unit 3 aos 2 - rate of reactions

Question 1

rate of reaction

Answer 1

how quickly something is reacting

Question 2

What are the requirements that need to be fulfilled for two reactants to react with eachother

Answer 2

• have sufficent energy
• must collide (make contact)
• and collide with the correct orientation

Question 3

how to INCREASE the frequency of collisions?

Answer 3

• add more reactants
• decrease the volume (space)
• increase the average kinetic energy (increase the temp)

Question 4

concentration and pressure

Answer 4

DEF: how tightly packed a mixture is.

CONCENTRATION: used for aqueous mixtures

PRESSURE: used for gasseous mixtures

Question 5

relationship BTWN pressure and volume

Answer 5

as VOLUME decreases, PRESSURE increases

Question 6

relationship BTWN concentration and volume

Answer 6

as volume increases (more in sol), CONCENTRATION decreases

Question 7

SAMPLE RESONSE:
If there is an INCREASE (decrease) in concentration or pressure

Answer 7

1) when concentration/pressure is increased(decreased), particles move closer togeather (futher apart)
2) frequency of total collisions increase (decrease)
3) frequence of friutful collisiosn with correct orientation increases (decreases)
4) overall rate of reaction increases (decreases)

Question 8

does increasing the concentration/oressure change the proportion or probability of fruitful/sucessful collisions?

Answer 8

NO. there is no change.

• in these responses DO NOT MENTION probabiltiy/protortion of sucessful collisions

Question 9

effect of adding an INERT gas on the rate of reaction

Answer 9

• when an inert gas is added, the overall pressure INCREASES.
• partial pressure of reactants: stay the same
• Frequency of collisions between reactants: stays the same
• THus Rate of reaction: stays the same

Question 10

sample response for SURFACE AREA.

Answer 10

1) cutting/dividing substances into thin powder INCREASES(decreases) surface area.
2) contact between reactants INCREASE (decrease)
3) total frequency of collisions INCREASES (decreases)
4) thus frequency of fruitful collisions with correct orientation INCREASES (decreases)
4) SO overal rate of reaction INCREASES (decreases)

Question 11

ACTIVATION energy

Answer 11

• DEF: energy required to be inputted to break the pre-exisitiong bonds before a reaction can proceed
• For sucessful reaction: energy greater than the activation energy must be inputted

Question 12

How can we lower the activation energy?

Answer 12

• increase kinetic energy
• decrease the activation energy

Question 13

is temperatrure a type of kinetic energy?

Answer 13

YES bc at higher temperatures, particles move faster.
THUS at greater temps, there are more frequent collisions

Question 14

sample response of EFFECT OF TEMPERATURE.

Answer 14

1) increasing () temp increases () averaage kinetic energy.
2) reacting particles collide with greater () force
3) probability of colliding with sufficient energy to overcome the activation energy increases ()
4) proportion of sucessful collisions also increase ().

5) acerage moving speed of particles increase ()
6) total frequency of collisions increase()
7) frequency of sucessful collisions increase ()

8) THUS overall rate of reaction increases ()

Question 15

catalyst

Answer 15

provides an alternative pathway with lower activation energy by forming temporary and partial intermolecular bonds with the reacting particles

Question 16

catalyst extra info

Answer 16

DECREASES activation energy
INCREASES rate of reaction

also does not change before and after a reaction

Question 17

what happend to the enthalaphy (delta H) with a catlyst

Answer 17

NOTHING. there is no change

Question 18

sample response: EFFECT OF THE ADDITION OF A CATALYST.

Answer 18

1) its addition LOWERE the activation energy by providing an alternative reaction pathway
2) the proportion of particles with sufficent energy to overcome this new activation energy is increased
3) the proportion of fruitful /sucessful collisions is increased. THUS rate of reaction increases

Question 19

how do we measure rates of reaction?

Answer 19

generally through monitering changes we can see:
- mass
-volume
- pH
- temperature
- colour

Question 20

measuring RoR: volume of gas evolved

Answer 20

1) attach a gas syringe to capture the gaseous products

Question 21

measureing RoR: change in mass

Answer 21

only if reaction produces a gas
bc then mass would dreacse over time as gas escapes

Question 22

measuring RoR: change in temp

Answer 22

bc almost every reaction is eaither exothermic or endothermic

Question 23

measuring RoR: pH change

Answer 23

is H= or OH- are used or formed

Question 24

what is a reat vs time graph

Answer 24

the DERIVATIVE (gradient) of volume vs timer graph

Question 25

rate induence on graphs

Answer 25

if rate INCREASED, steaper gradient in graph if rate DEACRESED: more straight gradient, lesser steapness not if only rate changes , PLANTEAU at same spot

Question 26

yeild impact

Answer 26

yeind INCREASE: plateau higher yeild DECREASEL plateau lower

Question 27

what is a reversable reaction?

Answer 27

- a reaction that can go both ways - it can do this eaither simultatiously (at the same time) or sopntaneously (by itself) - in VCAA we olny discuss them in closed systems

Question 28

open system:

Answer 28

matter can be added/removed from the system.

