Rate of Reactions Test

Question 1

INCREASING REACTION RATE

Answer 1

• Rate/speed increasing with temperature, concentration, pressure and the state of sub division
• Catalysts further increase reaction rate in mixture

Question 2

COLLISION THEORY

Answer 2

➢ Individual particles of reactants MUST COLLIDE
➢ Collision energy is be EQUAL or GREATER than activation energy
➢ Reacting particles must collide with SUITABLE ORIENTATION
- Understand/explain how various factors; concentration, pressure, temperature, catalyst, state of sub division, nature of reactants affect reaction rate

Question 3

TRANSITION STATE

Answer 3

• Particles collide with sufficient energy and orientation they form a TRANSITION STATE
• Where original bonds break and new bonds form
• Exists for a short time
• When state decomposes it MAY led to formation of new products/reform to original reactants
• If state is unstable = decomposes quickly

Question 4

POTENTIAL ENERGY PROFILE

Answer 4

• Reacting particles approach, their repulsive forces between their ELECTRON CLOUDS SLOW them down (lose KE)
• Lost KE reappears as PE (increased)

Question 5

ACTIVATION ENERGY

Answer 5

• Minimum collision energy

- Is HIGHER when bonds are STRONGER or more NUMBEROUS as bonds must be first broken/rearranged

Question 6

COLLISION ENERGY AND TEMPERATURE

Answer 6

• Temperature is a measure of the average KE of particles of a substance
• Temperature increases = Average KE increases

Question 7

RR CONCENTRATION

Answer 7

• Raising concentration increases RR
• Higher concentration of reacting particles causes an increase in the rate of collisions between reacting particles = increased RR

Question 8

RR GAS PRESSURE

Answer 8

• Raising pressure by reducing volume or adding gas creates greater concentration of reacting gas molecules
• Increase in rate of collisions = increase RR

Question 9

RR TEMPERATURE

Answer 9

• Raising temperature of reagents increases RR
• Higher temperature particles have greater RR = more collisions = greater activation energy
• Greater percent of collisions are successful = increased RR

Question 10

RR STATE OF SUB DIVISION

Answer 10

• Hetero reactions involve reactants in separate phases
• In reactants reacting particles can ONLY collide at surface boundary (contact of separate phases)
• Increasing surface area = greater amount of reacting particles colliding, which results in increase rate of collisions = increase RR

Question 11

RR CATALYSTS

Answer 11

• Ability to speed up chemical reactions whilst remaining unchanged
• Transition metals (Mn, Pt, Pd, Au, Rh) show STRONG catalytic effects
• Catalysts increase RR by providing a reaction pathway with a LOWER ACTIVATION ENERGY
• Catalysts present greater percent of collisions with lower activation energy
• Greater percent of collisions successful = increased RR

Question 12

INORGANIC CATALYSTS

Answer 12

• Platinum
• Manganese Dioxide
• Metal elements or simple ionic compounds

Question 13

BIOLOGICAL CATALYSTS – ENZYEMES

Answer 13

• Tend to be SPECIFIC in reactions they catalyze and FASTER
• Have complex structure, and particular that allows specific molecule (substrate) fit onto a ‘dock’ with an active site on enzyme surface
• For this reason that particular enzyme will catalyze for a specific reason; ENZYME SPECIFCITY
• Once in place, the enzyme forms various weak intermolecular forces with the substrate – holding it in place at the active site
• While the substrate is here, bonds are easily rearranged to form new products

Question 14

CATALYSTS CONTRIBUTING TO SUSTAINABILITY (HABER BOSCH)

Answer 14

• Economic synthesis of chemical substances requires slow reactions to be sped up
• Catalysts offer a solution that is SUSTAINABLE; low energy input and minimizes environmental impact
• 90% of modern materials (from petroleum, plastics, fertilizers, pharmaceuticals) involve catalyst use
• Nitrogen base fertilisers are possible bc of the cataylitic synthesis of ammonia in the Haber-Bosch process

Question 15

FRITZ HABER

Answer 15

• German chemist
• Discovered suitable method for above reaction ‘HABER BOSCH PROCESS’
• 1905, published iron could be used to catalyse the reaction of nitrogen with hydrogen to produce ammonia

