Chem 103 Exam 4

Describe the structure of ionic compounds

3 dimension crystal lattice structure with positively charged and negative charged ions held together.

What determines the force of attraction in ionic compounds

Higher charge and smaller ions both result in stronger attractions. Stronger attraction= greater lattice energy

Does forming ion-ion interactions absorb or release energy?

Energy is released when and ionic lattice forms in the gas phase (lattice energy)

Why do ionic compounds have high boiling points

It takes a lot of energy to overcome the attractions between the opposite charges in lattice

Why do ionic compounds have a hard and brittle structure

The ions are stuck together making it hard, its brittle bc when forces make the layers move the shift of like charges near one another can cause shattering.

Explain the conductivity of ionic compounds

Not conductive in solids bc ions cannot move, but in melted or aqueous states ions are free to move and carry an electric current

Relationship and difference between temp, KE, and thermal energy

Temp=avg KE of particles and is not dependent upon the number of particles. Thermal energy= Total KE of all particles so it’s dependent upon the # of particles. (inc in particles=inc in TE)

Why do particles move w/a range of diff velocities at a given temp

Particle collisions transfer energy at random so there’s a range of speeds

Boltzmans distribution

Lower temp = Lower avg particle velocity = higher # of particles at lower speeds, resulting in a tall, narrow graph.

Higher temp=Higher average particle velocity = fewer particles moving at the same speeds = spread out distribution

Properties of ideal gases

Particles have no volume, exert no forces on each other, and KE is unchanged when gases collide with each other or the surroundings

Boyles law

At a constant temp, volume and pressure have an inverse relationship

Charles law

At a constant pressure volume and temp have a direct relationship

Avogadros law

At a constant temp and pressure moles and volume have a direct relationship

Ideal gas law

PV=nRT (t is in kevlins)

Open system

can transfer energy and matter (biological systems)

Closed system

Can transfer energy but not matter (container)

Isolated system

No transfer of energy or matter

sign of Energy out of a system into surroundings

negative

sign of energy into system from surroundings

positive

Thermal energy

molecular KE

Molecular motion in solid state

Free Vibration

Molecular motion in liquid state

Free vibration, restricted rotation and translation

Molecular motion in gas state

free vibration, translation and rotation

Exothermic

Energy is released from the system into the surroundings

Endothermic

Energy is absorbed into the system from the surroundings

Heat (q)

The amount of energy that flows spontaneously from a hotter system to a colder system

First law of thermodynamics

energy cannot be created or destroyed only transformed or transferred

Sign of q when interactions are broken

Energy is input so q>0

Sign of q of the system when interactions are broken

Energy is released so q<0

Enthalpy

The way in which energy flows as heat under conditions of constant pressure

Solid-fusion-vaporization-gas

Endothermic (sublimation)

gas-condensation-crystalization-solid

Exothermic (deposition)

Explain relative magnitudes of heats for phase changes

stronger imfs= higher hvap and hfusion but hvap is always higher than hfusion bc fusion is a phase change while in vap imfs are fully overcome.

Heat capacity

How much energy is needed to inc the temp of a substance.

Relationship between heat capacity and thermal energy

Higher heat capacity=more thermal energy to inc temp (less steep slope)

Lower heat capacity=less thermal energy to inc temp (steeper slope)

Relationship between mass and heat capacity and imfs and heat capacity

Greater mass=greater heat capacity (greater mass=more particles thus more energy needed)

Stronger imfs=higher heat capacity

Formula to find the amount of heat energy required to change temp

q=mCT (Celsius for T) (c=heat capacity) (m=mass)

Why doesn’t the temperature change during a phase change

That energy is being used to break or form imfs instead of inc KE.

Explain the difference between slopes in a heating or cooling curve

Liquid has a higher heat capacity than gas meaning it requires more energy to inc the temp so the slope isnt as steep (imfs are stronger in liquid than in gas)

Why does it take more energy to boil water compared to melting

Imfs aren’t fully overcome in melting

Explain why water has a high MP/BP

Strong h-bonds require a lot of energy to overcome

Explain why water has lower density (ice floating in water)

In ice h-bonds form a open spread out structure where the molecules are further apart making it less dense

Explain why water has a high heat capacity

It takes a lot of energy to overcome the H-bonds

Explain why water has high Hvap

All h-bonds must be broken to turn into vapor which takes a lot of energy

Interactions as they pertains to solutes and solvents prior to solution

Solute: ion-ion interactions, Solvent(H2O): h-bonds, dipole-dipole, and LDFS

Interactions as it pertains to solute and solvents after the solution

Ion-dipole interactions between the solute and solvent

Process of dissolution as it pertains to enthalpy

1.) Interaction between solutes are overcome- endothermic

2.) Some interactions between solvents are overcome- endothermic

3.) New interactions between solute and solvent are formed- exothermic

What does it mean if the the temp inc when a solution formed

The new solute-solvent interactions release more energy than it took to break the og solutions (exothermic)

What does it mean if the temp dec when a solution is formed

The energy required to break to solute-solvent interactions is greater than the energy required when forming them. (endothermic)

Define a chemical change and its evidence

A change to the molecular structure resulting in the rearrangement of atoms to form new substances, which results from bonds being broken and new ones forming.

Evidence: color change, energy absorbed or released, new compound w/diff properties, gas or precipitate

Define a phase change and its evidence

Physical transformation that doesn’t alter the molecular structure

Evidence: substance is the same in all states of matter, temperature doesn’t change in a phase change, energy isn’t released or absorbed to overcome imfs between molecules

Entropy

A measure of disorder within a system that signifies the dispersion of energy (more dispersion=more thermodynamically stable)

Key things about entropy

s>gas>liquid>solid,

temp inc=entropy inc,

heavier atoms= higher entropy at a given temp

Inc in #of moles in molecules=inc in entropy

Entropy of a mixture of 2 or more types of particles is > than that of a pure substance

Spontaneous process

Physical(chemical process) which results in a lower more stable energy state

2nd law of thermodynamics

For any process to be spontaneous entropy of the universe must inc. Stotal=Ssystem+Ssurroundings

When is a reaction always spontaneous

A reaction is always spontaneous if its exothermic and has an inc in entropy of the system. (exothermic processes lower the energy of the system)

Equation for spontaneity

G=H-TS when g<0 it’s spontaneous when g>0 it is not spontaneous.

How can you determine ionic radius from a potential energy (PE) graph?

The x-value at the minimum of the PE curve represents the distance between ions. A larger x-value (further from 0) indicates a greater distance between the ions, meaning the ions have larger radii.

How can you determine the boiling point of salts from a PE graph?

A more negative potential energy minimum means stronger attractions between ions (greater lattice energy), making the salt more stable and requiring more energy to separate the ions—resulting in a higher melting/boiling point.

Process of determining the final temp of a solution

1. Convert solute to moles

2. Use q=moles*h to find q and convert to J if necessary

3. Find total mass

4. Use q=mct to find t

5. Solve for final temp: finaltemp=intital temp+t

At a constant volume explain why more molecules results in higher pressure and vise versa

More molecules result in more collisions with the walls inc the pressure, less molecules=less collisions, dec the pressure

How do gas molecules behave when they occupy more volume

More volume allows the molecules to be more spread out resulting in less collisions

How do gas molecules behave when they occupy less volume

Less volume = molecules packed tighter, so more collisions