Hyps Chemistry

Front 1

Meltin points vs. Polarity

Back 1

As the polarity increases, the melting points will increase.

Front 2

Separate compounds by general polarity and mp: alkanes, alkenes, and aromatic compounds

Back 2

alkanes - least polar - lowest mp
alkene - middle polar and mp
aromatic - highest mp

Front 3

Symmetry and branching do what to mp? Why?

Back 3

- Symmetry raises MP and branching lowers them.
- The more symmetrical a molecule is, the better it packs in the crystal.

Front 4

(T/F) Forces that stabilize a moclecule more in the solid than in the liquid state will cause a molecule to have a higher melting point.

Back 4

True.

Front 5

What do you do for melting point comparisons?

Back 5

1. separate the compounds by general polarity.
2. examine each grouping for trends in polarity and or molecular symmetry.

Front 6

What do you do for boiling point comparisons?

Back 6

1. Look for unusually heavy molecules.
2. Look for highly polar functional groups.
3. Look for the effect of dispersion forces.
4. Look for trends in teh symmetry of molecules.

Front 7

(T/F) Moelcular weight is one of the key determinants of bp.

Back 7

True, something extraordinarily heavy is going to be harder to boil than something that is lighter.

Front 8

How does polarity of functional groups relate to bp?

Back 8

- Higher the polarity, the higher the bp b/c they increase the attractions of molecules for each other.
- Alcohols are capable of hydrogen bonding.

Front 9

What is the strongest type of intermolecular attraction?

Back 9

Hydrogen bonding.

Front 10

(T/F) Dispersion forces are the only kind of intermolecular attractions that cause nonpolar molecules to stick together.

Back 10

True. (If the molecule is longer, therefor it'll have more opportunities to track other molecues)

Front 11

How does symmetry relate to bp?

Back 11

- A more symmetrical molecule will be more compact and thus have less effective surface area. THerefore it has less opportunities for it to engage in dispersion-type attractions with other molecules, making it a lower bp compound.
- Less symetrical ==> higher BP

Front 12

What are the two factors that affect relativing bps btw substances?

Back 12

molecular weight and intermolecular forces.

Front 13

In terms of bps, what is the most important factor?

Back 13

polarity

Front 14

Rate Law from Experimental Results strategy

Back 14

1. Write down the general form of the rate law.
2. determine the order of the reaction wrt each reactant (start with the ones where the concentrations are constant for all but one of the reagents).
3. White down the rate law with the correct orders.

Front 15

What does the rate constant k depend on?

Back 15

temperature

Front 16

Rate Law from Reaction Mechanisms

Back 16

1. Identify the slow step in the reaction and write down the rate law expression for taht step.
2.

Front 17

Exothermic system

Back 17

delta(H)<0 (?); therefore add more heat will get more of the reactants b/c you have to think of heat as a product.

Front 18

Liquids and solids are: compressible or incompressible?

Back 18

incompressible; so altering the pressure at which the reaction occurs should have no effect.

Front 19

Ionic species: what do you have to watch out for in terms of Le Chatelier's Principle?

Back 19

Ionic species can dissociate in water depending on their electrolytic strength and may result in multiples of the original concentration of solid.

Front 20

Gas: what do you have to watch out for in terms of Le Chatelier's Principle?

Back 20

an increase in pressure favors teh side of the reaction with fewer molecules of gas

Front 21

Determining the rate law from reaction mechanisms

Back 21

1. identify the slow step in the reaction and write down the rate law expression for that step.
2. If intermediates exist in the rate law from step 1, use prior steps to solve for their concentration and eliminate them from the rate law.
3. Combine constants and simplify the rate law.

Front 22

In reaction mechanisms, what is the goal?

Back 22

to eliminate the concentraiton of intermediates b/c they are usually high-energy species that exist only briefly.

Front 23

When can you use the rate law?

Back 23

for rate limiting steps and steps of the mechanisms that are in equilibrium.

Front 24

Thermodynamic stability of the product depends on what?

Back 24

On the energy of the product; NOT the activation energy.

Front 25

What determines the rate of formation?

Back 25

the difference in energy between the starting material and the top of the hump leading to each product. (activation energy)

Front 26

Is a catalyst consumed during a reaction?

Back 26

No, it speeds up a reaction (it lowers the hump).

Front 27

delta(G)=

Back 27

delta(G) = delta(H) - T * delta(S)
-mneumonic: Good Honey Tastes Sweet

Front 28

At equilibrium, what does delta(G) equal?

Back 28

0;

Front 29

What are the three equations for delta(G)?

Back 29

delta(G) = delta(H) - T delta(S) | units: kJ/mol
delta(G)_knot = -R T ln K_eq | units: kJ/mol
delta(G) = delta(G)_knot + R T ln Q | units: kJ/mol

Front 30

At equilibrium, what does Q equal to?

Back 30

K_eq

Front 31

What is the reaction quotient equation based on the following reaction:
2NO (g) + Cl2 (g) => 2NOCl (g)

Back 31

Q = [P_NOCl]^2 / ( [P_NO]^2 [P_Cl2] )

Front 32

What should you be weary of when writing the reaction quotient equation?

Back 32

Only aqueous species and gases should be considered in the equation.
- When dealing with gases, consider the concentration.
- When dealing with gases, focus on their partial pressures.

Front 33

For combustion reactions, the carbon source has the structure _______

Back 33

CxHy

Front 34

Bond dissociation energy

Back 34

energy required to break a particular type of bond in one mole of gaseous molecules.

Front 35

Hess's Law

Back 35

delta(H_rxn) = delta(H_b(reactants)) - delta(H_b(products)) = total energy input - total energy released

Front 36

Signs for bonds broken and bond formation based on bond dissocation energy

Back 36

When bonds are broken, the enthalpy is the bond dissocation energy.

When bonds are formed, its the negative of the bond dissociation energy.

Front 37

Heat of formation

Back 37

heat absorbed or released during the formation of a pure substance from the elements at a constant pressure.

Front 38

What does a negative/positive heat of formation entail?

Back 38

- negative: heat is released to form the product.
- positive: heat is required to from the product.

Front 39

Heat of formation Hess's law?

Back 39

delta(H_rxn)=delta(H_F(products))-delta(H_F(reactants))

Front 40

General equation for combustion.

Back 40

____ + O2 => CO2 + H2O

Front 41

Enthalpy is a state function, what does this mean?

Back 41

regardless of the path you take to get from the reactants to the products, the change in enthalpy will be the same.