chem ch 8 quiz

gas

a substance that has neither definite volume nor definite shape.

characteristics of gasses

expand to fill their containers
are highly compressible
have extremely low densities
form homogenous mixtures
molecules in a gas are relatively far apart

vapors gaseous state of any substance that normally exists as a liquid or solid

pressure

P = F/A (force over area)

produced by gas molecules colliding with the walls of a container

determined by the frequency & force of collisions

increased pressure is due to:

more frequent collisions
higher energy

Pressure depends on:

Volume of the gas
Number of gas molecules
Temperature of the gas

How does decreasing the volume of the gas
affect its pressure?

Decreasing the volume of the gas increases its
pressure because the gas molecules are
crowded into a smaller volume and collide with
the container walls more frequently.

Pressure is proportional to ____

n (number of molecules) at constant Temp. and Volume.

How does more moles affect the pressure?

Frequency of collision increases with more moles of gas in the container.

Atmospheric pressure

The force exerted by the atmosphere on a given surface area.

Applies a force equally in all
directions
Decreases with an increase in
altitude

barometer

An instrument that measures atmospheric pressure

mm Hg to torr

1 mm Hg = 1 torr

atm to torr

1 atm = 760 torr

atm to pascal

1 atm = 101,325 Pa

the 4 variables that define the physical states of gases:

• Pressure
• Temperature
• Volume
• Number of Moles of Gas

volume and pressure relationship

Pressure and Volume are inversely proportional.

Decreasing volume causes pressure to increase, and vice-versa.

This is referred to as Boyle's Law.

volume and temp relationship

Volume and Temperature are directly proportional.

When one increases, so does the other. (As you heat something, it tends to expand.)

This is referred to as Charles's Law.

Absolute Zero

The temperature at which all motion stops
0K or -273OC

of moles and volume relationship

The number of moles of gas and the volume they occupy are directly proportional. (The more gas you have, the more space it occupies, at constant pressure and temperature.)

This is referred to as Avogadro's Law.

STP

Standard Temperature and Pressure
P = 1 atm
T = 273K
n = 1 mole

ideal gas equation

PV = nRT

P

pressure (atm)

V

volume (Liters)

n

of moles

R

gas constant (0.08206 atmL/Kmol)

T

temperature (kelvins)

grams to moles

divide by molar mass

celsius to kelvin

C+273

torr to atm

760 torr = 1 atm

how to solve gas law problems

1) Identify which of the four variables are changing.
2) Put all the "constants" on one side and the variables that are changing on the other.
3) Rewrite the equation with the variables on both sides of the equal sign. Apply subscripts of "1" to one side and "2" to the other.
4) Figure out what is given and what is needed, solve for needed.
5) PUT NUMBERS IN LAST