rates of chemical reactions AOS2

Question 1

what information does a chemical eq give?

Answer 1

the chemical equation for a reaction indicates the nature of the reactants + products but it provides no info about the way in which the reaction proceeds (speed + intensity + how products form)

Question 2

how is the rate of reaction calculated?

Answer 2

found by change in concentration/time (in seconds), the usual unit for rate of reaction is moles per litre per second

Question 3

how to experimental determine the rate of a reaction?

Answer 3

measure how much of a reactant is being used up or how much product is being formed in a given time period this could possibly involve measuring changes in gas volume/mass over time (for gases) + changes in pH or of colour which could be used through colorimetry

Question 4

what does a steeper initial gradient mean on a graph?

Answer 4

it indicates that the initial rate of production of a gas (or other substance) is greater than the rate of reaction later in the experiment. the greater the gradient of the tangent, the faster the reaction rate and the point which acts as the maximum gradient also shows the maximum rate

Question 5

how can changes in gradient be found on graphs?

Answer 5

changes in the rate of reaction can be found by drawing gradients of graphs of the change in mass/volume of a reacting mixture over time

Question 6

what’s the collision theory ->
background info on why collisions occur in reactions?

Answer 6

chemical reactions occur as a result of collisions between the reacting particles, this idea is part of the collision theory of reaction rates. during chemical reactions, particles (atoms, molecules, ions) collide + are rearranged to produce new particles and in a reaction in order to form the products the (covalent?) bonds within molecules must be broken which also requires energy

Question 7

the principles of the collision theory?

Answer 7

according to collision theory for a reaction to occur the reactant + product must collide with each other, collide with sufficient energy to break the bonds within the reactants and collide with the correct orientation to break the bonds within the reactants which allows for the formation of new products. IF A COLLISION DOESN’T MEET ALL OF THE REQUIREMENTS, THEN NO REACTION OCCURS

Question 8

why does a reaction require activation energy?

Answer 8

for a reaction to occur between reactant molecules, the molecules must collide with a certain minimum amount of energy, unless the min amount of energy is met/exceeded the colliding molecules will rebound and simply move away from each other without reacting

Question 9

what is activation energy?

Answer 9

it is the minimum energy that collision must possess for a reaction to occur, when the energy of a collision is greater than/equal to the activation energy can occur. activation energy (Ea) can be represented on an energy profile diagram

Question 10

what’s an energy profile diagram?

Answer 10

activation energy can be represented on an energy profile diagram which represents the potential energies of the reactants + the products over the course of the reaction. the energy change during a reaction is represented on an energy profile diagram as delta H which is the difference in energy between the reactants + the products. the peak on an energy profile diagram represents the activation energy which is the min energy that must be absorbs to break the bonds of reactions so that a chemical reaction can progress. the activation energy is measured form the energy of the reactants to the top of the peak.

Question 11

what’s an exothermic reaction?

Answer 11

this reaction releases more heat energy during the reaction than it absorbs so they consequently result in an increase in the temp of the surroundings (up then down)

Question 12

what’s an endothermic reaction?

Answer 12

it absorbs more heat energy during the reaction that it releases so the temp of the surroundings decreases (down then up)

Question 13

what’s the transition state?

Answer 13

this occurs once the activation energy is absorbs which prompts a new arrangement of the atoms to occur which occurs at the stage of max potential energy in the reaction: the activation energy. bond-breaking + bond-forming are both occurring at the stage and the arrangement of atoms is unstable hence the atoms in the transition state rearrange into the products as the reaction progresses

Question 14

what does the magnitude of the activation energy determine?

Answer 14

it determines how easy it is or a reaction to occur and therefore what proportion of collisions result in a successful reaction. for this reason the reaction rate is dependent upon the activation energy, the resistance of an activation energy for a reaction means that collisions between reactants don’t always result in a chemical change

Question 15

why is the orientation of colliding molecules important?

Answer 15

for a reaction to occur, reactants need to collide with enough energy to provide the activation energy. reacting molecules must also collide with each other in the correct orientation in such a way that particular bonds in the reactants are broken + new bonds are formed in the products. if the collision orientation is incorrect, the particles simply bounce off each other so no reaction occurs. so if there is favourable orientant then a reaction is likely

Question 16

what change can alter the rate of a reaction?

Answer 16

a change in surface area of a solid reactant, concentration of reactants in a solution, pressure of any gaseous reactants, temperature of the reaction, presence of a catalyst

Question 17

how much energy does colliding particles have in any given reaction mixture?

Answer 17

in any given reaction mixture, only a certain proportion of collision between reactant particles have energy that is greater than or equal to the activation energy and the correct orientation for reaction (like ones that are successful)

Question 18

what to increase in order to increase the rate of the reaction?

Answer 18

the frequency of successful collisions by increasing the number of collisions that can occur in a given time and the proportion of collisions that have energy that is greater than or equal to the activation energy by increasing the energy of all collisions

Question 19

what does a successful collision look like?

Answer 19

in a successful collision, the energy must be equal to or greater than the activation energy and the reactants must collide with the correct orientation to break their bonds, allowing the formation of new products

Question 20

how to increase the frequency of collisions?

