Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Chemistry module 3 > Chapter 10 - reaction rates > Flashcards

Chapter 10 - reaction rates Flashcards

You may prefer our related Brainscape-certified flashcards:
Periodic Table flashcards Chemistry 101 flashcards AP® Chemistry flashcards Organic Chemistry 101 flashcards
1
Q

what is the rate of a chemical reaction in real terms

A

how fast a product is being made or how fast a reactant is being used up

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what is the generalized equation for ROR

A

rate = change in concentration/time

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

what determines the rate of a reaction

A

the frequency of successful collisions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

what determines if something is a successful collision

A
  • correct energy, Ea or higher

- correct orientation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

name the main 4 factors on ROR

A

concentration, temperature, surface area, catalysts

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

define activation energy

A

the minimum energy required for a reaction to take place

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

what are the two ways of measured ROR

A
  • measuring formation of a product

- measuring removal of a reactant

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

how can ROR be measured for a gas release

A
  • use a gas syringe, take the volume of gas at regular intervals
  • use an upturned measuring cylinder and take vols at regular intervals
  • plot graph and take grad
  • OR measure loss of mass over time
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

how can ROR be measured for a precipitate

A

measure how long it takes for a cross underneath a container to no longer be visible where ROR is INVERSELY proportional to time

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

define what a catalyst is

A

“a catalyst is a substance that changes the rate of a chemical reaction without undergoing any permanent changes itself by providing an alternative reaction pathway with a lower activation energy”

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

how do catalysts increase ROR

A

they reduce Ea by providing an alternative reaction pathway

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what is a homogenous catalyst and name an example of a reaction with one

A

a catalyst which is in the same physical state as the reactants, it reacts with the reactants to form an intermediate then breaks down again to form the products and reform the catalyst
e.g.
Cl*(g)
2O3(g), 3O2(g)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

what is a heterogenous catalyst and give an example of a reaction with one

A

a catalyst which is in a different physical state to the reactants, it usually works by the reactants weakly bonding to its surface/ adsorbtion where the reaction takes place then they desorb from the surface after the reaction
e.g.
Fe(s)
N2(g) + 3H2(g) 2NH3(g)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

why do reactions with catalysts tend to be more sustainble/ why are they used in industrial processes

A
  • they reduce the energy required
  • they can also reduce costs
  • they make the reaction faster/more product can be made
  • the catalyst isn’t used up
  • reactions can take place at lower temperatures
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

what does the Boltzmann distribution represent

A
  • the spread of molecular energies in gases
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what are the labels of the axes on a Boltzmann distribution

A 
y-axis = number of molecules with given energy
x-axis = energy
17
Q

how does the distribution change with temperature and what effect does this have

A

the peak moves down and to the right, thus given the area under the graph is finite, the shaded area increases, more particles have greater than or equal to the Ea and thus the FOSC increases so ROR increases

18
Q

why does ROR increase with concentration

A
  • there are more particles per given volume
  • thus particles are more likely to collide
  • this means FOSC increases so ROR increases
19
Q

why does ROR increase with temperature

A
  • the particles move faster so they are more likely to collide and more likely to collide with the Ea so FOSC increases
20
Q

why does a catalyst increase ROR

A
  • reduces Ea by providing an alternative reaction pathway

- more particles react >= Ea so FOSC increases

21
Q

why does increases the S.A. of the reactants increase the ROR

A
  • greater area for collisions to occur on/more available molecules
  • increases FOSC
22
Q

how does the Boltzmann distribution change with the addition of a catalyst

A
  • the shaded line is drawn at a lower energy, more molecules have greater than or equal to the Ea
23
Q

what what are some key features of dynamic equilibrium

A
  • the rates of the forwards and backwards reactions are equal
  • the concentrations of the reactants and products do not change
  • there must be a closed system
24
Q

state le chatalier’s principle

A

“when a system in dynamic equilibrium is subjected to an external change the system readjusts and the position of equilibrium changes to minimize the effect of that change”

25
Q

what is the effect of concentration changes on equilibrium

A
  • for A + B –> C + D
  • if the conc’s of A+B are increased then the position of equilibrium will move right in order to form more products to reduce the conc of A+B
  • and vice versa
26
Q

how can concentration changes with le chatalier’s be investigated

A
  • if the reactants and products are different colours e.g.
    2CrO4^2- + 2H+ —> Cr2O7 ^2- + H2O
    yellow orange
  • if the forward reaction is quicker then the solution will appear more orange
  • if the backwards reaction is quicker then the solution will appear more yellow
27
Q

describe how temperature affects the position of equilibrium

A
  • if forwards reaction is exothermic (-deltaH) then a decreased temperature will increase the forward reaction and an increased temperature will decrease the forwards reaction
  • and vice versa
  • a similar thing as before can be done to investigate this
28
Q

how does a change in pressure affect the position of equilibrium

A

whichever side of the reaction has fewer moles of gas will benefit from increased pressure

29
Q

effect of a catalyst on the position of equilibrium

A
  • a catalyst doesn’t affect the position of equilibrium because it increases the rates of the forwards and backwards reactions BY THE SAME AMOUNT
  • it will mean that equilibrium is reached quicker
30
Q

what does the equilibrium constant mean and what is its formula

A

it provides the actual position of equilibrium
for reaction aA + bB —> cC + dD

Kc = [C]^c [D]^d / [A]^a [B]^b

31
Q

what does <1, =1 and >1 mean in relation to Kc

A

if Kc < 1 then the backwards reaction is favored
if Kc = 1 then equilibrium is halfway
if Kc > 1 then the forwards reaction is favored

32
Q

why does changing concentrations or pressured not affect Kc

A

the system equals out to give the same ratio of concentrations and pressures

33
Q

what does affect Kc

A

changing temperature- it benefits one of the reactions, this permanently changes the position of equilibrium

34
Q

what are the key features of a Boltzmann distribution

A
  • there are no particles with no energy (line passes through origin)
  • the line doesn’t retouch the x-axis but gets close (there aren’t many particles with lots of energy)
  • most particles have average amounts of energy
  • area under the graph = number of particles
  • higher temperature shifts distribution right and down
35
Q

things to remember on catalyst questions

A
  • when asked what the purpose of a catalyst is or effect of a catalyst always mention BY PROVIDING AN ALTERNATIVE REACTION PATHWAY WITH A LOWER ACTIVATION ENERGY
  • what should you say if asked the effect of a catalyst on dynamic equilibrium – No effect because it increases the rate of both reactions BY THE SAME AMOUNT
36
Q

why does rate of reaction get slower as a reaction progresses and when does the reaction stop

A
  • as the reaction proceeds, the concentrations of the reactant particles decreases (because they are used up in the reaction)
  • hence the frequency of successful collisions decreases
  • the reaction stops when ALL OF ONE REACTANT is used up
37
Q

what is the effect on a concentration of products/vol of gas against time graph if a strong acid is replaced by a weak acid or an acid of lower concentration (but same number of moles)

A

the rate of reaction (gradient) is lower but the final volume is the same

38
Q

what is the effect on a concentration-time graph if less of a reactant is used but the same concentration

A

If the reactant is still in excess then there’s no change
if the reactant is not in excess/ is limiting then the rate of reaction is mostly the same as before but it finishes at a lower value

39
Q

why does adding a catalyst to a forming dynamic equilibrium decrease the time taken for the equilibrium to be established

A
  • it decreases the activation energy so the rates of both reactions increase (by the same amount)

Chemistry module 3 (4 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions