Reaction Ratesss!

Question 1

What is a Reaction Rate?

Answer 1

This is a measure of how fast a certain reaction takes place, measuring how quick a product is formed/used!

Question 2

What are the 3 Ways of finding Rate of Reaction?

Answer 2

• Conc Change/ Time = mol/dm3
• Mass Change/Time = g/s
• Vol Change/Time = cm3/s

Question 3

How does Temprature affect Reaction Rate?

Answer 3

• Temp Increase = Rectant particles gain thermal energy, converted into kinetic energy
• Faster moving particles = increased frequency of particle collision, with more frequent, successfull particle collision, increased RofR!

Question 4

How does Concentration affect reate of reaction?

Answer 4

• Conc Increase = More particles per unit volume, more frequent, successfull collisions!
• Increased number of moles of particles per unit volume!, all being MUCH CLOSER TOGETHER!!

Question 5

How does Pressure affect Raction Rate?

Answer 5

• In gasses, pressure increase = particles subject to a smaller volume, for same number of moles of gaseous particles
• This will mean closer particle proximities, meaning more frequent, successfull collisoins per unit time!

Question 6

How does Surface Srea affect Reaction Rate?

Answer 6

• Increase in SA:V Ratio will mean more particles exposed for particle collisions
• More frequent, successfull collisions per unit time!

Question 7

How does catalysts affect rate of reactions?

Answer 7

• This will provide an alternate reaction pathway!
• This will mean a decrease in activation energy, meaning a greater proportion of particles with SUFFICIENT ENERGY to undergo M.S.F.Colls!

Question 8

What is an Intermediate??

Answer 8

This is a species formed during a reaction that reacts further, that is NOT PRESENT IN THE FINAL PRODUCTS!!!!!

Question 9

What does a catalyst really do?

Answer 9

• NOT used in chemical reaction
• Can react with reactant to form a termporaty intermediate!

“Catalyst will react with reactant to form intermediate, where immediate will break down to give product, while catalyst regenerates“

Question 10

What are Homogenous Catalysts?

Answer 10

1. These are catalysts with SAME PHYSICAL STATE AS REACTANTS!

Question 11

What are examples of Homogenous Catalysts?

Answer 11

1. Ethanol + Ethanoic Acid > Ester + Water [sulfuric acid as catalyst] ((all liquid))
2. Ozone Depletion into Oxygen&raquo_space; [Cloride ion radical as catalyst] ((all gasess))

Question 12

What are Heterogenus Catalysts?

Answer 12

• These are catalysts with DIFFERENT PHYSICAL STATES to the reactants
• Usually** solids with gasous reactants**, in solution
• Reactants molecules are ABSORBED onto catalyst surface, reaction occurs, and products leave via DESORPTION!

Question 13

What are examples of Heterogenous Catalysts at work?

Answer 13

1. Making Ammonia! [iron catalyst]
2. Alkene Hydrogenation (adding H2) [nickel catalyst]

Question 14

How do catalysts help with reactivity benefits?

Answer 14

• Reducing A.E = Less energy required to start reaction
• Less energy = less fossil fuels burned, meaning less non-renewable energy used = less GH released!
• Differing, more feasible reactions able to be used!!

Question 15

What is the Boltzmann Distribution?

Answer 15

1. A graph that shows the proportions of the molecules with a given energy, compared to the energy change of the reaction progression!

Question 15

What are the 3 key features of a Boltzmann Distribution?

Answer 15

1. No molecules will have ZERO ENERGY (hence graph starting at origin)
2. Area under graph = total number of particles
3. No maximum energy for a molecule = curve not meeting x axis at high energy [asymptote]
4. Most have intermediate energy [most probable]…

Question 16

How does a catalyst affect Boltzmann Distribution?

Answer 16

1. Will ** provide alternate reaction pathway and lower activation energy = greater proportion of molecules with sufficent energy to successfully collide and react!**
2. Will move “Ea” line backwards, as a result..

