10- Reaction Rates and Equilibrium

Question 1

What is rate of reaction ?

Answer 1

the change in concentration of a reactant or product in a given time

Question 2

How do you calculate rate?

Answer 2

change in concentration / time

Question 3

What makes an effective collision?

Answer 3

-particles must have sufficient energy to overcome the activation energy barrier of the reaction
-particles must collide in correct orientation

Question 4

What factors can affect the rate of chemical reaction?

Answer 4

-concentration (or pressure when reactants are gases)
-temperature
-use of a catalyst
-surface area of solid reactants

Question 5

What effect does increasing temperature have on reaction rate?

Answer 5

reaction rate increases

Question 6

Explain why increase temperature has its effect on reaction rate?

Answer 6

-particles have more energy
-higher speed
-more frequent collisions
-more successful collisions
-rate increases

Question 7

What is the rule of thumb for reaction rate and temperature?

Answer 7

A 10C increase in temperature doubles the rate of

Question 8

What effect does increasing concentration/pressure have on reaction rate?

Answer 8

reaction rate increases

Question 9

Explain why increasing concentration/pressure has its effect on reaction rate

Answer 9

-concentration increases
-more particles per unit volume
-particles closer together
-more frequent collisions
-more successful collisions
-rate increases

Question 10

How can progress of a chemical reaction be followed?

Answer 10

-monitoring the removal of a reactant
-following the formation of a product

Question 11

What are the two methods of determining reaction rate, when a gas is produced?

Answer 11

-monitoring the volume of gas produced at regular time intervals using gas collection
-monitoring the loss of mass of reactants using a balance

Question 12

When is the rate of reaction the fastest?

Answer 12

-at the start of the reaction, as each reactant is at its highest concentration
-slows down as the reaction proceeds, because the reactants are being used up and their concentrations decrease
-once one of the reactants has been completely used up, the concentration stops changing and the rate of reaction is zero

Question 13

What does collision theory state?

Answer 13

-two reacting particles must collide for a reaction to occur
-only a small proportion of collisions result in a chemical reaction
-in most collisions, molecules collide but then bounce off each other and remain chemically unchanged

Question 14

How do you calculate rate of reaction from graphs?

Answer 14

-draw a tangent
-calculate its gradient (change in y / change in x)

Question 15

What is a catalyst?

Answer 15

a substance that change the rate of a chemical reaction without undergoing any permanent change itself

Question 16

What are the main properties of a catalyst?

Answer 16

-not used up in the reaction
-may react with a reactant to from an intermediate or may provide a surface for the reaction to take place
-the catalyst is regenerated at the end of the reaction

Question 17

How does a catalyst increase the rate of reaction?

Answer 17

-provides an alternate reaction pathway with a lower activation energy. A greater proportion of molecules have more energy greater than or equal to activation energy

Question 18

What is a homogenous catalyst?

Answer 18

Has the same physical state as the reactants

Question 19

How does a homogeneous catalyst interact with the reactants?

Answer 19

-froms an intermediate
-this intermediate then breaks down to give the product and regenerates the catalyst

Question 20

Give 2 examples of homogenous catalysts?

Answer 20

-sulfuric acid (H2SO4) in production of esters
-chlorine radicals in ozone depletion

Question 21

What is a heterogenous catalyst?

Answer 21

has a different physical state from the reactants

Question 22

How does a heterogeneous catalyst interact with reactants?

Answer 22

-Usually solids in contact with gaseous reactants or reactants in solution
-reactants are absorbed onto the surface of catalyst where the reaction takes place
-after the reaction, the products leave the surface of catalyst by desorption

Question 23

Give examples of heterogenous catalysts?

Answer 23

-iron in making ammonia
-platinum or rhodium in reforming
-nickel in hydrogenation of alkenes
-vanadium oxide in making sulfur trioxide

Question 24

What are the benefits of using a catalyst?

Answer 24

-increase rate of reaction by lowering activation energy
-reduced temperature, lower energy demand = lower CO2 emissions
-greater atom economy, reduced use of toxic solvents and reactants
-products made faster and cuts costs and increases profit
-less fossil fuels used = cuts emissions of CO2

Question 25

What is autocatalysis?

Answer 25

A reaction product acts as a catalyst for that reaction

Question 26

What are the main features of Boltzmann distribution?

Answer 26

-no molecules have zero energy (curve starts at the origin)
-the area under the curve is equal to the total number of molecules
-there is no maximum energy for a molecule (the curve does not meet the x axis at high energy. the curve would need to reach infinite energy to meet the x-axis

Question 27

How does the Boltzmann distribution curve change when temperature is increased?

Answer 27

-the peak is lower and shifted to the right (peak at higher energy)
-a greater proportion of molecules can overcome the activation energy
-number of molecules is the same so area under earth the curve remains the same

Question 28

In terms of molecules and collisions what occurs at higher temperatures?

Answer 28

-more molecules have an energy greater than or equal to the activation energy
-therefore a greater proportion of collisions will lead to a reaction, increasing the rate of reaction
-collisions will be more frequent as molecules have greater kinetic energy

Question 29

How does the Boltzmann distribution show the effect of a catalyst?

Answer 29

-activation energy with a catalyst is lower then normal activation energy
-therefore a greater proportion of molecules exceed the new lower activation energy (Ec)
-(on collision) a greater proportion of molecules will react to form products