Unit 5: (d) Ideal Gas Molecules

What is the key idea of the kinetic model of gases?

A gas is made of tiny molecules moving in constant random motion.

How do gas molecules move?

In constant random motion in all directions.

Why do gases produce pressure?

Gas molecules collide with the walls of their container.

What causes pressure in a gas?

Molecules colliding with the walls of their container.

What happens during each collision between a gas molecule and the container wall?

It exerts a force on the wall.

Why do many molecular collisions create pressure?

The combined forces of many collisions produce pressure.

What is the exam definition of pressure in a gas?

Pressure is caused by molecules colliding with the walls of their container.

What is absolute zero?

The lowest possible temperature.

What is absolute zero in Celsius?

−273°C.

What is absolute zero in Kelvin?

0 K.

What happens to molecular kinetic energy at absolute zero?

It is at its minimum possible value.

What happens to the average speed of molecules at absolute zero?

It is as low as possible.

Can temperature go below 0 K?

No.

What is the exam definition of absolute zero?

The temperature at which particles have minimum kinetic energy.

What is the SI unit of temperature?

Kelvin (K).

Why does the Kelvin scale never have negative values?

It starts at absolute zero.

Where does the Kelvin scale begin?

0 K (absolute zero).

How do you convert Celsius to Kelvin?

K = °C + 273.

How do you convert Kelvin to Celsius?

°C = K − 273.

What is 0°C in Kelvin?

273 K.

What is 25°C in Kelvin?

298 K.

What is 100°C in Kelvin?

373 K.

What is −273°C in Kelvin?

0 K.

What must you do before using gas equations with temperature?

Convert Celsius to Kelvin.

What happens to gas molecules when temperature increases?

They gain kinetic energy and move faster.

Why does heating a gas increase molecular speed?

Heating gives molecules more kinetic energy.

What happens to the frequency of collisions when temperature increases?

Collisions happen more often.

What happens to the force of collisions when temperature increases?

Collisions become harder and exert greater force.

How does average molecular speed change as temperature increases?

It increases.

What is the relationship between temperature and average molecular speed?

Higher temperature gives higher average molecular speed.

What is directly proportional to Kelvin temperature?

The average kinetic energy of gas molecules.

What is the correct proportional relationship to state in exams?

Kelvin temperature is directly proportional to average kinetic energy.

What should you NOT say about temperature and speed?

Do not say temperature is proportional to speed.

What happens to pressure if volume decreases at constant temperature?

Pressure increases.

Why does decreasing volume increase pressure?

Molecules have less space so collisions are more frequent.

What law describes the pressure–volume relationship at constant temperature?

Boyle's Law.

What is the relationship between pressure and volume at constant temperature?

Pressure is inversely proportional to volume.

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

Pressure halves.

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

Pressure doubles.

What happens to pressure when Kelvin temperature increases at constant volume?

Pressure increases.

Why does pressure increase at constant volume when temperature rises?

Molecules move faster and collide harder and more frequently.

What is the relationship between pressure and Kelvin temperature at constant volume?

Pressure is directly proportional to Kelvin temperature.

Which temperature scale must be used in pressure–temperature calculations?

Kelvin.

What is the pressure–temperature equation?

p₁/T₁ = p₂/T₂.

State the pressure–temperature equation in words.

Initial pressure divided by initial Kelvin temperature equals final pressure divided by final Kelvin temperature.

How do you calculate final pressure using the pressure–temperature law?

p₂ = (p₁ × T₂) ÷ T₁.

How do you calculate final temperature using the pressure–temperature law?

T₂ = (p₂ × T₁) ÷ p₁.

A gas is heated from 300 K to 450 K at constant volume. Pressure is initially 100 kPa. What is the final pressure?

150 kPa.

What remains constant in the pressure–temperature law?

Volume.

What is Boyle's Law equation?

p₁V₁ = p₂V₂.

State Boyle's Law in words.

Initial pressure × initial volume = final pressure × final volume.

How do you calculate final pressure using Boyle's Law?

p₂ = (p₁ × V₁) ÷ V₂.

How do you calculate final volume using Boyle's Law?

V₂ = (p₁ × V₁) ÷ p₂.

A gas has pressure 200 Pa and volume 6 m³. The volume decreases to 3 m³. What is the new pressure?

400 Pa.

Why does pressure double when volume halves?

Pressure is inversely proportional to volume.

What stays constant in Boyle's Law?

Temperature.

What stays constant in the pressure–temperature law?

Volume.

What is the relationship between pressure and volume?

Inverse proportionality.

What is the relationship between pressure and Kelvin temperature?

Direct proportionality.

In a direct relationship, what happens if one quantity doubles?

The other doubles.

In an inverse relationship, what happens if one quantity doubles?

The other halves.

What is the most common gas equation exam trap involving temperature?

Using Celsius instead of Kelvin.

What is another common exam trap about gas pressure?

Pressure is caused by collisions, not continuous pushing.

When can Boyle's Law be used?

Only when temperature remains constant.

When can the pressure–temperature law be used?

Only when volume remains constant.

What happens to average kinetic energy when Kelvin temperature increases?

It increases.

What happens to molecular motion as a gas is heated?

Molecules move faster in constant random motion.

What happens to pressure if molecules collide more frequently and with greater force?

Pressure increases.