Question 17

How does a temprature affect Boltzmann Distribution?

Answer 17

1. Decrease in peak + Righ-Shift, as total number of particles remain the same!!
2. More molecule with greater/equal energy to A.E.
3. Greater proportion of molecules able to undergo more frequent, successfull collisions
4. Molecules moving faster, due to more particles with increased K.E + T.E!!

Question 18

What is the Rate Equation?

Answer 18

1. Equation linking rate of reaction to concentration of reactants!
2. Experimnets needed to find equation
3. may include substances NOT present in reaction equation!

k = RATE CONSTANT, r = reaction rate, [ ] = conc of..

Question 19

What is Order of Reaction?

Answer 19

1. Tells how much a conc of reactant affects the reaction rate!
2. Individual Order = Power of reactant conc, Overall Order = Σ of individual orders!

Question 20

Finding units for “k” in Rate Equation…

Answer 20

1. Conc = moldm-3, Rate = moldm-3
2. Rearrange to find “k”, after subbing!
3. 0&raquo_space; moldm-3s-1 / 1&raquo_space; s-1 / 2&raquo_space; dm3mol-1s-1 / 3&raquo_space; dm6mol-2s-1

Question 21

Describe and Explain a Rate vs Conc Graph [0,1,2 orders..]

Answer 21

1. 0 = Rate will not depend on this conc AT ALL&raquo_space; Straight Line parralel to X axis!
2. 1 = rate proportional to conc here&raquo_space; fixed straight line at origin, grad = “k”!
3. 2 = Exponential affect on reactant “[ ]”&raquo_space; Upward sloping curve, gives quadratic look

Question 22

Describe and Explain a Conc vs Time Graph [0,1,2 orders..]

Answer 22

1. 0 = constant rate of decreasing conc&raquo_space; straight line downwards, grad = “k”
2. 1 = decreases be a constant half-life&raquo_space; *sloping curve downward, *
3. 2 = Exponential decrease in conc&raquo_space; EVEN MORE sloping of curve than 1

Question 23

Link between conc/time and rate/conc graphs, and why not perfect in reality?

Answer 23

1. DIFFERENTIALS OF ONE ANOTHER (dy/dx)
2. Will be difficult to ISOLATE certain reactants from one another…….

Question 24

How to find "k" from **1st Order conc/time graph!**

Answer 24

1. FIND HALF-LIFE1 2. K = ln(2)/half life to find K , remebereing to include unis (s-1)

Question 25

what is a *clock reaction?*

Answer 25

* time **taken for an observable metric to change** , how rate changes with reactnant conc! * repeated at different reactant concs, *approximation at the initial reaction rate*, depends on **time length for observable change**

Question 26

how accurate are *clock reactions?*

Answer 26

1. WILL BE MORE ACCURATE when LESS time of reaction duration has passed.... 2. *closer to actual* start = *more accuate* inital rate

Question 27

when faced with initial rates table....?

Answer 27

1. ALWAYS find individual orders **>** rate equation **>** find "k" with units **>** sub values for question.....

Question 28

what is the ***Rate Determining Step?***

Answer 28

1. *SLOWEST STEP* in a multi-step reaction (determines overall reaction rate).. 2. each step in reaction requires *individual* rate constants.... 3. SPECIES involved **IN, or BEFORE this step in rate equation ONLY!**

Question 29

How to find mechanisms using **Rate Determining Steps?**

Answer 29

1. Summarise, ensures that RATE EQUATION SPECIES involved in SLOWEST STEP 2. ***ONLY*** If R equation involves species not in product, MUST be CATALYST being REGENERATED!

Question 30

How to replace ***INTERMEDIATES*** in rate equation with real **reactants/products?**

Answer 30

1. USING products/reactants in both steps, use "maths substituting rule" to replace intermediates with real products/reactants 2. obeys the rule, as SPECIES involved **IN, or BEFORE this step in rate equation ONLY!** *[A][A] = [A] SQUARED*