[CHM 151] Unit 2 Test (Liquids & Thermochem)

Sublimation

solid to gas, skips liquid phase

Deposition

gas to solid, skips liquid phase

What does a high boiling point indicate?

strong intermolecular forces

Normal boiling point

temp at which vapor pressure is equal to 1 atm

Vapor pressure 

pressure exerted by a vapor in equilibrium with its liquid state 

What does a high vapor pressure indicate?

Low intermolecular forces W

What does a low vapor pressure indicate?

High intermolecular forces

Heat of Fusion

energy needed to change 1g of solid matter to a liquid at its normal melting point

Heat of vaporization 

energy needed to turn 1g of liquid to vapor at its normal boiling point

Intermolecular forces (IMFs)

attractive forces between individual molecules

What does a substances IMF depend on?

its physical properties

Rank IMFs from strongest to weakest 

ion-dipole, hydrogen bonding, dipole-dipole attractions, London Dispersion 

London Dispersion

temporary polarity due to unequal distributions of electrons

Which IMF does everything have?

London dispersion

Dipole-Dipole attractions

permanent polarity due to structure - EN atoms or polar molecules

How does mass affect IMFs?

the more mass an atom or molecule has, the more electrons it has which means greater IMFs

How is polarity determined?

asymmetry or presence of lone pair

Hydrogen bonding

attractions due to bonding of H with N, O, F

What happens in hydrogen bonding?

EN atom binds with H and completely destroys its electron cloud leaving a bare proton

Ion-dipole interactions 

H2O molecules surround ions to form hydration shell, aqueous liquids!

What 2 physical properties are great indicators of IMF strength?

boiling and melting point

Specific heat

energy needed for 1g of substance to change by 1C

What is the specific heat of water?

4.184 J/gC or 1 cal

Heat equation 

q=mCs\Delta T

Internal energy equation

\displaylines{\Delta E=\left(mC_{s}\Delta T\right)+\left(-P\Delta V\right)}

What is the net energy of the universe?

0

What do state functions depend on?

the reactants and products of reactions, how it got to the end product doesn’t matter!

Which variable is considered a state function? 

\Delta E

Enthalpy (H)

changes in a system’s heat in respect to pressure

Heat (q)

transfer of thermal energy between 2 bodies that causes temp differences

How does enthalpy differ in forward or reverse reactions?

The reverse of a reaction is the OPPOSITE of the forward

Standard state 

1 atm, 1M, 25C or 298K

Enthalpy of reactions

\Delta H_{rxn}=\sum\left(n\cdot\Delta H_{f}products\right)-\sum\left(n\cdot\Delta H_{f}reactants\right)

Hess’s Law

the change of enthalpy of total processes is equal to the sum of enthalpy changes of the individual processes

What is the trend of bond strength in respect to bond length? 

As bond strength increases, bond length decreases

Bond enthalpy equation

\Delta H=\sum D_{reactants}-\sum D_{products}

What happens to vapor pressure as temperature increases?

It also increases!

What is the heat of formation for pure substances/elements?

0