Topic 9 Chem

Front 1

What is "chemical kinetics"

Back 1

Study of the rates of chemical reactions

Front 2

How is the rate of reaction found

Back 2

· measure rate of formation of a product

· or rate of removal of reactant

Usual procedure: measure a property of reaction mixture,eg vol&👀 how varies w/ time

Front 3

Graph of amount of product v time is steepest @ start, then slows down until it finally stops. Why does this happen?

Back 3

· Steepest at start as reaction is at fastest

· 1 reactant is being used up until none of it is left

Front 4

What does gradient @ any point of graph of amount/ concentration against time measure?

Back 4

Rate of reaction at that time

Front 5

Draw graph of how conc of reactant would change with time during a chem reaction

Back 5

Front 6

Draw graph of how vol of gas produced would change with time during a chem reaction

Back 6

Front 7

What's the technique used in recording of conc/ amount of product in the previous 2 graphs called

Back 7

Continuous monitoring

Front 8

How could we define rate of a chem reaction?

Back 8

· Amount product formed in given time (e.g. vol of gas (gas syringe) in t for reaction 2 finish)

Rate = volume (cm^3)/ time(s)= ..cm^3s^-1

· Amount reactant used up in given time

Front 9

What factors affect rate of chem reaction?

Back 9

SA (only solids)

Temp

Pressure (gaseous reactants)

Conc (reactions in solution)

Catalyst

Front 10

How does conc affect rate of chem reaction?

Back 10

· ⬆ conc ⬆ rate

· ⬆ particles per unit vol

· So more frequent collisions

Front 11

How catalyst affects rate of chem reaction

Back 11

· catalysts provide alternate reaction pathway

· w/ ⬇ Ea

· ⬆ particles have E > Ea

· ⬆ rate

Front 12

How does temp affect rate of chem reaction

Back 12

· ⬆ temp ⬆ rate

· Particles more KE

· ⬆ particles E > Ea

· Particles move ⬆ fast so + likely to collide

Front 13

Give the meaning of the term catalyst

Back 13

Substance that speeds up reaction rate w/out being chemically changed

Front 14

We often measure reaction rate @ very start of reaction. What's this called?

Back 14

initial rates method

Front 15

What must be kept constant in investigation of effect of conc on rate at which thiosulfate ions in solution react with H+ ions to form sulphur precipitate?

Back 15

· Vol sodium thiosulfate sol. so depth of sol. in flask constant (to ensure cross is obscured when same quantity of S(s) has precipitated)

· Vol & conc HCl

· Temp

Front 16

Suggest why mixture in flask should be poured into container of sat. sodium carbonate solution after each experiment

Back 16

reaction produce SO2

cause breathing problems, esp for asthmatics

SO2 is acidic oxide that reacts w/ alkaline sodium carb sol to form sodium sulfite

Sodium sulfite ionic, stays in solution

Front 17

Draw enthalpy profile for exo reaction

Back 17

Front 18

Draw enthalpy profile for endo reaction

Back 18

Front 19

What do all reactions need to take place

Back 19

Reactions only take place when collisions take place with sufficient energy, known as activation energy

Front 20

Define activation energy

Back 20

Minimum energy needed in a collision for a reaction to happen

Front 21

Draw enthalpy profile for exo reaction w/ & w/out catalyst

Back 21

Front 22

Draw enthalpy profile for exo reaction showing progress via an intermediate

Back 22

Front 23

Draw an energy distribution curve (i.e Maxwell-Boltzmann)

Back 23

Front 24

Do any particles have zero energy? So, where does the curve start?

Back 24

Origin

Front 25

Draw energy distribution curve for two diff temps, explain from graph why ⬆ temp ⬆ rate of reaction

Back 25

Front 26

Explain the effect of a catalyst on reaction rate, starting by drawing a maxwell-boltzmann distribution

Back 26

A catalyst speeds up reaction rate as provides alternate reaction pathway with lower Ea

Graph shows many more particles have E > Ea w/ catalyst than w/out

· as area under graph = no of particles & is larger

Front 27

What's heterogeneous catalysis

Back 27

Catalyst is in a diff phase (state) to the reactants or products

E.g. for

C2H4(g) + H2(g) -(Ni catalyst)-> C2H6(g)

Front 28

What is the use of heterogeneous catalysts in industry?

Back 28

Easy to separate from the products

Front 29

What's homogeneous catalysis

Back 29

The catalyst is in the same phase as reactants and products

Front 30

What's the use of a solid heterogeneous catalyst for industrial reactions in the gas phase?

Back 30

(Provides surface for reaction)

·gas molecules briefly held onto surfaceof solid

·where atoms of catalyst help them to react

· then product molecules break free & are carried away in the flow of gas

Front 31

Outline experiment to demonstrate that manganese(IV) oxide isn't used up in decomposition of H2O2

Back 31

· weigh mass of manganese (IV) oxide

· filter manganese(IV) oxide from water

· Leave filtrate to dry

· reweigh remaining solid

Front 32

How are catalysts economically beneficial in industrial reactions

Back 32

· makes reaction ⬆ productive by ⬆ yield of desired product & ⬇ waste

· (can use lower temps for same reaction)

· can often be recovered at end of reaction

Front 33

How does pressure affect rate of chem reaction

Back 33

⬆ pressure ⬆ rate

⬆ particles per unit volume

So more frequent collisions

Front 34

How does SA affect reaction rate

Back 34

⬆ SA, ⬆ rate

⬆ rate of collision between reactant particles