Rates of Reaction Year 11

Question 1

what is meant by a rate of reaction

Answer 1

the speed at which a chemical reaction happens

Question 2

give both formulas for mean rate of reaction with units

Answer 2

amount of reactant used / time taken

amount of product formed/ time taken

rate of reaction is measured in g/s or cm3/s or mol/s

Question 3

what 5 factors affect the rate of a reaction

Answer 3

• increased concentration (of reactants in a solution)
• increased pressure (of reacting gases)
• increased temperature
• increased surface area (of solid reactants)
• the presence/ use of catalysts

Question 4

how does surface area affect the rate of a reaction

Answer 4

• the smaller the pieces, the larger the surface area, the faster the rate of reaction

if the solid is split into several pieces, SA increases

any reaction involving a solid can only happen at the surface of the solid

Question 5

how does concentration affect the rate of a reaction

Answer 5

• the higher the concentration of a dissolved reactant (in liquid), the faster the rate of reaction

Question 6

how does pressure affect the rate of a reaction

Answer 6

• the higher the pressure, the faster the rate of reaction

Question 7

how does temperature affect the rate of a reaction

Answer 7

• the higher the temperature, the faster the rate of reaction

Question 8

what do catalysts do and what happens to them in a reaction?

Answer 8

• speeds up a reaction
• they are not used up in the reaction itself
• they decrease the activation energy needed for the reaction to occur

Question 9

draw diagrams to represent the effect of a low and high concentration on a reaction

Answer 9

LOW………………………………………….HIGH
. O I O O
. O I O O
. O I O O O
. O I O O
. O I O O O O
. O I O O
. O I O O O
more particles = more collisions

Question 10

what type of collision between particles can allow for a chemical reaction to occur?

Answer 10

-reactant particles must collide

Question 11

in terms of particles, how does increasing the temperature affect the rate of reaction?

Answer 11

• at a higher temperature, particles have more energy so move faster and are more likely to collide
• the particles collide with more energy so the number of successful collisions increases

Question 12

how do catalysts affect the rate of reaction?

Answer 12

• they provide alternative reaction pathway creating more collisions, meaning a higher rate of reaction

Question 13

in terms of particles, how does increasing the concentration affect the rate of reaction?

Answer 13

• at a higher concentration, there are more particles in the same amount of space
• this means the particles are more likely to collide therefore more likely to react

Question 14

in terms of particles, how does increasing the surface area affect the rate of reaction?

Answer 14

• if the solid is split into several pieces, the SA increases meaning there is an increased area for the reactant particles to collide with
• the smaller the pieces the larger the surface area meaning more collisions so a greater chance of reaction

Question 15

in terms of particles, how does increasing the pressure affect the rate of reaction?

Answer 15

• as the pressure increases, the space which the gas particles are moving becomes smaller
• the gas particles become closer together, increasing the frequency of collisions meaning particles are more likely to react

Question 16

what is meant by the term activation energy? why do particles need this energy

Answer 16

• the minimum amount of energy that particles must have if they are to react when they collide.
• particles need this much energy to break the bonds in the reactants & start the reaction

Question 17

which reaction would have the fastest rate, A or B and why?
A) 2g solid strip of Mg with water
B) 2g powdered Mg with water

Answer 17

• B

- powder has a higher surface area to volume ratio than the solid strip

Question 18

which reaction would have the fastest rate, A or B and why?
A) 2mol/dm3 HCL with excess ethanoic acid
B) 4mol/dm3 HCL with excess ethanoic acid

Answer 18

• B

- 4mol/dm3 HCL solution is more concentrated than the 2mol/dm3 HCL solution

Question 19

what is collision theory

Answer 19

the idea that the rate of a reaction depends on:

• the frequency of collisions btwn particles. more collisions = faster reaction
• the energy with which particles collide

The collision between the molecules in a chemical reaction provides the kinetic energy needed to break the necessary bonds so that new bonds can be formed.

Question 20

how could you calculate the rate of reaction at a specific time?

