1. CHEMICAL KINETICS AND EQUILLLIBRIUM
prof. V. Paulauskas

2. the factors that affect this speed
Chemical kinetics – is the study of the speed with which a chemical reaction occurs
and
the factors that affect this speed
The rate of a reaction – is the speed at which a reaction happens
It is not about “how much” of a product is made, but about “how quickly” a reaction takes place
prof. V. Paulauskas

3. High rate – explosions, fuel combustion
Chemical reaction – process, when the reactants are consumed and the products are produced
The rate of reactions is very different:
High rate – explosions, fuel combustion
(quick oxidation – can happen in less than one second)
Low rate – soil formation, corrosion, respiration
(slow oxidation – take hundreds, maybe even thousands, of years)
If a reaction has a low rate, that means the molecules combine at a slower speed than a reaction with a high rate
prof. V. Paulauskas

4. Collision Theory
The collision theory says that as more collisions in a system occur, there will be more combinations of molecules bouncing into each other
If there are a higher number of collisions in a system, more combinations of molecules can occur
So reaction will go faster and the rate of that reaction will be higher
Even though they are both liquids, think about how slowly molecules move in honey when compared to your soda.
There are a lower number of collisions in the honey
prof. V. Paulauskas

5. Collision Theory
Collisions between reacting molecules are necessary before a reaction can occur
Only those collisions having sufficient energy are effective in bringing about a reaction activation energy
Colliding molecules must be properly oriented with respect to one another for the reaction to take place
prof. V. Paulauskas

6. then there are two possible ways of measuring the rate:
Reaction Rate
If we consider a reaction:
e.g. zinc + hydrochloric acid → zinc chloride + hydrogen
Zn + HCl → ZnCl2 + H2
then there are two possible ways of measuring the rate:
1) measure how quickly one of the products (e.g. H2) is made
2) measure how quickly one of the reactants (e.g. Zn) disappears
prof. V. Paulauskas

7. Reaction rate – changes in a concentration of a product or a reactant per unit time:
(mol / L .s)
Units of reaction rate – moles per litre per second
Reaction rate varies – so instanteneous rate will be concentration change in a very short time interval
(mol / L .s)
dc – product or reactant concentration changes
dτ – very short time interval
prof. V. Paulauskas

8. The four main Factors affecting reaction rate:
1 – Concentrations of reactants
2 – Temperature
3 – Catalyst being present
4 – Surface area of solid reactants
prof. V. Paulauskas

9. Comments according to the theory of COLLISION
Concentration: more molecules in a given volume translates into a greater probability of collision
prof. V. Paulauskas

10. Comments according to the theory of COLLISION
Temperature: higher temperature means that more molecules will possess the required activation energy and thus a higher proportion of collisions will be effective
prof. V. Paulauskas

11. Catalyst and Surface area:
Comments according to the theory of COLLISION
Catalyst and Surface area:
a catalyst (or crushing of solid reactants) provides a surface on which the reaction can take place. This increases the number of collisions between the particles of the substances that are reacting
prof. V. Paulauskas

12. 1. CONCENTRATION OF REACTANTS
Dependence of reaction rate upon concentration (pressure) of reactants is defined by the Law of Mass Action:
Rate of reaction is directly proportional to the product of molar concentrations of the substances reacting
If the following imaginary reaction occurs,
where reactants are A ir B, and products – C ir D:
[A], [B] – molar concentrations of reactants
m, n, p, q – stoichiometric coeficients
k – proportionality constant – called the rate constant of the reaction
prof. V. Paulauskas
Concentration: If there is more of a substance in a system, there is a greater chance that molecules will collide and speed up the rate of the reaction. If there is less of something, there will be fewer collisions and the reaction will probably happen at a slower speed. Sometimes when you are in a chemistry lab, you will add one solution to another. When you want the rate of reaction to be slower, you will add only a few drops at a time instead of the entire beaker.

