chp3 ΣΤΑΘΕΡΟΤΗΤΑ ΦΑΡΜΑΚΟΥ ΚΑΙ XHMIKH KINHTIKH

Question 1

how is the ταχύτητα (ρυθμός) της χημικής αντίδρασης calculated

Answer 1

= -1/a x Δ[A]/ Δt
= -1/b x Δ[B]/ Δt
= 1/c x Δ[C]/ Δt
= 1/d x Δ[D]/ Δt

Question 2

how to get the στιγμιαία ταχύτητα μιας αντίδρασης

Answer 2

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.

Question 3

define ταχύτητες αντιδράσεις

Answer 3

= the increase of the product concentration per unit of time
= the decrease of the reactant conc per unit of time

Question 4

what is the αρχική ταχύτητα

Answer 4

= η στιγμιαία ταχύτητα στην αρχή μιας αντίδρασης (t = 0 s)

Question 5

what are the units for rate of reaction? what else needs to be specified when referring to it?

Answer 5

= 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.

Question 6

what are other ways to write the value u of νόμος ταχύτητας αντίδρασης based on the reactants

Answer 6

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

Question 7

how is the ακριβής νόμος ταχύτητας της αντίδρασης actually calculated? name the techniques

Answer 7

Προσδιορίζεται πειραματικά μέσω συγκεκριμένων τεχνικών:

• τεχνική διακοπτόμενης ροής (interrupted flow technique)
• φωτόλυσης λάμψης (flash photolysis)
• μέθοδος ροής χημικής απόσβεσης (chemical quenching flow method)

Question 8

what is the official name of k in the rate of reaction formula + what it’s affected by + units

Answer 8

= σταθερά ταχύτητας της αντίδρασης

• Εξαρτάται από τη θερμοκρασία, αλλά όχι από τις συγκεντρώσεις των αντιδρώντων.
• Oι μονάδες του 𝑘 εξαρτώνται από το νόμο ταχύτητας.

Question 9

how is the ολική τάξη of a reaction calculated

Answer 9

το άθροισμα των επιμέρους τάξεων a + b + c +…

Question 10

is it possible for there to be αντιδράσεις με αρνητική τάξη αντίδραση?

Answer 10

yes

Question 11

can some reactions have an overall νόμο ταχύτητας μηδενικής τάξης? eg?

Answer 11

𝒖 = 𝒌
—> η διάσπαση της φωσφίνης, PH3

Question 12

what does it mean when the class of a reactant is negative

Answer 12

= as the conc of the reactant increases, the rate decreases

Question 13

name the value of k for each reaction order

Answer 13

0th —> M.s-1
1st —> s-1
2nd —> M-1 . s-1
3rd —> M-2. s-1

Question 14

what is the ολοκληρωμένος νομός της ταχύτητας αντίδραση πρώτης τάξης (integral rate equation for a first-order reaction) + why is it used

Answer 14

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.

Question 15

what are the reactions of the integral rate of equation for the 1st order reaction + how to turn it into a graph

Answer 15

= - 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

Question 16

define χρόνος ημιζωής

Answer 16

= t 1/2
= time needed for the initial concentration of a reactant to decrease to half its value

Question 17

what is the half life formula for a 1st order reaction? what does it depend on?

Answer 17

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

Question 18

how is the half life value of a 1st order different to a 2nd, 3rd etc

Answer 18

The others depend on the concentration in their formula, so therefore aren’t constant

Question 19

what is the integrated version of the rate of reaction of a 2nd order

Answer 19

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

Question 20

what’s the formula for the half life of a 2nd rate order reaction

Answer 20

= 1 / k[A]0
—> it depends on the initial concentration as well as k

Question 21

compare the graphs of 1st and 2nd order

Answer 21

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

Question 22

how to determine rate from just the conc and time of 1 reactant

Answer 22

1. Write using the conc ln[R] & 1/[R]
2. Draw the 2 graphs over the time x axis and compare

Question 23

what’s the rate equation for a μηδενική τάξεως reaction that we can use as a graph + describe the graph

Answer 23

[A] = -kt + [A]0
Downwards linear slope with a gradient = -k

Question 24

define reaction mechanism

Answer 24

μηχανίμως αντίδρασης = η σειρά των βημάτων μιας αντίδρασης που καθορίζει την οδό από τα αντιδρώντα στα προϊόντα

Question 25

what is a step called in a reaction mechanism + what does it show

Answer 25

στοιχειώδης αντίδραση/ βήμα
—> σχηματισμό ή διασπάση χημικών δεσμών

Question 26

what is the ισοσταθμισμένη εξίσωση of the reaction mechanism showing

Answer 26

It only describes the stoichiometry of the reaction, without any detail on how the reaction occurred

Question 27

what are the ενδιάμεσο αντίδρασης in a reaction mechanism

Answer 27

= 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

Question 28

what is the rate determining step in the reaction mechanism

Answer 28

It’s the slowest step which will determine the overall rate of the reaction

Question 29

what is the particle collision theory

Answer 29

A 2 molecule reaction occurs when there is σωστή κατεύθυνση, ενέργεια ενεργοποίησης και σωστό στοιχειώδες βήμα.

Question 30

According to the collision theory, what occurs to the reactants if the reaction occurred in 1 step?

Answer 30

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

Question 31

link the arrhenius equation to the collision theory

Answer 31

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

Question 32

define ενεργεια ενεργοποιηση

Answer 32

= Ea = activation energy
= ένα φράγμα δυναμική ενέργεια το οποίο πρέπει να ξεπερασετι έτσι ώστε τα αντιδρώντα να μετατραπούν σε προϊόντα

Question 33

define μεταβατική κατάσταση/ενεργοποιγμένο σύμπλοκο

Answer 33

= 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.

Question 34

where does the energy come from to form the transition state

Answer 34

from the KE at the collision

Question 35

What is Arrhenius equation that allows us to see how many particles have sufficient energy = to Ea

Answer 35

f = e^ -Ea/RT

Question 36

what are external factors that can improve/reduce the energy and allow it to reach (or not) the Ea

Answer 36

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

2. 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

Question 37

what is arrhenius equation which summarizes the importance of reaction rate as well as the collision theory? how is it written in graph form?

Answer 37

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)

Question 38

how to get the Ea from a table

Answer 38

1. calculate in the table lnk (y)
2. calculate 1/T in kelvin (x)
3. Calculate the gradient
4. m = -Ea/ R —> m x R = -Ea