Answer 20

• draw a tangent to the curve at the specific time
• construct a right angled triangle using the the tangent as the longest side
• change in y (product)/change in x (time)

Question 21

calculate the rate of reaction btwn CaCO3 and HCL in which 0.6g of CaCO3 was used up after 2.5 mins

Answer 21

0.6/2.5 = 0.24g/min

Question 22

calculate the rate of reaction btwn Li and H2O in which 2.5 x 10^-3 moles of H2 was produced in 10 seconds

Answer 22

(2.5 x 10^-3)/10 = 0.00025 mol/sec

Question 23

calculate the rate of the decomposition of hydrogen peroxide (H2O2) in which 15cm of O2 was produced after 6 mins

Answer 23

15/6 = 2.5cm3/min

Question 24

name the salt produced in the reaction between zinc granules and sulfuric acid

Answer 24

zinc sulfate

Question 25

what are the main methods for meausring the rate of reaction

Answer 25

- measuring the increasing volume of a gas given off - measuring the decreasing mass of a reaction mixture - measuring the decreasing light passing through a solution

Question 26

what would the gradient look like on a graph showing the decreasing mass of a reaction mixture

Answer 26

- steep gradient to start showing a fast reaction | - shallow gradient at the end showing a slow reaction

Question 27

what would the gradient look like on a graph showing the increasing mass of a reaction mixture

Answer 27

- shallow gradient to start showing a slow reaction | - steep gradient at the end showing a fast reaction

Question 28

what happens if particles collide with less energy than the activation energy?

Answer 28

they will not react and will just bounce off each other

Question 29

what would the gradient show on a graph showing the rate of a reaction

Answer 29

steep slope = fast reaction shallow slope = slow reaction no slope = no reaction

Question 30

what happens in terms of particles and reactants as a reaction progresses

Answer 30

- the concentration of reactants decreases | - this reduces the frequency of collisions btwn particles so the reaction slows down & stops

Question 31

how do catalysts decrease the activation energy needed for a reation to occur?

Answer 31

by providing an alternative reaction pathway meaning a lower activation energy is required for the reaction to occur

Question 32

state two properties of the collisions between particles that affect the rate of a reaction

Answer 32

- the frequency of collisions | - the energy with which particles collide

Question 33

use collision theory to explain why increasing the concentration of a reactant increases the rate of reaciton

Answer 33

- there are more particles in a given volume so the collisions btwn particles are more frequent

Question 34

explian why cutting the reactant (magnesium) into smaller pieces increases the rate of reaction

Answer 34

- smaller pieces have a higher surface area to volume ratio | - for the same volume of solid the particles around it have more area to work on so collisions will be more frequent

Question 35

how would you expect a reaction to change if the reactant (magnesium) was cut into smaller pieces

Answer 35

it would increase

Question 36

other than changing the concentration and size of reactant, what other change could be made to change the rate of reaction?

Answer 36

changing the temperature | adding a catalyst

Question 37

explain using collision theory if increasing the volume of a reaction vessel would increase the rate of reaction

Answer 37

- increasing the volume decreases the pressure of the reacting gases - the particles would be more sprea out so would collide less frequently - therefore the reaction rate decreases not increases

Question 38

explain using collision theory if increasing the temperature at which a reaction is carried out would increase the rate of reaction

Answer 38

- increasing the temperature causes the particles the move faster so the frequency of collisions increases - therefore the rate of reaction increases

Question 39

when cerium oxide is mixed with hydrogen and iodine gases the rate of reaction increases. what does this suggest about cerium oxide?

Answer 39

it is a catalyst

Question 40

will the reaction equation change if a catalyst is present in the reaction vessel. why?

Answer 40

- it wont change. | - the catalyst inst used up in the reaction so wont appear in the reaction equation

Question 41

how is the rate of reaction measured?

Answer 41

dividing the amount of reactants used up or products formed by the time taken for the reaction complete

Question 42

which do you take measurements of to work out the rate of reaction: - mass - volume of solution - volume of gas - frequency?

Answer 42

mass | volume of gas

Question 43

a student times how long it takes for a solution to go cloudy at certain temperatures to investigate how the rate of reaction is affected by temperature identify the dependent, independent and one controlled variable in this experiment

Answer 43

``` dependent - time taken for solution to go cloudy independent - temperature controlled - volume of the reactants ```

Question 44

define a dependent variable

Answer 44

- the variable being tested and measured in an experiment. | - As the independent variable is changed the change in the dependent variable is observed and recorded.

Question 45

define a independent variable

Answer 45

- the variable that is changed or controlled in an experiment. - variables that the experimenter changes to test their dependent variable

Question 46

define a controlled variable

Answer 46

- the variable which is constant and unchanged throughout the course of the experiment

Question 47

in an experiment, a gas is produced. - would it be more accurate to measure the rate of reaction by timing how long it take for the solution to go cloudy or how long it takes a volume of gas to be produced? why?

Answer 47

- volume of gas to be produced bc this method is less subjective ie a gas syringe