Reaction rates

Question 1

What is collision theory

Answer 1

States that a reaction will not take place between two particles unless they collide in the correct orientation and collide with energy greater than or equal to activation energy

Question 2

What is the activation energy

Answer 2

The minimum energy required for the reaction to occur

Question 3

What is rate of reaction

Answer 3

Change in concentration/time (can be the gradient in a graph)

Question 4

How can frequency of collisions be increased

Answer 4

Increase:
Concentration
Pressure
Surface area
Temperature

Question 5

How does increasing concentration in a solution affect rate of reaction

Answer 5

It increases rate of reaction because this increases the number of reactant particles in a given volume and so increases the frequency of collisions between particles therefore more frequent successful collisions

Question 6

Explain how concentration of reactant decreases over time in a graph

Answer 6

Question 7

How does the gradient in a graph relate to the rate of equation

Answer 7

Gradient = rate

Question 8

Formula for gradient

Answer 8

Change in y/change in x

Question 9

What is the trend between volume and pressure

Answer 9

A larger volume creates a lower pressure and vice versa

Question 9

How does a slower reaction affect a gradient in a graph

Answer 9

A slower reaction causes a less steep gradient

Question 10

How does pressure affect rate or reaction

Answer 10

Increase in pressure means that there are more molecules in a given volume, therefore more frequent successful collisions, increasing the rate of reaction .

Question 11

How else can pressure be increased

Answer 11

By increasing the number of molecules in the same volume reaction vessel

Question 12

How does surface area affect rate of reaction

Answer 12

Increasing surface area increasing rates of reaction because this increases the number of particles available for collisions, and so increases the frequency of successful collisions

Question 13

How does temperature affect the rate of reaction

Answer 13

An increase in temperature always increases the rate of reaction. Particles have more energy at higher temperature. This leads to more particles with energy greater than or equal to activation energy therefore more frequent successful collisions.

Question 14

What are the two ways to measure the rate of chemical reaction

Answer 14

Using a continuous monitoring method
Using an initial rate method

Question 15

Explain the continuous monitoring method

Answer 15

Measure either the amount of product formed or the reactant lost continuously throughout the course of one reaction
Then measure (a) conc. of a species reacted or formed (b) volume of gas formed (c) mass lost during a reaction (and therefore mass of gas formed)
Although units for rate of reaction is usually mol/dm/s, we can still use volume of gas formed or mass of gas formed as they are proportional to concentration (unit for rate of reaction will be different in that case)

Question 16

What graph can you plot to deduce rate of reaction using continuous monitoring method

Answer 16

Plot a graph for:
Concentration against time
Volume against time (for gases)
Mass against time

Question 17

Draw an label a gas syringe

Answer 17

Ensure there is a reading and it is properly labelled

Question 18

What two apparatus can be used to measure volume of ga

Answer 18

Gas syringe
Measuring cylinder

Question 19

What are the physical quantities that can be monitored to measure rate of reaction

Answer 19

Concentration of a reactant or product
Gas volume of product
Mass of substance formed or decreasing mass (monitoring a reaction on a balance)

Question 20

How to calculate rate of reaction on a graph

Answer 20

Plot graph with collected data
Draw a line of best fit through the points
Draw a tangent on particular time asked to calculate
Calculate gradient of the formula dy/dx
To calculate initial rate draw a tangent where time=0 (where rate of reaction is fastest)

Question 21

Why is the initial rate of reaction the fastest

Answer 21

Highest concentration of particles at the start
More particles mean more frequent successful collisions in a given time

Question 22

What is the Maxwell Boltzmann distribution

Answer 22

The particles in a reaction undergo random collisions, in which energy is transferred between the colliding particles. As a result, there will be particles with different energies

Question 23

Label this maxwell Boltzmann curve

Answer 23

Question 24

What are the important points about Maxwell Boltzmann curve

Answer 24

The graph starts at the origin because there are no particles with zero(0) energy The graph does not touch the x axis at high energy because there will ALWAYS be some molecules with very high energies as there is no limit (ASYMPTOTE) Area under the curve=total number of molecules X axis=ENERGY Y axis = NO. OF MOLECULES The peak indicates the most probable energy

Question 25

What happens to Maxwell Boltzmann graph when temperature increases

Answer 25

It peaks to the right and lowers The value of Emp increases No. of molecules at Emp increases No of molecules with E >= Ea increases

Question 26

What happens to the Maxwell Boltzmann graph when temperature decreases

Answer 26

It peaks to the left and heightens The value of Emp decreases No. of molecules at Emp increases No. of molecules with E>=Ea decreases

Question 27

What happens to the Maxwell Boltzmann graph when there is fewer moles

Answer 27

The height of the peak decreases The value of Emp stays the same No. of molecules with Emp decreases No. of molecules with E>= Ea decreases Area under the curve also decreases

Question 28

What is a catalyst

Answer 28

A catalyst is a substance that increases the rate of a reaction but itself is unchanged at the end of the reaction.

Question 29

How does a catalyst work?

Answer 29

by providing an alternate route which has a lower activation energy than the uncatalysed route

Question 30

What effect does a catalyst have on the overall enthalpy change

Answer 30

Nooo effecttt

Question 31

Explain the two types of catalyst

Answer 31

Homogeneous- catalyst are in a different phase to the reactants heterogeneous - catalyst are in the same phase to the reactants.

Question 32

How can the use of catalyst in industrial processes be beneficial to the environment

Answer 32

They lower the energy demand for a reaction. Reaction can be done at lower temperatures and results in reduced CO2 emissions due to less fossil fuels being burned.

Question 33

What is the effect of a catalyst on Maxwell-Boltzmann curve (1st part)

Answer 33

Value of Emp stays the same No. of molecules with Emp stays the same No of molecules with E>= Ea increases Area under the curve stays the same

Question 34

What is the effect of a catalyst on Maxwell-Boltzmann curve (2nd part)

Answer 34

Catalyst increases the rate of reaction There really more molecules with energy greater than or equal to activation energy so higher frequency of successful collisions