Lecture 13.1- Gases

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•Homework is now classwork.

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GRADING50% tests15% lab/activity10% classwork5% bellwork10% participation 10% lecture notes (stamped before lecture)

Chapter 13- States of MatterSection 13.1- Gases

The skunk releases its spray! Within seconds you smell that all-too-familiar foul odor.

You will discover some general characteristics of gases that help explain

how odors travel through the air, even on a

windless day.

The Kinetic Molecular Theory explains the behavior of gases

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The word kinetic refers to motion.

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

•According to the kinetic theory, all matter consists of tiny particles that are in constant motion.

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According to Kinetic Molecular Theory:

•The particles in a gas are considered to be small, hard spheres with an insignificant volume.

•The motion of gas particles is rapid, constant, and random.

•All collisions between gas particles are perfectly elastic.

Gas particles are in rapid, constant motion.

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Gas particles travel in straight-line paths.

Gas particles move randomly.

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A gas fills its container.

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Kinetic theory explains gas pressure.13.1

Pressure = Force/Area

A force is a push or a pull.

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more area

less area

more pressure!

Same force

Which would you prefer? Why?

Gas pressure is the force exerted by gas particles hitting the surface of an object.

•An empty space with no particles and no pressure is called a vacuum.

Gas pressure is the result of billions of rapidly moving gas particles colliding with an object.

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Atmospheric pressure is the pressure created by the earth’s gravitational pull on the gases in our atmosphere.

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

An empty water bottle, closed tightly at high elevation,

will be crushed by the atmosphere at sea level.

Pressure Poem

Units of Pressure

•The SI unit of pressure is the pascal (Pa).

•One standard atmosphere (atm) is the atmospheric pressure at sea level.

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450 kPa x kPaatm 1

101.3

450 kPa xkPa

760 101.3

mm Hg

= 4.4 atm

= 3400mm Hg

for Sample Problem 13.1

Particles at a given temperature have a wide range of kinetic energies.

Most of the particles have kinetic energies in the middle of this range.

Temperature measures Average Kinetic Energy

Absolute zero (0 K, or –273.15°C) is the temperature at which the motion of particles theoretically stops.

•Particles would have no kinetic energy at absolute zero.

•Absolute zero has never been produced in the laboratory (and not for lack of trying!).

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In this vacuum chamber, scientists cooled sodium vapor to nearly absolute zero.

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The Kelvin temperature of a substance is directly proportional to the average kinetic energy of the particles of the substance.

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The higher the kinetic energy, the higher the temperature.

Two substances with the same average kinetic energy are at the same temperature.

Two substances at the same temperature have the same average kinetic energy.

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Observe particles in motion and discover the connection between temperature and kinetic energy.

1. According to the kinetic theory, the particles in a gas

a. are attracted to each other.

b. are in constant random motion.

c. have the same kinetic energy.

d. have a significant volume.

2. The pressure a gas exerts on another object is caused by

a. the physical size of the gas particles.

b. collisions between gas particles and the object.

c. collisions between gas particles.

d. the chemical composition of the gas.

3. The average kinetic energy of the particles in a substance is directly proportional to the

a. Fahrenheit temperature.

b. Kelvin temperature.

c. molar mass of the substance.

d. Celsius temperature.