12CHB - Term 2

Question 1

Things that affect RoR

Answer 1

Concentration, Surface Area, Temperature, Catalyst, pressure

Question 2

How does concentration affect RoR

Answer 2

Increasing concentration increases the amount of particles in a given volume. Particles are more likely to collide increasing the frequency of collisions and therefore the frequency of successful collisions

Question 3

How does Surface Area affect RoR

Answer 3

There are more exposed particles which are able to react and collide. This increases the frequency of collisions and therefore the frequency of successful collisions

Question 4

How does temperature affect RoR

Answer 4

This does 2 things:
- The particles gain kinetic energy and move faster, this increases the frequency of collisions and therefore successful collisions
- The particles gain energy meaning a larger proportion of them with have energy to overcome the activation energy barrier

Question 5

How does a catalyst affect RoR

Answer 5

Provides an alternate reaction pathway with a lower Ea barrier, without being used up. Therefore a higher proportion of particles can overcome the barrier

Question 6

Define rate of reaction

Answer 6

The decrease in concentration of reactants over time or the increase in concentration of products over time (mol dm-3 s-1)

Question 7

Ways to measure rate of reaction (7)

Answer 7

• Change in colour (Reaction must change colour)
• Change in mass (produces gas)
• Change in volume (produces gas)
• Change in pH (Acid-Base reaction)
• Change in temp (Releases/Absorbs heat)
• Change in conductivity (difference in ions between reactants and products )
• Precipitation forming/Opacity change (Must release precipitate)

Question 8

Color change Br2 => Br -

Answer 8

Brown/Orange -> Colourless

Question 9

Color change MnO4 - => Mn 2+

Answer 9

Purple -> Colourless

Question 10

Color change Cr2O7 2- => Cr 3+

Answer 10

Orange -> Green

Question 11

Define Activation Energy

Answer 11

The minimum value of Ek that particles must have before they are able to react. The difference between reactants and the top of the peak

Question 12

Rate determining step

Answer 12

The slowest step in a reaction mechanism. Determines the rate of reaction

Question 13

Define Order of reaction

Answer 13

The number of moles in the rate determining step. Can be described as overall or with respect to a particular reactant

Question 14

Units of Zero order reaction

Answer 14

mol dm-3 s-1

Question 15

Units of First order reaction

Answer 15

s-1

Question 16

Units of Second order reaction

Answer 16

dm3 mol-1 s-1

Question 17

Units of Third order reaction

Answer 17

dm6 mol-2 s-1

Question 18

Zero Order: concentration-time graph and rate-concentration graph

Answer 18

Concentration-time graph - Straight linear decreasing graph
Rate-concentration graph - Straight line graph flat

Question 18

Rate order equation for a First order reaction

Answer 18

rate = k[A]

Question 19

Rate order equation for a Second order reaction

Answer 19

rate = k[A]^2 or rate = k[A][B]

Question 20

Rate order equation for a Third order reaction

Answer 20

rate = k[A]^2[B] or rate = k[B]^2[A]

Question 21

First Order: concentration-time graph and rate-concentration graph

Answer 21

Concentration-time graph - Exponentially decreasing
Rate-concentration graph - Straight linear increasing graph

Question 22

Second Order: concentration-time graph and rate-concentration graph

Answer 22

Concentration-time graph - Exponentially decreasing very steep
Rate-concentration graph - Exponentially increasing

Question 23

Arrhenius equation

Answer 23

K = Ae^(-Ea/RT)
K = Rate constant (unit is the reaction order unit)
A = Arrhenius constant (same as rate constant units)
Ea = Activation energy (Jmol-1)
R = Universal gas constant (JK-1mol-1)
T = temperature (K)

Question 24

Define Arrhenius energy

Answer 24

It is special to each chemical reaction but is constant for that particular reaction. Quantifies the frequency of collisions with correct orientation

Question 25

What does a graph of ln(k) vs 1/T give

Answer 25

1/T on x-axis and ln(k) on y-axis Gradient = -Ea/R y-intercept = ln(A)

Question 26

How a catalyst and temperature affect a Maxwell Botltzman curve

Answer 26

Catalyst moves the Ea energy to the left Temperature causes the curve to peak later and lower that the original

Question 27

How a catalyst and temperature affect an energy profile diagram

Answer 27

Catalyst causes Ea to decrease Temperature causes the initial Ep to increase, Ea stays the same, reaction ends with more Ep too

Question 28

Define Stoichiometry

Answer 28

Ratio of number of moles

Question 29

Collision theory

Answer 29

1. Particles need to collide 2. Particles need to collide at the correct orientation 3. Particles collide with enough energy (greater than Ea)

Question 30

How does a Pressure affect RoR

Answer 30

An increase in pressure, is more particles in a given volume and will result in more frequent collisions. Therefore, successful collisions also increases

Question 31

Problem with measuring RoR

Answer 31

Reactions that are very fast, timing is more difficult to be accurate, and will have a higher percentage of percentage error