Chapter 13 States of Matter

13.1 The Nature of Gases

Chemistry

Today we are learning to:-

1. Describe the kinetic theory of gases

2. Interpret gas pressure in terms of the kinetic theory

3. Define the relationship between the Kelvin temperature scale

and average kinetic energy

The kinetic theory states:

1. Particles of a gas are assumed to be small, hard spheres with an

insignificant volume.

2. The motion of the particles in a gas is rapid, constant, and random.

3. Collisions between particles in a gas are perfectly elastic.

The Kinetic Theory of Gases

The energy an object has because of its motion is called kinetic energy.

The kinetic theory states that all matter consists of tiny particles that are in

constant motion.

Gas Pressure

Gas pressure results from the force exerted by a gas per unit surface area of an

object.

Empty space with no particles and no pressure is called a vacuum.

Atmospheric pressure results from the collisions of atoms and molecules in air

with objects.

Gas pressure is the result of simultaneous collisions of billions of rapidly moving

particles in a gas with an object.

A barometer is a device that is used to measure atmospheric pressure.

Gas Pressure

The SI unit of pressure is the Pascal (Pa).

One standard atmosphere (atm) is the pressure required to support 760 mm

of mercury in a mercury barometer at 25°C.

Gas Pressure

13.1

Gas Pressure

13.1

Gas Pressure

for Sample Problem 13.1

1. What pressure in kilopascals and in atmospheres, does a gas exert at 385 mm

Hg?

2. The pressure at the top of mount Everest is 33.7 kPa. Is that pressure greater

than or less than 0.25 atm?

3. What pressure in mm Hg and atm, does a sample of neon gas exert at 75.0

kPa?

Gas Pressure

Kinetic Energy and Temperature

Atoms or molecules at a given temperature have

i. a wide range of kinetic energies.

ii. most have kinetic energies somewhere in the middle of this range.

Average kinetic energy is therefore used to describe motion of particles

in a substance

At a given temperature all substances have the same average kinetic

energy

Kinetic Energy and Temperature

There is a relationship between the average kinetic energy of atoms or

molecules in a sample and its temperature.

Higher kinetic energy means higher temperatures.

Average Kinetic Energy

Absolute zero (0 K, or –273°C) is the temperature at which the motion of

particles theoretically ceases.

Particles would have no kinetic energy at absolute zero.

Absolute zero has never been produced in the laboratory.

0K = -273°C

The temperature in Kelvin of a

substance is directly proportional to the

average kinetic energy of the particles

of the substance.

13.1 Section Quiz.

1.According to the kinetic theory, the particles in a gas • are attracted to each other.• are in constant random motion.• have the same kinetic energy.• have a significant volume.

13.1 Section Quiz.

2. The pressure a gas exerts on another object is caused by • the physical size of the gas particles.• collisions between gas particles and the

object.• collisions between gas particles.• the chemical composition of the gas.

13.1 Section Quiz.

3. The average kinetic energy of the particles in a substance is directly proportional to the• Fahrenheit temperature.• Kelvin temperature.• molar mass of the substance.• Celsius temperature.

END OF SHOW