chp3 ΣΤΑΘΕΡΟΤΗΤΑ ΦΑΡΜΑΚΟΥ ΚΑΙ XHMIKH KINHTIKH Flashcards
how is the ταχύτητα (ρυθμός) της χημικής αντίδρασης calculated
= -1/a x Δ[A]/ Δt
= -1/b x Δ[B]/ Δt
= 1/c x Δ[C]/ Δt
= 1/d x Δ[D]/ Δt
how to get the στιγμιαία ταχύτητα μιας αντίδρασης
By drawing a tangent on either the reactant or product slope on a conc/time graph.
—> if the value is negative due to a decrease in conc the negative sign is ignored for easy comparison with other values.
define ταχύτητες αντιδράσεις
= the increase of the product concentration per unit of time
= the decrease of the reactant conc per unit of time
what is the αρχική ταχύτητα
= η στιγμιαία ταχύτητα στην αρχή μιας αντίδρασης (t = 0 s)
what are the units for rate of reaction? what else needs to be specified when referring to it?
= M/s (mole per second)
—> the specific time this measure was taken needs to be written because as time passes the rate will decrease due to lack of available reactants.
what are other ways to write the value u of νόμος ταχύτητας αντίδρασης based on the reactants
based on concentration = k [A]^a x [B]^b
based on pressure = u = kp PA^a x PB^b
—> k is calculated based on the values or given
—> the bigger the power (= τάξεις αντίδρασης) , the more effect the reactant has on the rate of reaction
—> ONLY includes g or aq
how is the ακριβής νόμος ταχύτητας της αντίδρασης actually calculated? name the techniques
Προσδιορίζεται πειραματικά μέσω συγκεκριμένων τεχνικών:
- τεχνική διακοπτόμενης ροής (interrupted flow technique)
- φωτόλυσης λάμψης (flash photolysis)
- μέθοδος ροής χημικής απόσβεσης (chemical quenching flow method)
what is the official name of k in the rate of reaction formula + what it’s affected by + units
= σταθερά ταχύτητας της αντίδρασης
- Εξαρτάται από τη θερμοκρασία, αλλά όχι από τις συγκεντρώσεις των αντιδρώντων.
- Oι μονάδες του 𝑘 εξαρτώνται από το νόμο ταχύτητας.
how is the ολική τάξη of a reaction calculated
το άθροισμα των επιμέρους τάξεων a + b + c +…
is it possible for there to be αντιδράσεις με αρνητική τάξη αντίδραση?
yes
can some reactions have an overall νόμο ταχύτητας μηδενικής τάξης? eg?
𝒖 = 𝒌
—> η διάσπαση της φωσφίνης, PH3
what does it mean when the class of a reactant is negative
= as the conc of the reactant increases, the rate decreases
name the value of k for each reaction order
0th —> M.s-1
1st —> s-1
2nd —> M-1 . s-1
3rd —> M-2. s-1
what is the ολοκληρωμένος νομός της ταχύτητας αντίδραση πρώτης τάξης (integral rate equation for a first-order reaction) + why is it used
It shows the concentration of the 1 reactant at any time if we know its initial concentration [A]0 and K.
—> It’s used to analyse and predict the progress of a 1st order reaction over time. For example, to calculate how long it would take for the initial concentration to reduce to a specific value.
what are the reactions of the integral rate of equation for the 1st order reaction + how to turn it into a graph
= - d [A]/ dt = k [A]
= ln ([A]t / [A]0)
for a linear graph form:
ln [A]t = (-k)xt + ln[A]0
y= ln [A]t
m = -k
x = t
b = ln[A]0
define χρόνος ημιζωής
= t 1/2
= time needed for the initial concentration of a reactant to decrease to half its value
what is the half life formula for a 1st order reaction? what does it depend on?
Based on the previous formula which states:
= ln ( [A]t /[A]0 ) = -kt
So because the value of [A]t /[A]0 = 1/2
—> ln 1/2 = -kt 1/2 —> t 1/2 = 0.693/k
Therefore concentration doesn’t play a role for 1st order reactions, it only depends on the k value therefore the t1/2 of the reaction will stay constant
how is the half life value of a 1st order different to a 2nd, 3rd etc
The others depend on the concentration in their formula, so therefore aren’t constant
what is the integrated version of the rate of reaction of a 2nd order
1/[A]t = kt + 1/ [A]0
—> It shows that as time progresses (t increases), the concentration of the reactant decreases, and it depends on both the rate constant k and the initial conc [A]0.