Answer 20

the rate of reaction increases as the frequency of collisions increases. furthermore, this can occur through increasing the concentration or pressure of the reactants (since collisions occur more frequently when particles are closer together) and through increasing the surface area of a solid reactant

Question 21

what is the link between rate of reaction and increasing concentration?

Answer 21

the rate of a reaction increases when the frequency of collisions between reactants increases. when the concentration of a solution increases, there are more reactant particles moving randomly in a given volume of solution hence the frequency of collisions + successful collisions increases

Question 22

what is the link between rate of reaction and increasing pressure?

Answer 22

for a reaction in the gas phase, the pressure of the gases can be increased either by adding more of the reacting gas to a fixed-volume container or by decreasing the volume of a container with a variable volume, like a gas syringe. increasing the pressure increases the concentration of gas molecules, causing more frequent collisions and increasing the number of successful collisions (frequency of collisions with energy equal/greater than the activation energy) in a given time

Question 23

impact of increasing surface area to the rate of a reaction?

Answer 23

a greater number of exposed solid reactant particles results in a greater frequency of collisions between reactant particles therefore the rate of the reaction increases as well

Question 24

what is the surface area of solids?

Answer 24

when a solid is involved in a reaction, only the particles at the surface of the solid participate in the reaction. the number of particles at the surface depend on the SA of the substance

Question 25

what must you do when referencing the collision theory to explain the effect of concentration, pressure + SA on the rate of a chemical reaction

Answer 25

must discuss the effect on either collision frequency or the number of successful collision per unit time

Question 26

what is the link between kinetic energy + temperature + number of successful collisions in a reaction?

Answer 26

as the temp of a reaction system increases, the average kinetic energy of the particles increases and therefore the average speed of the particles in the system increases. with increased kinetic energy, the frequency of collisions increases (+freq of successful collisions with correct orientation and higher/same energy as the activation energy)

Question 27

what is the impact of temperature on rate of reaction?

Answer 27

collisions occurring at higher temperatures have a greater energy than those at lower temperatures due to the increased kinetic energy of the particles. a greater portion of particles will have the energies that are greater than or equal to activation energy so the proportion of successful collisions increases. the main reason why the reaction rate increases is that a greater proportion of particles have sufficient energy to overcome the activation energy barrier of the reaction which can be understood by considering the range of kinetic energies that occur at each temperature

Question 28

what is the Maxwell-Boltzmann distribution?

Answer 28

at any particular temp, the particles in a substance have a range of kinetic energies although most of the particles have similar kinetic energies there are always some particles with a high or low energy. this range of energies is shown on a graph called the Maxwell-Boltzmann distribution curve

Question 29

how does the Maxwell-Boltzmann distribution curve work?

Answer 29

during a reaction at a given temp, only a small proportion of the reactant particles have kinetic energy that is greater than or equal to the activation energy and so can react. the area under the curve which is equal to the Toal number of particles in the sample, stays constant when the temp is changed. this curve ultimately shows that as the temperature increases, a greater proportion of the molecules have an energy that is greater than or equal to the activation energy which explains the increase in rate as temperature increases

Question 30

what is the activation energy?

Answer 30

the minimum amount of energy required for a reaction to take place and on an energy profile is measured from the energy of the reactants to the peak of the energy profil diagram

Question 31

how is enthalpy found in energy profile diagrams?

Answer 31

is equal to the difference in energy between the products and the reactants

Question 32

what are the properties of catalysts?

Answer 32

they are not consumed during the reactions they seed up and therefore they do not appear as either reactants or products in reaction equations. catalysts are able to increase the rate of reaction because they provide an alternative pathway which decreases the (required) activation energy of the overall reaction dramatically. with a catalyst + lower activation energy, the colliding particles are more likely to have energies that exceed the activation energy, causing the bonds in the reactants to be broken more frequently and as a result a greater proportion of collisions are successful (lead to the formation of products) hence the rate of reaction is increased. however the enthalpies of the reactants and the products are the same so there is no change to the change in enthalpy for the reaction.

Question 33

what does the peak of an energy profile diagram represent?

Answer 33

the transition state

Question 34

what are the 2 types of catalysts?

Answer 34

Homogeneous and heterogeneous catalysts which are used depending on the physical state of the chemicals involved in the reaction

Question 35

what are homogeneous catalysts?

Answer 35

catalysts that are in the same physical state as the reactants and the products of the reaction

Question 36

what are heterogenous catalysts?

Answer 36

catalysts that are in a different physical state to the reactants and products of the reaction

Question 37

why do chemists prefer to work with heterogeneous catalysts?

Answer 37

they are more easily separated from the products of a reaction, much easier to use and are able to be used at high temperatures.

Question 38

what is absorption - for the use of catalysts in industries?

Answer 38

particles at the surface of some solids of high surface area tend to absorb (form a bond with) gas molecules that strike the surface. absorption distorts bonds in the gas molecules or may even completely break them down, allowing a reaction to proceed more easily that it would if the solid were absent. these solid surfaces provide a new way for the reaction to occur (new pathway) that has a significantly lower activation energy

Question 39

why are solid catalysts used in a powdered or sponge-like form in industries?

Answer 39

this is done to provide the greatest possible surface area because with a larger surface area, more reactant molecules can be absorbed and the reaction is even faster