Kinetic Molecular Theory and Phase Changes: Key Concepts and Relationships
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86 Terms
What is Kinetic Molecular Theory (KMT)?
A theory that explains matter based on the motion and energy of its particles.
What are the 4 main ideas of KMT?
Particles are constantly moving; particles have kinetic energy; temperature relates to average kinetic energy; particles experience spaces/intermolecular forces.
What is kinetic energy?
The energy of motion.
What happens to average kinetic energy when temperature increases?
Average kinetic energy increases.
What happens to particle speed when temperature increases?
Particles move faster.
What is random motion?
Particles move continuously in unpredictable directions.
What are intermolecular forces (IMFs)?
Attractive forces between molecules or particles.
What is an elastic collision?
A collision where there is no overall loss of kinetic energy.
How are gas particles arranged?
Far apart with lots of empty space between them.
How do gas particles move?
Rapidly and randomly in all directions.
Why are gases highly compressible?
There is lots of empty space between gas particles.
Why do gases have low density?
Their particles are spread far apart.
Why do gases diffuse quickly?
Their particles move rapidly and have lots of space to move through.
How are particles arranged in a solid?
Very close together in fixed positions.
How do particles move in a solid?
They vibrate around fixed positions.
Why do solids have a fixed shape?
Strong attractions keep particles in fixed positions.
How are particles arranged in a liquid?
Close together but not in fixed positions.
How do particles move in a liquid?
They can move and slide past one another.
Why do liquids have a fixed volume but no fixed shape?
Particles stay close together but can move around.
What is plasma?
A high-energy state of matter containing ions and free electrons.
Give examples of plasma.
The Sun, stars, lightning, and neon signs.
What is melting?
The phase change from solid to liquid.
What is solidification/freezing?
The phase change from liquid to solid.
What is evaporation?
The phase change from liquid to gas at the surface.
What is condensation?
The phase change from gas to liquid.
What is sublimation?
The phase change directly from solid to gas.
What is deposition?
The phase change directly from gas to solid.
Which phase changes are endothermic?
Melting, evaporation, and sublimation.
Which phase changes are exothermic?
Freezing, condensation, and deposition.
What does endothermic mean?
A process that absorbs energy from the surroundings.
What does exothermic mean?
A process that releases energy to the surroundings.
What happens to particles during an endothermic phase change?
They absorb energy and become less restricted.
What happens to particles during an exothermic phase change?
They release energy and become more restricted.
What is the freezing point?
The temperature at which a liquid changes into a solid.
For a pure substance, how are melting point and freezing point related?
They occur at the same temperature.
How is evaporation different from boiling?
Evaporation occurs at the surface; boiling occurs throughout the liquid.
Can evaporation happen below the boiling point?
Yes, evaporation can occur below the boiling point.
Which particles escape during evaporation?
The higher-energy particles at the liquid's surface.
What happens during condensation?
Gas particles lose energy, slow down, and are attracted back into the liquid.
What is volatility?
How easily a substance evaporates.
What does high volatility mean?
The substance evaporates easily.
What type of IMF gives a substance high volatility?
Weaker intermolecular forces.
What type of IMF gives a substance low volatility?
Stronger intermolecular forces.
What is vapour pressure?
The pressure exerted by vapour above a liquid in a closed container.
What happens to vapour pressure when temperature increases?
Vapour pressure increases.
Why does vapour pressure increase with temperature?
More particles have enough kinetic energy to escape into the gas phase.
What is dynamic equilibrium?
When the rates of evaporation and condensation are equal.
Does dynamic equilibrium mean particles stop moving?
No. Evaporation and condensation continue at equal rates.
What happens to vapour pressure when intermolecular forces are stronger?
Vapour pressure decreases.
What happens to vapour pressure when intermolecular forces are weaker?
Vapour pressure increases.
What is the relationship between IMF strength and boiling point?
Stronger IMFs generally give a higher boiling point.
What is the relationship between volatility and boiling point?
Higher volatility generally means a lower boiling point.
What is the relationship between vapour pressure and boiling point?
Higher vapour pressure generally means a lower boiling point.
What is the normal boiling point?
The temperature where vapour pressure equals 101.3 kPa.
What pressure is used to define normal boiling point?
101.3 kPa.
How do you find normal boiling point on a vapour-pressure graph?
Find 101.3 kPa, move to the curve, then move down to the temperature.
What does interpolate mean?
Estimate a value within the range of known data.
What does extrapolate mean?
Estimate a value outside the range of known data.
What does density measure?
How much mass is contained in a given volume.
What is the formula for density?
D = m ÷ V.
What is the formula for mass using density?
m = D × V.
What is the formula for volume using density?
V = m ÷ D.
What is a common unit for density of liquids?
g/mL.
What is a common unit for density of solids?
g/cm³.
What is the SI unit for density?
kg/m³.
How are mL and cm³ related?
1 mL = 1 cm³.
What is a unit multiplier?
A conversion factor used to change one unit into another.
How do you convert 500 mL to L?
500 mL × (1 L/1000 mL) = 0.500 L.
How do you convert 2.5 kg to g?
2.5 kg × (1000 g/1 kg) = 2500 g.
What happens to vapour pressure when temperature decreases?
Vapour pressure decreases.
What happens to particle kinetic energy during cooling?
Average kinetic energy decreases.
What happens to particle kinetic energy during heating?
Average kinetic energy increases.
Which has stronger IMFs: a high-volatility or low-volatility substance?
A low-volatility substance.
Which has higher vapour pressure: strong or weak IMFs?
Weak IMFs have higher vapour pressure.
Which has a higher boiling point: strong or weak IMFs?
Strong IMFs have a higher boiling point.
Which phase change is solid → gas?
Sublimation.
Which phase change is gas → solid?
Deposition.
Which phase change is liquid → gas?
Evaporation/vaporization.
Which phase change is gas → liquid?
Condensation.
Which phase change is solid → liquid?
Melting.
Which phase change is liquid → solid?
Freezing/solidification.
What is the key relationship between temperature and average kinetic energy?
Higher temperature means higher average kinetic energy.
What is the key relationship between temperature and vapour pressure?
Higher temperature means higher vapour pressure.
What is the key relationship between IMF strength and volatility?
Stronger IMFs mean lower volatility.
What is the key relationship between IMF strength and vapour pressure?
Stronger IMFs mean lower vapour pressure.
What is the key relationship between IMF strength and boiling point?
Stronger IMFs mean higher boiling point.