Rates Of Reaction

Question 1

define the rate of a chemical reaction

Answer 1

the change in concentration of a reactant or a product per unit time

Question 2

what does the collision theory state?

Answer 2

-molecules must collide with each other
-molecules must have energy greater than or equal to the activation energy
-molecules must collide in the correct orientation

Question 3

what is unsuccessful collision?

Answer 3

when molecules collide in incorrect orientation and bounce off one another

Question 4

using the collision theory, explain the effect of concentration on rate

Answer 4

-as the concentration of reactant molecules increases, the reaction increases
-at a higher concentration there are more molecules in a given volume
-so more frequent successful collisions

Question 5

using the collision theory, explain the effect of pressure on rate

Answer 5

-when the pressure of a gas is increased, the gas molecules are pushed closer together
-the number of gas molecules in a given volume increases
-more frequent successful collisions

Question 6

using the collision theory, explain the effect of temperature on rate

Answer 6

-as the temperature of a reaction mixture increases, the rate of reaction increases
-at a higher temperature, the average energy of the molecule increases
-a greater proportion of molecules have energy greater than or equal to the activation energy
-more frequent successful collisions occur

Question 7

define activation energy

Answer 7

the minimum energy required for a reaction to take place by breaking the bonds in the reaction

Question 8

what is a catalysts role in a reaction?

Answer 8

-increases the rate of reaction
-without being used up by the overall reaction
-allows the reaction to proceed via a different route with lower activation energy

Question 9

define a heterogeneous catalysis

Answer 9

-catalysis of a reaction in which the catalyst has a different physical state from the reactants (reactants=(g), catlyst=(s))

Question 10

define homogeneous catalysis

Answer 10

-catalysis of a reaction in which the catalyst and the reactants are in the same physical state (normally aq or g)

Question 11

give 4 examples of advantages using a catalyst in an industrial reaction

Answer 11

-reduced energy demand
-less CO2 emissions as less combustion of fossil fuels is needed
-so less cost and increased sustainability

-alternative reaction with higher atom economy and less waste can be used

Question 12

what are advantages of using enzymes

Answer 12

-generate very specific products
-no side reactions so no by-products made so higher atom economy
-operate close to room temp and pressure milder conditions

Question 13

what heterogenous catlyst is used in the haber process?

Answer 13

iron (S)

Question 14

what heterogenous catalyst is used in making poly(ethene)

Answer 14

ziegler-natta

Question 15

what heterogenous catalyst is use in a catalytic converter to remove toxic gases from car exhausts

Answer 15

alloy of
Rh/Pd/Pt

Question 16

what does a boltzmann distribution show?

Answer 16

the distribution of energies of molecules at a particular temp

Question 17

why does the boltzmann curve start at (0,0)

Answer 17

no molecules have 0 energy

Question 18

what does the shaded area under the boltzmann curve represent?

Answer 18

-the proportion of molecules that have energy greater than or equal to the activation energy
-these molecules have enough energy to react, if they collide in the correct orientation

Question 19

what does the unsymmetrical boltzmann curve shape mean?

Answer 19

more molecules have lower energies

Question 20

explain the effect of temperature on rate of reaction using a boltzmann curve (see pg7)

Answer 20

-at a higher temp, the average energy of the molecules increases
-a greater proportion of the molecules have energy greater than or equal to the activation energy, as shown by the shaded area under the curve at higher temp
-more frequent successful collisions occur
-rate of reaction increases

Question 21

explain the effect of a catalyst using a boltzmann curve (see pg 8)

Answer 21

-a catalyst increases the rate of reaction without being consumed by the overall reaction
-a catalyst lowers the activation energy for the reaction by providing an alternative pathway

-a greater proportion of the molecules have energy greater than or equal to the activation energy as shown by the increase shaded area under the curve when the activation energy is lowered
-more frequent successful collisions occur
-rate of reaction increases in the presence of a catalyst

Question 22

how is the change in concentration of a reactant or product measured

Answer 22

by continuous monitoring at regular time intervals

Question 23

what does a colorimeter determine?

Answer 23

concentration based on absorbance of light

Question 24

how can pH be measured?

Answer 24

pH meter at regular time intervals
sample could be extracted and analysed by titration at regular time intervals

Question 25

what does a concentration-time graph show?

Answer 25

the change in concentration of a reactant or product with time during a chemical reaction

Question 26

what does the initial rate of reaction equal?

Answer 26

the gradient of the tangent at time = 0

Question 27

what is the general rate equation?

Answer 27

K[A]^m[B]^n

Question 28

what does the rate equation show?

Answer 28

the relationship between the rate of reaction and the concentration of the reactants raised to the powers of their orders

Question 29

what condition is K linked with, whats the effect of a larger K value

Answer 29

a larger K value= faster reaction
linked with temperature