Rate of Reactions Test Flashcards
1
Q
INCREASING REACTION RATE
A
- Rate/speed increasing with temperature, concentration, pressure and the state of sub division
- Catalysts further increase reaction rate in mixture
2
Q
COLLISION THEORY
A
➢ 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
3
Q
TRANSITION STATE
A
- 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
4
Q
POTENTIAL ENERGY PROFILE
A
- Reacting particles approach, their repulsive forces between their ELECTRON CLOUDS SLOW them down (lose KE)
- Lost KE reappears as PE (increased)
5
Q
ACTIVATION ENERGY
A
- Minimum collision energy
- Is HIGHER when bonds are STRONGER or more NUMBEROUS as bonds must be first broken/rearranged
6
Q
COLLISION ENERGY AND TEMPERATURE
A
- Temperature is a measure of the average KE of particles of a substance
- Temperature increases = Average KE increases
7
Q
RR CONCENTRATION
A
- Raising concentration increases RR
- Higher concentration of reacting particles causes an increase in the rate of collisions between reacting particles = increased RR
8
Q
RR GAS PRESSURE
A
- Raising pressure by reducing volume or adding gas creates greater concentration of reacting gas molecules
- Increase in rate of collisions = increase RR
9
Q
RR TEMPERATURE
A
- 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
10
Q
RR STATE OF SUB DIVISION
A
- 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
11
Q
RR CATALYSTS
A
- 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
12
Q
INORGANIC CATALYSTS
A
- Platinum
- Manganese Dioxide
- Metal elements or simple ionic compounds
13
Q
BIOLOGICAL CATALYSTS – ENZYEMES
A
- 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
14
Q
CATALYSTS CONTRIBUTING TO SUSTAINABILITY (HABER BOSCH)
A
- 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
15
Q
FRITZ HABER
A
- 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
16
Q
CARL BOSCH
A
- 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
17
Q
MOTOR VEHICLE CATALYTIC CONVERTER
A
- 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
18
Q
HETEROGENEOUS CATALYSTS
A
- 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
19
Q
NANOFORM CATALYSTS
A
- 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
20
Q
HABER BOSCH PROCESS
A
- 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
21
Q
ENZYMES
A
- 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
22
Q
CATALASE
A
- enzyme
- human body
- responsible for rapid catalytic decompostion of H2O2
- one of fastest acting catalysts