Question 29

closed system:

Answer 29

matter cannot be be added/removed from the system

Question 30

Reasoning why substances stay roughly constant:

Answer 30

Rate of forwards reaction = Rate of backwards reaction aka reaches equilibrium

Question 31

concentration FORMULA

Answer 31

c = n/v [ ]

Question 32

Equilibrium Constant (𝑲)

Answer 32

show the relative concentration of each particle at equilibrium

Question 33

how to find the Equilibrium Constant (𝑲𝒄)

Answer 33

[products] / [reductants] products = right hand sind reactants = left hand side - multiply products - coefficients turn into exponents

Question 34

concentration units

Answer 34

also do Kc equation to find the units - if M cancels out say "no units"

Question 35

Homogenous Equilibrium

Answer 35

Only one state of matter present in equation

Question 36

Heterogenous Equilibrium

Answer 36

Multiple states of matter present in equation

Question 37

Aqueous (𝐚𝐪) or Gaseous (𝐠) Substances

Answer 37

HAVE concentration

Question 38

Solid (𝐬) or Liquid (𝐥) Substances

Answer 38

DO NOT HAVE concentration - so concentration is 1

Question 39

what changfes the equilibrium constant (Kc)?

Answer 39

The equilibrium constant remains constant at the same temperatures - Changes in volume or other species do not change the equilibrium constant!

Question 40

how does the Kc value change if we reverse the equation?

Answer 40

reciprocal it.

Question 41

how does the Kc value change if we multiply/divide coefficients

Answer 41

take Kc value to the power of that multiplied/divided value

Question 42

Small Extent of Reaction

Answer 42

Kc < 10^-4 reactants are favoured

Question 43

Medium Extent of reaction

Answer 43

10^-4 < Kc < 10^4 both are favoured

Question 44

Large extent of reaction

Answer 44

Kc > 10 ^4 products are favoured

Question 45

what is a Reaction Quotient (Qc)?

Answer 45

expressed the same as the equilibrium constant - it can be used to determine which way the reaction goes! - it shows the current value??

Question 46

if Kc = Qc

Answer 46

reaction is at equilibrium

Question 47

if Kc not = to Qc

Answer 47

reaction is not at equilibrium

Question 48

if Qc < Kc

Answer 48

undershot THUS forwards reaction is favoured

Question 49

if Qc = Kc

Answer 49

perfect shot THUS neither reaction is favoured

Question 50

if Qc > Kc

Answer 50

overshoot THUS reverse reaction is favoured

Question 51

RICE table. acronym meaning

Answer 51

R: reaction nI: initial value nC: change nE: equilibrium

Question 52

steps to fill out RICE table

Answer 52

1. Fill out knowns. 2. Find 𝑛C (use stoichiometric ratios & +/− signs.). 3. Find 𝑛E

Question 53

when can we use RICE

Answer 53

“Empty” or “evacuated” means there are no other substances present at the beginning ALSO look at marks 4+ = use RICE

Question 54

Le Châtelier’s Principle

Answer 54

"𝑰𝒇 𝒂 𝒔𝒚𝒔𝒕𝒆𝒎 𝒊𝒔 𝒂𝒕 𝒆𝒒𝒖𝒊𝒍𝒊𝒃𝒓𝒊𝒖𝒎, 𝒂𝒏𝒅 𝒊𝒔 𝒔𝒖𝒃𝒋𝒆𝒄𝒕𝒆𝒅 𝒕𝒐 𝒂 𝒄𝒉𝒂𝒏𝒈𝒆, 𝒕𝒉𝒆 𝒆𝒒𝒖𝒊𝒍𝒊𝒃𝒓𝒊𝒖𝒎 𝒘𝒊𝒍𝒍 𝒔𝒉𝒊𝒇𝒕 𝒕𝒐 𝒑𝒂𝒓𝒕𝒊𝒂𝒍𝒍𝒚 𝒐𝒑𝒑𝒐𝒔𝒆 𝒕𝒉𝒆 𝒄𝒉𝒂𝒏𝒈𝒆. "

Question 55

Sample Response: Le Châtelier’s Principle

Answer 55

There are three things to mention: 1. Mention the initial change which has been made to the system. 2. State Le Châtelier’s Principle explicitly and identify how it will partially oppose the change. 3. State whether the forward/reverse reaction is favoured

Question 56

Removing Substances

Answer 56

Effect: Removing substances causes system to replenish the substances lost. Figure out Shift: Still use water analogy. Explanation Strategy: Apply Le Châtelier’s Principle similarly

Question 57

two ways to remove products

Answer 57

- Neutralisation reaction (Acid/Base). - Precipitation reaction

Question 58

Graphing Equilibrium Changes for Adding Substances

Answer 58

- when something is added, that substance will vertically spike up - changein equilibrium: dependent on stoichometric ratios. grrid is usually provided, so must be done to scale

Question 59

Sample Response: Effect of Volume Change on Equilibrium System

Answer 59

1. Link volume to the overall concentration. 2. Le Châtelier’s Principle states that the system will partially oppose the change in overall concentration by favouring the side with more/less particles! 3. State whether a forwards/reverse reaction is favoured

Question 60

Graphing Volume Change

Answer 60

???

Question 61

Colour Changes in Equilibrium Mixtures

Answer 61

- change in intensity of colour is caused by change in concentration of species. - Le chateliers principle only partially oppose the change so IF an overal concentration of a substance increases then the overall colour change is more intense

Question 62

Volume Change – Same Amount of Reactants and Products

Answer 62

- change in volume/pressure will not change the position of equilibrium as both sides have same amount of products and reactants - if the system,