Chemistry AP Review

Thermal heat equilibrium

When hot and cold molecules collide, they create an average of the two to form a temperature (or new one)

Heat capacity

Amt of heat needed to raise temp of thing by 1 C “specific” = g “molar” = 1 mole

Q = mcΔT

Allows one to calculate heat transfer (amount of heat transferred or amount needed to make a specific change). Q = joules total m = mass C = specific heat of substance. and Delta T is the change in temp

Lower specific heat value…

Higher change in temperature

What is ΔH?

The change in heat (enthalpy).

What is enthalpy?

Heat at constant pressure

What is the delta H (change in heat) of a reverse reaction?

Flip the sign of the initial

What is constant during phase change?

Temperature (plateau)

Entropy (disorganization)

Measure of how spread out atoms and molecules become during chemical processes

Calculating enthalpy

Delta H reaction = products - reactants

How do we calculate entropy?

Delta S = final - initial

Gibbs Free Energy

G = spontaneity H = enthalpy T = Kelvin S = Entropy

High heat capacity means…

Less temperature change when exposed to heat

What comes out of the q=Mc^T?

Joules! (For Q)

How to find Q with Delta H?

Take the stoichiometry of the limiting reactant to the reaction (always 1) and cancel out to Kj

How to find qRxn in a calorimeter

Take the Q and make it negative (one gains, other loses)

How to find Delta H rxn?

The Qrxn divided by moles of the reaction, found through the limiting reactant (these being divided by the stoichiometry)

What does Delta H rxn tell us?

The energy per mole released in the reaction

What does reversing the equation do for Delta H?

Change its sign

For Delta H, what can we do when we change the stoichiometry?

Multiply Delta H by the new ratio. Double is 2x, ½ is 0.5x

How do we calculate the Delta H from several equations?

ADD, not multiply, their Delta Hs together

How to calculate Delta H from bonds

Reactants enthalpy minus products enthalpy

Delta S, positive and negative

Positive = More entropy (less order)
Negative = Less entropy (more order)

What’s a good way to gauge if entropy increased?

More moles, more gases and liquids (more entropy)

Delta H from Hf

Products minus reactants

How can we find the equivalence point on a titration curve?

The middle of the middle curve

What is the half equivalence point?

A weak acid and its conjugate base are equal at half the volume used to achieve the equivalence point (pH = pKa)

What are the strong acids to remember?

HCI, HBr, HI, HCIO4, H2SO4, HNO3

What is Ka/pKa?

The equilibrium of an acid. Pka is the -log of that

What occurs at the half equivalence point?

pH = pKa

pH = pKa + -log (A)/(HA)

Henderson-Hasselbach

What are the strong bases?

Mostly Group 1 and 2 metal hydroxides

How are pOH/pH correlated to OH/H?

Inversely

How can we find pOH or pH?

14 = pOH + pH

What is pOH/pH?

-log (OH) / -log (H)

How can we use pOH/pH to find H/OH?

They are equal to 10 to the power of the negative pOH/pH

What is LeChatelier’s principle?

If stress is put on an equilibrium equation, it will act to balance it out that stress.

If K is greater than 1, what does this mean?

Products are favored, and vice versa.

What do we never use in K?

Solids, nor aqueous solutions if not Keq.

What goes on top of K?

Products. Reactants on the bottom. Remember exponents!

What is Hess’s law?

Energy change will be the same if a reaction happens in one or multiple steps.

What are we trying to do when using Hess’s law for calculations?

To cancel out what we don’t want from a mixture of reactions.

How do we cancel out in Hess’s law?

We arrange an element on the products and reactants, and they subtract from each other. Remember that this may be necessary if you have too much of something in the final equation, in which case 2 H - 1.5 H = .5 H

What is molar solubility?

It’s molarity of a substance at equilibrium, and not the same as K.

Common ion effect

The solubility of an IONIC compound is decreased by the presence of a common ion (an ion that is also present!! in the compound).

ΔH and Endo/Exothermic

Positive is endo, negative is exo

Endothermic

Takes in heat

Exothermic

Releases heat

What do the coefficients in equilibrium reactions tell us?