13. CaO (s) + CO2 (g) → CaCO3 (s)
This Law is not valid for the solids:
2H2 (g) + O2 (g) → 2H2O (g)
1 Example:
V = k . [H2]2 . [O2]
CaO (s) + CO2 (g) → CaCO3 (s)
2 Example:
V = k . [CO2]
Stoichiometry determines the molar ratios of reactants and products in an overall chemical reaction
prof. V. Paulauskas

14. Problem: Calculate the change of reaction rate if system pressure was raised from 1Atm to 2Atm
Pressure and concentration relation:
If gas pressure is increased 2 times,
the system volume should be decreased by 2 times,
and concentration of reacting gaseous substances will increase 2 times
prof. V. Paulauskas

15. Pressure and Concentration
Pressure affects the rate of reaction, especially when you look at gases
When you increase the pressure, the molecules have less space in which they can move
That greater density of molecules (or molar concentration) increases the number of collisions
When you decrease the pressure, molecules do not hit each other as often - the lower pressure decreases the rate of reaction
prof. V. Paulauskas

16. 2. TEMPERATURE
When you raise the temperature of a system, the molecules bounce around a lot more because they have more energy
When they bounce around more, they are more likely to collide – that fact means they are also more likely to combine
When you lower the temperature, the molecules are slower and collide less – so such temperature drop lowers the rate of the reaction
prof. V. Paulauskas

17. 2. TEMPERATURE γ γ the Rule of van‘t Hoff:
Dependence of the rate of reaction upon temperature is expressed by
the Rule of van‘t Hoff:
Rate of chemical reactions is increased from twofold up to fourfould for each rise of 10°C in temperature γ
T1,2 ir VT1,T2 – temperature and reaction rate before and after the inrease
– reaction temperature coeficient (value ) γ
prof. V. Paulauskas

18. Problem: Calculate the increase of the rate of chemical reaction, if temperature was raised from 0ºC up to 100ºC, and temperature coefficient is equal to 2 , or alternatively – 3?
1 case:
2 case:
prof. V. Paulauskas

19. 3. CATALYSIS
It is possible to increase the rate of a chemical reaction by adding a substance that helps the reaction along without itself being a reactant or product. Such additives are called catalysts
The function of a catalyst is to lower the activation energy for the reaction. An additive, that has the opposite effect by slowing down a reaction, is called an inhibitor
Physical state – homogeneous and heterogeneous catalysts
A catalyst is a substance that speeds up or slows down a reaction without being used up itself
Catalysis is the increase in rate of a chemical reaction due to the participation of a substance called a catalyst
prof. V. Paulauskas

20. How does a catalyst work?
3. CATALYSIS
How does a catalyst work?
1) A catalyst provides a surface on which the reaction can take place. This increases the number of collisions between the particles of the substances that are reacting
2) A catalyst lowers the activation energy (the minimum amount of energy needed for a reaction to take place). This means that the particles can react with less energy than they needed before the catalyst was added. (Think about it: if the government lowered the legal age to buy cigarettes, then more people could legally buy cigarettes. Similarly, if we lower the amount of energy needed for particles to react, then more particles can react).
prof. V. Paulauskas

21. MECHANISM OF CATALYSIS
A + B = AB (catalyst – K)
1 stage K + A → KA (intermediate product)
2 stage KA + B → AB + K (catalyst resumes)
Total A + B + (K) → AB + (K)
Catalyst participates in the reaction, but without being used up – just forming an intermediate product
prof. V. Paulauskas

22. MECHANISM OF CATALYSIS
2SO2 + O2 → 2SO3 (catalyst – NO)
1 stage NO + O2 → 2NO2
2 stage NO2 + 2SO2 → 2SO3 + 2NO
Total O2 + 2SO2 + (2NO) → 2SO3 + (2NO)
Catalyst may participate in multiple chemical transformations
But, unlike other reagents in the chemical reaction, a catalyst is not consumed
prof. V. Paulauskas

23. CATALYTIC CONVERTER
The first widespread introduction of catalytic converters was in the US market, where 1975 model year gasoline-powered automobiles were equipped to comply with tightening US EPA regulations on exhaust emissions
A catalytic converter is a vehicle emissions control device which converts toxic byproducts of combustion in the exhaust of an internal combustion engine to less toxic substances by way of catalysed chemical reactions
prof. V. Paulauskas