—-> 1/[A]t is inversely proportional to the concentration, so it becomes larger as the concentration of reactant decreases over time.
—> this gives you a straight line graph
what’s the formula for the half life of a 2nd rate order reaction
= 1 / k[A]0
—> it depends on the initial concentration as well as k
compare the graphs of 1st and 2nd order
1st order:
- conc/time is a bent slope downwards
- ln[A]0 over time is a straight line downwards
2nd order:
- conc/time is more bent and flat at the end downwards
- 1/[A] is a linear graph upwards
how to determine rate from just the conc and time of 1 reactant
- Write using the conc ln[R] & 1/[R]
- Draw the 2 graphs over the time x axis and compare
what’s the rate equation for a μηδενική τάξεως reaction that we can use as a graph + describe the graph
[A] = -kt + [A]0
Downwards linear slope with a gradient = -k
define reaction mechanism
μηχανίμως αντίδρασης = η σειρά των βημάτων μιας αντίδρασης που καθορίζει την οδό από τα αντιδρώντα στα προϊόντα
what is a step called in a reaction mechanism + what does it show
στοιχειώδης αντίδραση/ βήμα
—> σχηματισμό ή διασπάση χημικών δεσμών
what is the ισοσταθμισμένη εξίσωση of the reaction mechanism showing
It only describes the stoichiometry of the reaction, without any detail on how the reaction occurred
what are the ενδιάμεσο αντίδρασης in a reaction mechanism
= a compound which is produced at one of the stages of the reaction and then καταναλώνεται in another step, they aren’t written in the final equation
what is the rate determining step in the reaction mechanism
It’s the slowest step which will determine the overall rate of the reaction
what is the particle collision theory
A 2 molecule reaction occurs when there is σωστή κατεύθυνση, ενέργεια ενεργοποίησης και σωστό στοιχειώδες βήμα.
According to the collision theory, what occurs to the reactants if the reaction occurred in 1 step?
The electronic configuration around all the nucleus’ to change during the collision, both forming and breaking bonds simultaneously.
Μεταξύ των σταδίων από τα αντιδρώντα έως τα προϊόντα, οι πυρήνες λαμβάνουν διάταξη έτσι ώστε όλα τα άτομα να συνδέονται ασθενώς μεταξύ τους
link the arrhenius equation to the collision theory
If the atoms have unfilled electron shells, or electron shells with low energy they are more likely to participate due to atoms tendency to need to have a full outer shell of electron.
When the collision happens, it needs to be strong enough to overcome the repulsion from the different charges, which comes from the KE during the collision
define ενεργεια ενεργοποιηση
= Ea = activation energy
= ένα φράγμα δυναμική ενέργεια το οποίο πρέπει να ξεπερασετι έτσι ώστε τα αντιδρώντα να μετατραπούν σε προϊόντα
define μεταβατική κατάσταση/ενεργοποιγμένο σύμπλοκο
= η διάταξη των ατόμων στο μέγιστο του προφίλ της δυναμικής ενέργειας
—> At the transition state, the reactant molecules have reached their highest potential energy during the reaction, and they are in a state of transition between the initial reactants and the final products.
where does the energy come from to form the transition state
from the KE at the collision
What is Arrhenius equation that allows us to see how many particles have sufficient energy = to Ea
f = e^ -Ea/RT
what are external factors that can improve/reduce the energy and allow it to reach (or not) the Ea
1, Temperature increase
—> Σε υψηλότερες θερμοκρασίες μεγαλύτερο κλάσμα μορίων (f) έχει ενέργεια μεγαλύτερη από την Εa με αποτέλεσμα να αυξάνεται και η ταχύτητα της αντίδρασης
- στερεοχημικός παράγοντας
this implies that the atom is at the right orientation for the collision. If this wasn’t the case, then even with sufficient energy the reaction would not occur
what is arrhenius equation which summarizes the importance of reaction rate as well as the collision theory? how is it written in graph form?
collision rate = Z[A][B]
reaction rate = p (right orientation) x f (Ea) x Z[A][B]
—> k = pfZ = pZ e^ -Ea/RT
Graph form:
k = Ae^ -Ea/RT
lnk (y) = (-Ea/R) (m).(1/T) (x) + lnA (b)
how to get the Ea from a table
- calculate in the table lnk (y)
- calculate 1/T in kelvin (x)
- Calculate the gradient
- m = -Ea/ R —> m x R = -Ea