Question 16

CARL BOSCH

Answer 16

• Chemist and Engineer
• Successful in adapting Haber’s synthesis into an industrial process for the manufacture of ammonia ‘Haber-Bosch’ process
• Vital for manufacture of ammonia

Question 17

MOTOR VEHICLE CATALYTIC CONVERTER

Answer 17

• Device is fittest to the exhaust system of all new vehicles in Australia and other countries
• Operation relies on the catalytic ability of metals like platinum, palladium and rhodium to RAPIDLY convert toxic and polluting exhaust gas to harmless non toxic substances
• Exhaust gases are in contact with the catalytic surfaces inside the ‘honeycomb structure’ of the converter for around 100 – 400ms
• In short time, 90% of toxic nitrogen oxides NO(x) in exhaust are converted to harmless N(2)
• 80% of unburnt hydrocarbons, HCs and Co are converted to H20 and CoO2
• REDUCTION CATALYST (platinum, palladium) situation at the front of the converted catalyzes NO(x) and CO to N(2) and CO(2)
• OXIDATION CATALYST positioned at the back end of the converter and rapidly converts unburnt HCs and CO into H20 and CO(2)
• Both heterogeneous catalysts

Question 18

HETEROGENEOUS CATALYSTS

Answer 18

• Catalysts and reagents are in two different phases
• For these reactions to be catalyzed the reagent gas must be ABSORBED onto the catalyst surface
• Whilst in absorbed state, their bond are more easily arranged
• This is why activation energy for reaction is LOWERED when the catalyst is present
• Bonds amongst absorbed atoms and molecules rearrange to form new products that release from surface, regenerating catalyst into original unchanged form

Question 19

NANOFORM CATALYSTS

Answer 19

• Nanomaterials have very larg surface to volume ratio compared to bulk materials
• This makes cataylsts in the form of nanoparticles very attraction proposition
• Nanocataylsts to develop improved electrodes for the hydrogen oxygen fuel cell, which shows potention for low polluting energy converter in motor vehicles
• It uses electrodes in an electrochemical cell to convert H(2) and O(2) and producing electrical energy to operate
• Presently there isn’t widespread commercial use, major reason being that platinum electrodes easily becoming poisoned by carbon monoxide gas
• This gas is present in hydrogen fuel obtained from catalytic reforming of hydrocarbons
• CATALYTIC POISIONING occurs as CO attach strongly to catalyst surface
• Prevents the catalyst from interacting with H(2) and O(2) and catalyzing their conversation into H2O(l)
• A current but EXPENSIVE AND ENVIRONMENTALLY BAD solution involved removal of Co from hydrogen fuel then operating the fuel cell at high temperatures (150-220)
• These conditions reduce catalyst poisoning but isn’t efficient and uses high energy

Question 20

HABER BOSCH PROCESS

Answer 20

• The Haber Process is the reaction of nitrogen and hydrogen to produce ammonia
• The reaction of nitrogen and hydrogen is reversible; reaction can proceed in either the forward or the reverse direction
• Forward reaction is exothermic; produces heat and is favored at low temperatures
• Intermediate temp, high enough to allow the reaction to proceed at a normal rate, yet not so high as to drive the reaction in the reverse direction, is required
• Forward reaction favours high pressures because there are fewer molecules on the right side
• Iron catalyst increases RR

Question 21

ENZYMES

Answer 21

• biological catalysts
• proteins known as enzymes
• specific in reactions they catalyse
• fast acting
• complex structure
• structure allows substrate to fit onto a specific active site on the enzyme surface; why they only catalyst specific reactions ENZYME SPECIFICITY
• enzymes form weak intermolecular forces with substate to hold in place
• whilst substrate is like this; bonds are easy to rearrange - quick formation of new products
• once substrate goes under chemical changes new products disengage from enzyme surface - leaving enzyme in original form
• lock and key model

Question 22

CATALASE

Answer 22

• enzyme
• human body
• responsible for rapid catalytic decompostion of H2O2
• one of fastest acting catalysts