Chemistry 20 Unit B, Gases

properties of gases

• have neither shape nor volume of their own, and always fill their container

• highly compressible (V down if P up, vice versa)

• gases diffuse spontaneously throughout any spaces

• temperature can affect the V and P

• much lower densities than liquids and solids

Boyle’s law

• volume changes, so will pressure (if temp is constant)

• pressure is a result of the frequency of collisions between particles and container, and particle with particles

• if temperature is constant, so is the velocity of the particles

• V down, P up, vice versa

Kinetic Molecular Theory

• particles are always moving

• more energy, faster particles

• particles move randomly, (brownian motion)

three types of motion

• Vibrational: vibrating back and forth in one spott

• Rotational: spinning motion (one spot)

• Transitional: straight line motion

what types of motion do solids have

vibrational only (particles are fixed in place, not moving past each other)

what types of motion do liquids have

all three types of motion, primarily translational (particles are still densely packed, but can move past one another).

what types of motion do gases have

all three (particles a far apart and freely moving past each other).

atmospheres

an envelope of gases extending outward from the surface of a planet, held there by the gravitational forces of the planet.

atmospheric pressure

the force that a column of air exerts on the Earth’s surface at the bottom of the column.

layers of atmospheres exert pressure downwards, so…

the bottom layer will be compressed the most, so higher layers are compressed very little.

pressure

force per unit area

pressure is ______ _____ to force, meaning,

directly related, so an increase in force results in an increase in pressure

pressure is ______ _____ to surface area, meaning,

inversely proportional, so an increase in area results in a decrease in area

one atmosphere is equal to

101.325kPa

101.325 kilo-Pascals is equal to

1 atm

pascals (pressure units)

N/m², (newtons per metre squared)

1 atm is also equal to

760 mmHg

760 mmHg is equal to

one atmosphere

1 bar is equal to

100kPa

100kPa is equal to

1 bar

how to convert from celsius to kevin

add 273.15

what does R=?

8.314 (kPa x L)/(mol x K)

Boyle’s law resulting formula

P₁V₁=P₂V₂ (@ constant T and n)

Boyle’s law is useful for

closed systems

Standard Temperature and Pressure

T=273.15K, P=101.325kPa, V_m=22.4L/mol

Standard Ambient Temperature and Pressure

T= 298.15, P=100.0kPa, V_m=24.8L/mol

Charles’ Law

as the temperature of a gas increases, the volume will increase proportionally, as long as all the other variables (n, P, etc.) remain constant.

Formula From Charles’ Law

(V₁/T₁)=(V₂/T₂)

Charles’ law formula is applicable when:

P is constant, closed system, T is in kelvin

Combined Gas Law

a combination of Boyle’s law, and Charles’ law.

Combined Gas Law Formula

((P₁V₁)/T₁)=((P₂V₂)/T₂)

when to use Combined Gas Law

on a closed system that undergoes any change in P,V,T

Combining Volumes Law

when gases react, the volumes of the gaseous reactants and products occur in whole number ratios. (when measured at same conditions obv)

Avogadro’s Theory

equal volumes of gas at the same T and P, contain equal numbers of molecules.

Avogadro’s Number

6.02×10²³

Avogadro’s Law Formula

(n₁/V₁)=(n₂/V₁)

How to use Avogadro’s Law Formula

• Create and balance the chemical equation

• use n values of products/reactants with given volumes

Molar Volume (V_m)

the volume occupied by any gas at specific conditions

Using Molar Volume to find number of mol (formula)

n=V/V_m

Ideal Gases

a gas in which the molecules are assumed to exert no attraction or repulsion on each other

Ideal Gas Characteristics

• the gas molecules are in constant, random motion, travelling in straight lines.

• the molecules are considered “point masses”

• the molecules only interact with one another and the container in elastic collisions

• perfectly obey all gas laws under all conditions

• do not condense into liquids

Point Masses

masses without volume.

elastic collisions

collisions in which total kinetic is conserved. energy can be exchanged, but total energy is maintained.

Real gases

• do condense into liquids

• do have particles that attract each other

• don’t perfectly follow gas laws

Ideal Gas Law Formula

PV=nRT

Dalton’s Law of Partial Pressures

In a mixture of gases, the total pressure is the sum of all the partial pressures of each gas within. (the greater the amount of the particular gas, the greater its partial pressure will be)

Dalton’s Law of Partial Pressures Formula

Ptot=P1 + P2 + P3… (Dont really need to know!!!!!!1)