Test 1 (13 - 24) Flashcards
Water ion constant
You can also use it to calculate the H30^+ or OH^- in the solution.
[OH^-] = Kw / [H3O^+]
[H3O^+] = Kw / [OH^-]
How to know if a solution is acidic, basic or neutral?
How to get pH?
Acid:
- Log of [H3O^+]
=pH
Base:
- log of [OH^-]
=pOH
14 - pOH
=pH
What are indicators?
compounds that dramatically change color when the
pH of the solution changes.
frequently weak acids or weak bases, which protonated (conjugate acid form) and deprotonated (conjugate base form) forms have different colors.
Indicators, K constant and what is prevalent/dominating in which solution?
In an acidic solution the protonated form (HIn) is prevalent, wheras in a basic solutions the deprotonated form (In-) is dominating.
How pk is obtained for indicators
Indicator equilibrium shifting when H3O^+ is added and when OH^- is added
What are buffers?
A buffer solution is a solution that maintains pH by neutralizing
added acid or bases.
What is buffer capacity?
quantity (number of moles) of
strong acid or base that must be
added to change the pH of one
liter of buffer solution by one pH
unit.
What is an acidic buffer?
a weak acid (HA) and its conjugate base (A−)
What is a basic buffer?
a weak base (B) and its conjugate acid (BH+)
How to calculate pH of a acidic buffer?
How to calculate pH of a basic buffer?
Then later 14 - pOH = pH
What are electrolytes?
after dissolving in water they separate into ions that conduct electricity
What are nonelectrolytes?
dissolve in water as molecules, not as ions, their solutions do not conduct electricity.
Strong and weak electrolytes
Weak electrolytes have a dissociation degree (a) of a <0,05
Weak acids and bases
Strong electrolytes have a dissociation degree 0,3 < a <1
Salts, strong acids and bases
How can you calculate the dissociation degree (a) of electrolytes?
a = n/n0
or
a = n/n0 * 100%
n = number of moles of original solute molecules that have dissociated
n0 = number of moles of original solute molecules (total)
Electrolytes classification(with qualities)
How do you count equivalents in electrolytes?
Based on the ion charge.
1 mole of Na+ → 1 Eq
1 mole of Ca2+ → 2 Eq
1 mole of Fe3+ → 3 Eq
What is the collision theory?
A reaction takes place only when molecules collide with the
proper orientation and with sufficient energy.
Only a few actually lead to the formation of product
What is activation energy?
The minimum amount of energy
required to break the bonds between atoms of reactants and
form all new bonds.
Heat of reaction
DH (enthalpy change)
What is an exothermic reaction?
the energy of the reactants is greater than
the energy of the products. Heat is released along with the
product formation.
ΔH < 0
reactans → products + energy
What is an endothermic reaction?
the energy of the reactants is lower than the energy of the products. Heat is absorbed and used to convert the reactants to the products.
ΔH > 0
reactants + energy → products
What type of reaction is this?
Endothermic
What type of reaction is this?
Exothermic
What is reaction rate? How to calculate?
determined by measuring the amount of a
reactant used up, or the amount of a product formed, in a certain
period of time.
Reaction rate - temperature
At higher temperature the reacting molecules move faster, more
collisions occur and more colliding molecules have sufficient energy
to react and form product → the reaction rate increase.
Reaction rate - concentration
Increasing the concentration, increases the probability of a collision between reactant particles because there are more of them in the same volume and so increases the chance of a fruitful collision
forming products → the reaction rate increase.
Reaction rate - catalyst
Lowering the activation energy by catalyst is another way to
speed up a reaction. The catalyst allows more collisions of the
reactans to have sufficient energy to form products.
Order of reaction
What is elementary reaction?
single step reaction having a single
transition state and no intermediates
rate = k * [A]^a * [B]^b
Elementary reaction molecularity of the reaction
the number of atoms, ions or
molecules that must collide with one another simultaneously to
result into a chemical reaction
sum of the
molecules of the different reactants.
What is a complex reaction
a reaction with a complicated set of reaction steps.
Complex reaction
When C -> D is slow, the rest of the reactions are fast
Complex reaction - rate-determining step
A + B + C –> ABC (2 steps)
A + B –> AB (slow)
(will need 2 steps, therefore it’s slow)
AB + C –> ABC (fast)
What is thermodynamics?
the study of the interrelationships among heat, work, and the energy content of a system at equilibrium.
First law of thermodynamics
Heat Q and work W transferred into a thermodynamic system or
transferred out of a thermodynamic system do not just disappear or appear out of nowhere.
ΔU = Q + W
What is enthalpy?
the sum of a system’s internal energy (U) and the
mathematical product of its pressure (P) and volume (V)
H = U + P * V
Second law of thermodynamics
A spontaneous process is one that occurs naturally under certain
conditions (can proceed with no outside intervention)
- diffusion
- decay of radioactive isotopes
- hot metal cooling at room temperature
A nonspontaneous process will not take place unless it is “driven”
by the continual input of energy from an external source.
- heating a metal
- gas compression
Third law of thermodynamics
A perfect crystal at zero Kelvin has zero entropy.
What is enthropy (S) ?
Degree of disorder, depends on the number of microscopic states, or microstates, associated with it (in this case, the number of atoms or molecules)
ΔSuniv = ΔSsys + ΔSsurr
ΔSuniv > 0 spontaneous
ΔSuniv < 0 nonspontaneous (spontaneous in opposite direction)
ΔSuniv = 0 reversible (system is at equilibrium)
What is Gibbs free energy?
a thermodynamic quantity equal to the enthalpy (of a system or process) minus the product of the entropy and the absolute temperature.
enthalpy, temperature, and entropy:
G = H − TS
How the Gibbs energy looks for different quantities (spontaneous, non, reversible)
Standard Gibbs free energy of reaction