The coefficients in equilibrium reactions show stoichiometric ratios/consumption. For example, X can be greater than 2Y at equilibrium.

How are H+ and OH- related?

Inversely.

Hess rules for reversing and doubling (EQUILIBRIUM ONLY)

Reversing = 1/K Doubling = Squared

What is NEVER part of equilibrium/chatelier?

Gases and liquids!

How does a catalyst effect equilibrium?

It does not change anything, it only speeds up the reaction (reverse and forward).

How do solids/liquids act in equilibrium?

Beyond being present at all, they don’t affect the equilibrium constant. Adding more does nothing!

Can gases be used in Kc?

Yes, just divide their moles by the liters.

How do we calculate molar solubility?

Get the x from the Ksp. ex: [Ag][CI] = x². If we take the square root of the Ksp we get it in this scenario.

What do metals do in solution?

Something like I2 becomes I- to dissolve better

What does saturated mean?

To be at equilibrium

How do we solve common ion problems?

use a rice box to account for the additional ion

How do we solve eq problems when the top is unknown and squared but we know the bottom?

Multiply bottom by Keq

If you have the total pressure, how can Dalton’s law tell you partial PR?

The number of moles is proportional to pressure, so use that to estimate

What do you NEVER need to use in Chemistry?

Quadratic equations

What must you remember when squaring/rooting?

The x coefficient is squared or rooted too

How do we solve common ion solubility problems?

Add the additional molarity to the concentration of the ion. Set M equal to Ksp. Get x!

When is a solution acidic?

When H30 > OH-

Hess law for multiplying coefficients by n

K^n (Times ½ is sq root of K as ex)

What can we do to avoid quadratics?

Ignore x if its very small or square root both sides

What do a strong acid and strong base make net ionic?

H30(aq) + OH(aq) → 2H20 (l)

What do a weak acid and strong base make net ionic?

HA(aq) + OH(aq) → H20(l)

What do a weak base and strong acid make net ionic?

B(aq) + H30(aq) → HB-(aq) + H20(l)

What do a weak acid and weak base make net ionic?

B(aq) + H30 (aq) → HB(aq) + H20(l)

How can we determine the strongest base/acid?

Equilibrium favors the side opposite to it

What is a buffer solution?

A weak acid and its conjugate base which prevent precipitious changes in the pH (neutralizes H and/or OH)

Effective buffer range

When the pH is less than -1 or +1 the pKa

[HA] = [A]

pH = pKa

[HA] > [A]

pH < pKa

[HA] < [A]

pH > pKa

How do we determine good indicators?

Their pKa should be near the pH at the equivalence point

What can we use to find Ka or Kb if we have the other?

ka * kb = kw

A solution is only acidic if..

[H30] > [OH]

What does high electronegativity do to a base/acid?

Base weaker b/c less proton acceptance (repels), acid stronger because more proton donation (repels)

What does low electronegativity do to a base/acid?

Base stronger b/c more proton acceptance (attracts), acid weaker because less proton donation (attracts)

Hydrochloric Acid (STRONG ACID)

HCl

Hydrobromic Acid (STRONG ACID)

HBr

Hyrdroiodic Acid (STRONG ACID)

HI

Nitric Acid (STRONG ACID)

HNO₃

Perchloric Acid (STRONG ACID)

HClO₄

Sulfuric Acid (STRONG ACID)

H₂SO₄

Group 1 AND 2 metal hydroxides are…

Strong bases

2 groups around central atom

linear (180)

3 groups around central atom

trigonal planar (120)

4 groups around the central atom

tetrahedral (109.5)

5 groups around central atom

trigonal bipyramidal (90, 120)

6 groups around central atom

octahedral (90)

3 electron groups- 1 is lone pair

Trigonal planar, Bent (less than 120)

4 groups- 1 is a lone pair

tetrahedral, Trigonal Pyramidal (107)

4 groups- 2 groups are lone pairs

Tetrahedral, bent (105)

5 groups- 1 is a lone pair

Trigonal bipyramidal, Seesaw (101.5, 173.1)

5 groups- 2 groups are lone pairs

Trigonal bipyramidal, T-shaped