24. CATALYTIC CONVERTER
Catalytic converters use metals like platinum, palladium and rhodium to convert poisonous compounds in vehicle exhausts into less harmful things. For example, a reaction which removes both carbon monoxide and an oxide of nitrogen is:
Because the exhaust gases are only in contact with the catalyst for a very short time, the reactions have to be very fast. The extremely expensive metals used as the catalyst are coated as a very thin layer onto a ceramic honeycomb structure to maximise the surface area.
prof. V. Paulauskas

25. Automobilio degimo produktai
Vidaus degimo variklis, kurio darbinis tūris 2000 cm³, per valandą išskiria apie 200 m3 degimo produktų
Susidaro 3-4 m3 degimo produktų per 1 minutę
Katalizatoriaus veikimo efektyvumas priklauso nuo jo darbinio paviršiaus ploto
Automobilio katalizatorių darbinė dalis yra smulkiai akyta, korio pavidalo – taip į mažą tūrį sutalpinama didelį paviršiaus plotą turinti aktyvioji medžiaga
(darbinis plotas prilygsta futbolo aikštei – m2)
prof. V. Paulauskas

26. Katalizatoriaus konstrukcija
Keramika, padengta kelių atomų storio katalizinių savybių turinčio metalo (platinos, rodžio ar paladžio) sluoksniu
Katalizatoriaus bendras vaizdas
Akyta korio darbinė dalis
The Platinum – Rhodium catalysts in automobile catalytic converters are heterogeneous catalysts. They provide a surface on which carbon monoxide is converted to carbon dioxide.
prof. V. Paulauskas

27. Pagrindiniai išmetamųjų dujų komponentai
Azotas (N2) - oro sudėtyje yra 78% azoto
Vandens garai (H2O) - nekenksmingas degimo produktas
Anglies dioksidas (CO2) - netoksiškas degimo produktas, bet neigiamai veikia atmosferą (sukelia "šiltnamio efektą")
Anglies monoksidas (CO) – nuodingas degimo produktas
Angliavandeniliai (CH) – įvairūs organiniai junginiai, nekokybiškai sudegusio kuro rezultatas. Atmosferoje, veikiami saulės reaguoja su azoto oksidais, sudarydami – ozoną (O3)
Azoto oksidai (NOx) – nuodingi, rūgštaus lietaus komponentai
Katalizatoriaus paskirtis – skaidyti kenksmingus aplinkai ir žmogui degimo komponentus į mažiau kenkiančius ar nepavojingus
prof. V. Paulauskas

28. CHEMICAL PROCESSES IN CC
Most present-day vehicles are fitted with a “three-way” converter, so named because it converts the three main pollutants in automobile exhaust: carbon monoxide, unburned hydrocarbon and oxides of nitrogen
The first two undergo catalytic combustion and the last is reduced back to nitrogen
Reductive catalysis: NO → N2 + O2
2NO2 → N2 + 2O2
Oxidative catalysis: CO + O2 → 2CO2
CH + O2 → CO2 + H2O
prof. V. Paulauskas

29. Katalizės sąlygos
Aukštatemperatūrinė katalizė - katalizatorius pradeda dirbti tik kai išmetimo sistema pakankamai įkaista
Esant šaltam varikliui neveikia – modernūs modeliai turi pakaitintuvus
Per aukšta – sutrumpina katalizatoriaus tarnavimo laiką
Oksidacinei katalizei reikalingas deguonis
Katalizatoriaus korpuse montuojamas lambda zondas, kuris matuoja deguonies kiekį išmetamosiose dujose
Pagal gautus duomenis elektroninis valdymo blokas reguliuoja degiojo mišinio kuro-oro santykį, taip užtikrindamas geresnį kuro sudegimą ir oksidavimui reikalingo deguonies tiekimą katalizatoriui
prof. V. Paulauskas

30. CATALYTIC CONVERTER Advantages: Disadvantages:
Kenksmingų dujų kiekio mažinimas, tuo pačiu aplinkos ir žmogaus sveikatos apsauga
Katalizatoriui nereikia jokio techninio aptarnavimo. Keičiamas po 100 tūkst. km.
Disadvantages:
Didelė kaina, nes katalizatoriui pagaminti reikia itin brangių ir retų metalų, tokių kaip platina, paladis, rodis
Automobilio galios sumažėjimas, nes deginiai, turi įveikti papildomą pasipriešinimą (3-5 % padidėja kuro sąnaudos)
Tinka tik bešvinis kuras – švino priedai iššaukia katalizatoriuje nepageidautinas reakcijas
prof. V. Paulauskas

