chem unit 3.1 kapowww

gases are not

a condensed phase

solids ___ be compressed

cannot , gases can be

density of gas is

way lower than density of liquid

the higher the pressure

the more dense the gas

the lower the temperature

the more dense the gas

characteristic of gas

Simple molecular formulas

Low molecular masses (light)

Nonmetallic elements

Rapid expansion to fill all available volume

Highly compressible

3 types of gases

monoatomic

diatomic

polyatomic

gases phase if

T (temperature) > BP (boiling point)

vapors

the gaseous state of substances that are liquids or solids under ordinary conditions

formation of homogeneous mixture

Molecules are relatively far apart

Very few interactions between gas molecules

Total Pressure Gas Mixture =

Sum of Individual Gas Pressures

Gases exert pressure on

any surface with which they are in contact

pressure (P) corresponds with

force (F) acting on an area (A)

pressure formula

p=f/a

(pa[n/m²])= (N[kgm/s²])/(m²)

standard atmospheric pressure

typical pressure at sea level - one 1atm

pressure

freq of collision of gas molecules with walls of container

4 variables to define physical condition of gas

Temperature

Pressure

Volume

Amount of gas

dalton’s law

In a mixture of non-reacting gases, the total pressure exerted is equal to the sum of the partial pressures of the individual gases

Fahrenheit to Celsius formula

f- 32 × 5/9 =c

boiling point

100 C / 373 K

freezing point

0 C/ 273.5K

absolute 0

-273 C / 0 K

Absolute-temperature scale

Kelvin scale

0 K, the absolute zero is -273.15 °C

celsius to kelvin formula

𝑇(°𝐶) + 273.15 = 𝑇(𝐾)

stp / standard conditions for gases

T= 273 K (=0C) and P = 1atm (10^5, Pa=14.7 psi

volume and pressure

inversely

temperature and volume

directly

amount of molecules and volume

directly

boyle

volume increases as pressure decreases and decreases as pressure increases

charles

volume increases as temperature increases and decreases as temperature decreases

avogadro

The volume of a gas maintained at constant temperature and pressure is directly proportional to the number of moles of the gas

gay lussac

The pressure of a gas is directly proportional to its absolute temperature when the volume is held constant

ideal gas

hypothetical gas

ideal gas law

PV = nRT

Two assumptions when dealing with ideal gases

the molecules of an ideal gas do not interact with one another

the combined volume of the molecules is much smaller than the volume the gas occupies (volume occupied by the molecule is negligible)

R

gas constant

Measured volume for given values of P, n, and T might

differ from the volume calculated from PV = nRT

as molar mass increases

behavior deviates from ideal gas

combined gas law

(P1V1)/(n1T1)=(P2V2)/(n2T2)

When a problem involves a comparison of two gases or two states (initial and final) of a single gas, us

general gas equation

else use ideal gas

molar mass equation

MM= d (or m/V) * RT/P

To find the molar mass of a substance

add the atomic masses of all the atoms in the substance. The units for molar mass are grams per mole (g/mol).

when does volume of gas increase

when external pressure decreases

dalton’s law

The total pressure of a mixture of gases equals the sum of the pressures that each would exert if it were present alone

ideal gas state

high temp, low pressure

At constant temperature and constant volume, the total pressure of a gas sample is determined by

the total number of moles of gas present, whether that total represents just one gas or a mixture of gases

mole fraction (Xi)

Xi= moles of gas i/ total moles of gas

=ni/nt

Partial pressure in terms of mole fraction and Pt

Pi=XiPt

Gas Laws

Good prediction for gas behavior

Don’t explain what’s happening on the molecular level

19th century: Physicists related gas physical properties to

the motion of individual gas molecules

Molecular movements

form of energy

Energy

work done

= Force x Distance

Kinetic energy

is a form of energy that an object or a particle has by

reason of its motion.

If work is done on an object by applying a net force,

the object speeds up and thereby gains kinetic energy

kinetic energy formula

KE= ½ mv²

The kinetic molecular theory relies on 5 assumptions:

1. Gases consist of large numbers of molecules that are in continuous, random motion.

2. The combined volume of all the molecules of the gas is negligible relative to the total volume in which the gas is contained.

3. Attractive and repulsive forces between gas molecules are negligible.

4. Energy can be transferred between molecules during collisions (Elastic

Collisions) but, as long as temperature remains constant, the average

kinetic energy of the molecules does not change with time

5. The average kinetic energy of the molecules is proportional to the

absolute temperature. At any given temperature the molecules of all

gases have the same average kinetic energy.