Chem exam prep

strategies or concepts of remember

Instead of using approx method omit -x when:

Ksp exponent is than 10^-5 or smaller

When finding molar solubility and given Ksp

do not sub Ksp as x becuase Ksp is an endpoint. Only sub when finding Ksp.

K greater than 1

favour products

K less than 1

favours reacants

if Q is greater than Keq

reaction shifts left oppsite of sign

if Q less than 1

reaction shifts right opposite of sign

why when Q > Ksp a precipitate forms? (think of what supersaturated means)

Q > Ksp, the solution has more ions than it can hold at equilibrium. only one that will form a precipitate

second condition fro system to be at eq (not forwards and reverse needs to be the same):

2. The concentrations of reactants and products remain constant over time this means there is no net change

Why does a weak acid have a higher pH than a strong acid of the same concentration?

values vary because each weak acid has a different Ka value. A larger Ka means the acid ionizes more, producing more H⁺ and giving a lower pH. A smaller Ka means less ionization and a higher pH.

Ea reverse

is from the last point of the highest point

Ea forwards

is from the first step to the highest point

For delta H forwards

take the difference between the very start value on the left (flatline) and the very end flatline on the right.

For delta H reverse

take the value of delta H forwards and flip the sign

for a question like A hypothetical reaction has the rate law: rate = k [ A ]² [ B ]³

when asked for something like when a is doubled, put the factor in the brackets and do the exponent. (2)²

when (A)² is doubled and (B)³ is tripled

do (2)² x (3)³ = 108x

if you are trying to find reaction indeterminate from a multi step equation

the reaction intermediate are the ones you “cross out”

When doing average ROC

take the exact concentration over the time given in the equation

when doing instantaneous ROC

the tangent line ususally takes into account one point away from the point given on the question on either side, take the midpoints (between the point given at outer points) when doing you calculation

Kb constant

1.0 × 10^-14

OH=

10^-POH

(H3O) =

10^-pH

For an endothermic enthalpy diagram

products are higher

for an exothermic enthalpy diagram,

reactants are higher

Increasing the concentration of reactants speeds up the rate because

there are more particles because volume is increasing

using a powdered reactant instead of a lump will increase reaction rate because

there is more surface area

raising temp increases reaction rate because (2 reasons)

1. particles will move faster, causing more collisions

2. chances of an effective collision (enough energy and correct orientation to collide) increases (one that meets of exceeds the Ea)