Reaction rates and equilibrium

Question 1

Define ‘the rate of a chemical reaction’

Answer 1

change in concentration of product over time

Question 2

give the formula for finding the rate of a reaction

Answer 2

rate = change in conc/time

Question 3

why is the rate of reaction fastest at the beginning?

Answer 3

each reactant is at its highest conc.

Question 4

what happens to the ROR once one of the reactants has been completely used up?

Answer 4

the conc. stops changing and the rate of reaction is 0

Question 5

what are the 4 factors that can change the rate of a chemical recation

Answer 5

conc.
temp.
use of catalyst.
surface area of solid reactants

Question 6

what makes an effective collision between particles?

Answer 6

• the particles collide with correct orientation

- the particles have sufficient energy to overcome the Ae barier of the reaction

Question 7

how does increasing the pressure of a gas affect the rate of reaction ?

Answer 7

same number of molecules occupy a smaller volume. gas molecules- closer togetehr- collide more freq. leading to more effective collisions in the same time

Question 8

what are the two methods that can be used to determine the ROR for a reaction that produces gases ?

Answer 8

• monitoring the vol. of gas produced at regular time intervals using gas collection
• monitoring the loss of mass of reactants using a balance.

Question 9

what is a catalyst?

Answer 9

provides an alternative rout e for the reaction with a lower Ae.

Question 10

catalyst- not used up
- regenerated at end of R.
what else does it do?

Answer 10

The catalyst may react with a reactant to form an intermediate or may provide a surface on which the R. can take place

Question 11

what are the two types of catalysts?

Answer 11

homogenous and heterogenous

Question 12

what is a homogenous catalyst?

Answer 12

a catalyst that has the same physical state as the reactants.

Question 13

explain what a homogeneous catalyst does.

Answer 13

it reacts with the reactants to form an intermediate. the intermediate then breaks down to give the products and regenerates to give the catalyst.

Question 14

give one example of the use of homogeneous catalysts in chemistry.

Answer 14

making esters using a (homo.) sulfuric acid catalyst,

note: all the reactants and the catalysts are liquids

Question 15

what is the initial rate?

Answer 15

the maximum rate of the reaction , its measured at , and gives the steepest gradient in a concentration time graph , usually at the beginning of the reaction

Question 16

what is a heterogeneous catalyst?

Answer 16

catalysts that are in a different phase to the reactants.

Question 17

what is the Boltzmann distribution ?

Answer 17

shows the distribution of molecular energies in a gas at constant temperature.

Question 18

how does a heterogeneous catalyst work?

Answer 18

provides a surface for reactant molecules for adsorption on which the reaction can take place , after the reaction the product molecules leave the surface of the catalyst .
their work is more effective when the surface area is maximised

Question 19

give one example of a heterogeneous catalyst and its use in industry?

Answer 19

catalytic converters pass gaseous reactants over a solid.

Question 20

explain the haber process

Answer 20

where ammonia is formed in the reaction between nitrogen and hydrogen. The triple bond in nitrogen molecules requires a vast amount of energy to break so Fe is used as a heterogeneous catalyst to weaken this strong bond and to lower the activation energy.

Question 21

uses for ammonia?

Answer 21

fertiliser, refrigerant gas

Question 22

effect of increasing concentration of an aqueous reactant ?

Answer 22

increases number of reactant molecules in a given volume= frequent collisions= increasing the rate of the reaction

Question 23

give two common investigations that can be used to monitor rate of reactions?

Answer 23

• Recording the volume of gas produced using a gas syringe

- using a balance to record loss of mass

Question 24

give some examples of some uncommon investigations that can be used to monitor rate of reactions

Answer 24

• Using a colorimeter to record the change in concentration of coloured substances
• Timing how long it takes for a change to occur, e.g. recording how long it takes for a precipitate to form
• Determining the concentration of a reactant or product by titrating a sample of the reaction mixture

Question 25

what is le chateliers principle ?

Answer 25

When a system in dynamic equilibrium is subjected to a change, the position of the equilibrium will shift to oppose the change.

Question 26

whats the haber process?

Answer 26

formation of NH3 (g) by reacting Nitrogen and hydrogen with an Fe catalyst .