31. 4. SURFACE AREA
Reducing the size of particles increases the rate of a reaction because it increases the surface area available for collisions to take place
This increases the number of collisions
It has no effect on the energy of the particles
prof. V. Paulauskas

32. 4. SURFACE AREA
prof. V. Paulauskas

33. 4. SURFACE AREA
The more finely divided the solid is, the faster the reaction happens. A powdered solid will normally produce a faster reaction than if the same mass is present as a single lump. The powdered solid has a greater surface area than the single lump
In the lab, powdered calcium carbonate reacts much faster with dilute hydrochloric acid than if the same mass was present as lumps of marble or limestone.
prof. V. Paulauskas
Nature of the reaction: anything about a reaction which facilitates efficient contact between the particles falls in this category; among the possibilities: surface area, fewer reactants in the balanced equation, fluid phase,

34. pvz.: mA + nB ↔ pC + qD (V1 = V2)
CHEMICAL EQUILIBRIUM
Grįžtamos reakcijos - tai tokios reakcijos, kai produktai C, D reaguoja tarpusavyje ir vėl susidaro pradinės reakcijos A, B:
pvz.: mA + nB ↔ pC + qD (V1 = V2)
Kai medžiagų koncentracija, temperatūra ir slėgis nekinta ir reakcija abiem kryptimis (tiesioginė V1 ir atgalinė V2) vyksta vienodu greičiu, tokia sistema vadinama pusiausvyraja
Tokią būseną apibūdina pusiausvyros konstanta K:
prof. V. Paulauskas

35. Pvz.: Kokia bus cheminės pusiausvyros konstantos K išraiška šiai reakcijai?
H2 + J2 ↔ 2HJ
prof. V. Paulauskas

36. CHEMINĖ PUSIAUSVYRA
Cheminė pusiausvyra esti tol, kol yra pastovios sistemos sąlygos (koncentracija, temperatūra, slėgis)
Jas pakeitus cheminė pusiausvyra sutrinka ir po kurio laiko susidaro nauja pusiausvyra, atitinkanti naujas sąlygas. Sakoma, kad pusiausvyra pasislinko tiesioginės ar atgalinės reakcijos kryptimi
Pusiausvyros poslinkio kryptį nusako La Šatelje principas:
Pakeitus vieną iš sąlygų (koncentraciją, slėgį, temperatūrą), sistemos pusiausvyra pasislenka tokia kryptimi, kad išorinių veiksnių poveikis sumažėtų
prof. V. Paulauskas

37. La Šatelje principas: IŠVADOS
Koncentracija. Padidinus, kurios nors medžiagos koncentraciją, intensyviau ima vykti ta reakcija, kurioje ta medžiaga suvartojama
Temperatūra. Didinant temperatūrą, pusiausvyra pasislenka endoterminėmis reakcijos kryptimi
Slėgis. Didinant slėgį, pusiausvyra pasislenka ta kryptimi, kur susidaro mažesnis dujinių medžiagų molekulių skaičius
Pvz.: Poslinkis į dešinę?
H = -92 kJ/mol; Q = +92 kJ/mol; (V1 – egzoterminė reakcija)
1. Didinti pradinių medžiagų koncentraciją, ir šalinti reakcijos produktus
2. Mažinti reakcijos mišinio temperatūrą
3. Didinti sistemos slėgį:
4 mol (89,6 litrai)  2 mol (44,8 litrai)
prof. V. Paulauskas

38. La Chatelje rule: shift of the chemical reaction
Example.: How to make a shift of equilibrium to the right side?
Q = +92 kJ/mol; (V1 – egzothermic reaction)
1. Increase concentration of those compounds which are participating in the reaction (concentration of reactants)
2. Lower temperature of the system (increasing makes a shift to the direction of the endothermic reaction)
3. Increase presure of the system (increasing makes a shift to the direction where the system volume is smaller):
4 mol (89,6 L)  2 mol (44,8 L)
prof. V. Paulauskas

39. Ačiū už dėmesį 
prof. V. Paulauskas