States of matter and gas laws

Which state has the most Kinetic Energy? Which has the least? Why?

Gases have the most KE. Solids have the least. Gas particles have more freedom of movement and higher average speeds compared to solids which have a fixed and tightly packed structure.

Why does water have a higher boiling point and melting point than the other substances?

Water has strong hydrogen bonding which requires more energy to break apart

Gases are likely to be found at a

low pressure and high temperatures.

Gases (5 things)

• have large freedom of movement

• are very spaced out

• have indefinite volume and shape

• are compressible

• collide to form gas pressure

What are the gas laws

these are mathematical relationships that can be used to predict changes to gaseous bodies

• deal with pressure (Pa), temperature (K), volume (mL), and amount (moles/n)all relate to Kinetic Theory of Gases

Is a substance more likely to be a gas at high or low pressures? Why?

Low pressure allows gas particles to move freely and experience less IMFs with other gas particles.

What is Charles’ Law?

Temperature and Volume are directly proportional

• V/T=V2/T2

• Charles V of Turkey

• when a gas is heated, the molecules gain KE causing them to move faster and collide with each other and the walls of the container more frequently and with greater force. This increased motion exerts greater pressure on the walls leading to an expansion of the gas (increase volume)

• Temperature must be in Kelvin

What is Boyles Law?

Pressure and volume are inversely proportional

• PxV=P2xV2

• Boyle has boils (lots of pressure and volume)

• the gas has more space to move around (volume up) the collisions with container are less frequent and with less force, then there is less pressure

What is Gay-Lussac’s Law?

Pressure and temperature are directly proportional

• P/T=P2/T2

• when the temperature of a gas increases the average Kinetic Energy of its molecules also increases. The molecules move faster and collide with wall of the container more frequently and with greater force. This increased motion results in an increase of pressure exerted by the gas on the walls of the container

• Temperature must be in Kelvin

What is Avogadro’s Law?

Volume and number of particles are directly proportional

• V/n=V2/n2

• Avagadro had very many moles

• Avogadro said two samples of gas at STP have the same volume and moles

What is the Combined Gas Law?

• PV/nT=P2V2/n2T2

• use this law whenever a gas is changing in some way

• just ignore the variables that don’t change

• describes the relationship among the pressure, temp and volume of an enclosed gas

What is standard temperature?

Kelvin (273)

What is standard pressure?

101.3 kPa

What is standard pressure and temperature?

STP 273K, 101.3 kPa

Info about Solids

• have a definite shape and definite volume

• have strong IMFs holding them together in a rigid structure

• Do not flow. Instead the particles vibrate in place

Info about Liquids

• have a definite volume, but do NOT have a definite shape

• have intermediate IMFs holding them together

• Can flow. Particles move and slide past one another

Info about Gases

• do NOT have a definite shape and do NOT have a definite volume

• Have weak IMFs- they are not held together at all

• Can flow. The particles move around independently from one another

Changes in State

Solid to Gas: sublimation

Gas to Solid: deposition

Solid to Liquid: melting

Liquid to Solid: freezing

Liquid to Gas: boiling

Gas to Liquid: condensing

Kinetic energy is

the energy of motion

Kinetic Theory

• kinetic energy is the energy of motion

• particles in all forms of matter are in constant motion

• the KE of a substance is direct to the temperature of the substance

• temperature is a measure of an object’s average KE

• all items at the same temperature have the same average KE

The Kelvin Scale

the unit of temp that measures the amount of KE

0K= no KE= no movement

0K=-273C

K=C+273

Assumptions of Kinetic Theory of Gases:

• gas particles are small spheres with insignificant volume

• gas particles move rapidly in constant random motion

• all collisions are perfectly elastic

• there is no attraction or repulsion between particles

Gas Pressure

the force exerted by a gas per unit of surface area

Gas pressure is caused by

millions of collisions of the gas particles with the side of the container

Manometer

measures gas pressure in closed container

Barometer

measures atmospheric pressure

Pressure SI units

Pascal (Pa)

• other units commonly used include millimeters of mercury (mmHg), atmospheres (atm) and torr

• sea level pressure is equal to: 1 atm=760 mmHg=760 torr=101.3 kPa

Vaporization is the process of

a liquid becoming a gas

• This can happen in two ways:

  • Evaporation-occurs at surface of liquid at any temperature

  • Boiling-occurs throughout liquid when the liquid reaches the BP

Evaporation

• occurs at the surface of a liquid

• the particles with enough KE to break the attractive forces holding the liquid together become a gas

• therefore, the overall kinetic energy of the liquid decrease, making evaporation a cooling process

Vapor Pressure

vapor pressure is the pressure of a gas trapped above a liquid

• property of the liquid (NOT GAS)

• in a closed container, evaporation will only proceed to a certain point

• equilibrium is then reached between evaporation and condensation

• vapor pressure increases with increasing temperature

• more evaporation=higher vapor pressure

Boiling point

• when you heat a liquid, more particles are able to leave the surface, which increases the vapor pressure

• boiling occurs when the liquid is heated high enough so that the vapor pressure equals the external pressure

• Boiling occurs throughout the liquid, not just at the surface

Because boiling occurs when the vapor pressure= atmospheric pressure, you can change the boiling point of a liquid by

changing the pressure the liquid is under

the normal boiling point is defined as the

temperature at which a liquid boils at 1 atm

Ideal gases are gases that

• have atoms that take up negligible space (small/unimportant)

• don’t have IMFs/attractions

• move randomly and have perfectly elastic collisions

R=PV/nT

most gases are considered ideal at

STP

when are gases not ideal?

at very low temperatures or very high pressures

What is the Ideal Gas Constant (R)?

the number found that the Combined Gas Law always equaled from ideal gases

Ideal Gas Law

• PV=nRT

• when you have an ideal gas (close to STP) and dont have a change of that gas, you can use the Ideal Gas Law

• relates pressure, temp, amount and volume of a gas

• Uses the ideal gas constant R

  • R= 0.0821 Latm/molK

  • R= 8.314 LkPa/molK

• The units must match those used for R (convert if needed)

  • Pressure= atmospheres (atm or kPa) 1atm/101.3kPa

  • Volume= Liters (L) 22.4L

  • Amount= moles (mol) 1m

  • Temperature= Kelvin (K) 273K

Dalton’s Law of Partial Pressures

• Ptotal=P1 + P2 + …

• when you have a mixture of gases, the total pressure of the system = the sum of partial pressures of each of the individual gases

What is Graham’s Law?

Rate of diffusion/effusion of a gas is inversely proportional to its molecular weight

• Diffusion- gas particles moving from high concentration to low concentration

• Effusion- gas particles moving from high pressure to low pressure

• heavy gases move slowly (large=slow), lighter gases move quickly (small=fast)

• depends on size of molecule

Vapor Pressure Curves

shows the relationship of a liquid’s boiling point (temperature) to its vapor pressure

• as you increase temperature, the vapor pressure of the liquid will increase

• once vapor pressure is equal to atmospheric pressure, the liquid will boil

• normal boiling point is at 1atm or 760 torr

Phase Diagrams

a graph of pressure as a function of temperature

• shows all three states of matter

• the Triple Point

• Normal melting and boiling points- at 101.3 kPa

What is the Triple Point?

the pressure and temperature at which all three states of matter exist simultaneously