (more precisely Ek = 3/2 kT per particle, = 3/2 RT per mole)

At the same temperature, which gas has higher average kinetic energy?

Neither—all gases have the same average Ek at the same T

At the same T, which gas moves faster—lighter or heavier?

Lighter gases move faster (higher average speed), even though average Ek is the same

Convert between K and °C.

T(K) = θ(°C) + 273.15

What is 0 K?

Absolute zero—particles have no kinetic energy (theoretical limit)

Why does temperature rise on solid-only or liquid-only segments?

Energy increases particle kinetic energy → T goes up

Why is temperature constant during melting/boiling?

Energy is used to overcome intermolecular forces (potential energy change), not to increase Ek

Endo or exo: melting? freezing?

Melting = endothermic, freezing = exothermic

Endo or exo: boiling? condensation?

Boiling = endothermic, condensation = exothermic

Endo or exo: sublimation? deposition?

Sublimation = endothermic, deposition = exothermic

Two differences between boiling and evaporation.

Boiling: throughout liquid, at bp when Pvap = Patm; Evaporation: surface only, below bp

Why does water boil at a lower T on a mountain?

Lower external pressure, so Pvap = Patm at a lower temperature

How do spacing, order, motion change across states?

Spacing increases, order decreases, motion/energy increases from solid to gas

What would you see during melting and boiling?

Melting: shape lost, volume ~constant; Boiling: bubbles form throughout liquid

What would you see during condensation and freezing?

Condensation: droplets on cool surfaces; Freezing: liquid becomes rigid/ordered

What do (s), (l), (g), (aq) mean?

Solid, liquid, gas, aqueous (dissolved in water)

When is water (aq) vs (l)?

(l) for pure liquid water; (aq) when a solute is dissolved in water

Which has higher average Ek: N2 at 150 °C or Ar at 350 °C?

Ar at 350 °C—higher Kelvin temperature → higher average Ek

Why compare in Kelvin, not °C?

Proportionality of average Ek is to Kelvin; °C is an offset scale

Why does heating a sealed gas raise pressure?

Higher particle speeds → more frequent/forceful collisions with container walls

What quantity is changing at a plateau if T is constant?

Potential energy / phase proportion (solid↔liquid or liquid↔gas), not average Ek