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Flashcards in Rates Of Reaction Deck (59):
1

What is the rate of reaction?

The change in concentration of a reactant/product per unit time

2

As a reaction proceeds, it starts off at a fast pace and then it slows down, why?

After some time, the reactants become less concentrated as they are being used up and therefore the amount of reactants decreases

3

How does the reaction proceed according to the graph?
Curve

——————-
/
/
/

Steep initially indicated a fast rate and as the rate decreases it levels off
The reaction is complete when the graph levels off or has no slope

4

Two graphs of concentration, have to draw half conentration of reactant. Distinguish

Start of reaction, the half concentration is not as steep and will level off sooner and at a lower level

5

What factors affect the rate of reaction?

Nature of reactants
Concentration
Temperature
Particle size
Catalyst

6

How does the nature of reactants affect rate of reaction?

Ionic - fast due to the fact you don’t have to break bonds before new ones can be formed unlike covalent

7

How does particle size affect the rate of reactions?

The larger the surface area, the faster the rate of reaction will be. Smaller particles [powders] have a larger surface area and therefore are faster than large lumps

8

What is needed for a dust explosion to occur?

Enclosed space
Oxygen
Source of ignition

9

How does concentration affect the rate of reaction?

The higher the concentration, the faster the reaction and more product is formed in a shorter period of time.
Directly proportional

10

When you’re investing the effect of concentration on reaction rate -
Identify the pale yellow precipitate that obscures the cross on the sheet of paper

Colloidal sulfur

11

When you’re investigating the effect of concentration on reaction rate -
Describe the procedure for preparing the 0.08M solution of sodium thiosulfate from the 0.10M solution

0.1 = 100 cm3
Add 80cm3 of solution using burette
Make up until 100cm3 with deionised water

12

When you’re investing the effect of concentration on reaction rate -
Explain why the reciprocal of time [1/time] is used as a measure of the initial rate of the reaction?

Rate of reaction is inversely promotional to the time. When time increases, there is a decrease in rate

13

When you’re investing the effect of concentration on reaction rate -
Why are the concentration and the volume of HCL solution kept constant?

So that there is only one variable that changes - ensures fair experiment

14

How does temperature affect the rate of reaction?

The higher the temperature, the faster the reaction.

15

What is a catalyst?

It’s a substance that alters the rate of a chemical reaction without being used up in the reaction

16

Calcium carbonate [marble chips] reacts with hydrochloric acid according to the equation
CaCO3 + 2HCL + CO2 + H2O
Using simple experiments involving marble chips and HCL describe how you could demonstrate the effects of particle size

Equal masses of small particles [powder] and larger particles [lumps] were added to conical flask
HCL of equal volume and concentration from graduated cylinder is added
Time taken is noted - where there is no more gas bubbles, the vigour of the reaction is observed and small particles reacts quicker

17

Calcium carbonate [marble chips] reacts with hydrochloric acid according to the equation
CaCO3 + 2HCL + CO2 + H2O
Using simple experiments involving marble chips and HCL describe how you could demonstrate the effects of concentration

Equal volumes of HCL of different concentrations [80cm3 + fill rest with water]
Equal masses of equal sized particle [powder]
Time taken is noted - no gas bubbles, the vigour is observed and the higher concentration is faster

18

Catalytic converters are used in cars
Identify one reaction that is catalysed in the catalytic converter in a care and state one environmental benefit

2CO + 2NO = 2CO2 + N2
Benefit :
Decline in smog and acid rain
Decrease carbon monoxide emissions
Decline in killing of fish by NO
Decline in toxicity

19

Name one element used as a catalyst in a catalytic converter

Palladium, Platinum, Rhodium

20

What type of catalysis is involved in a catalytic converter?

Heterogenous, adsorption

21

What is activation energy?

The minimum energy which colliding molecules need before they can react

22

Identify the insoluble solid and colourless gas present in the reaction between sodium thiosulfate and dilute hcl

Insoluble solid : sulfur
Colourless gas : sulphur dioxide

23

Outline the experimental procedures you would follow in order to show the effect of concentration on reaction rate

Place a conical flask on a piece of paper marked with an X
Place fixed volume of a given concentration of thiosulfate in the flask
Add fixed volume of HCL to the flask and note the time taken for sulfur to obscure x, swirl conical flask, reaction is finished
Rate of reaction for concentration is inversely promotional to the time taken
Repeat the experiment with different concentrations

24

Outline the experimental procedures you would follow in order to show the effect of temperature on reaction rate

Place a conical flask on a piece of paper marked with an X
Place fixed volume of a given concentration of thiosulfate in the flask
Place in a water bath to keep temperature constant
Add fixed volume of HCL to the flask and note the time taken for sulfur to obscure x, swirl conical flask, reaction is finished
Rate of reaction for concentration is inversely promotional to the time taken
Repeat the experiment with different temperatures [water bath]

25

State the relationship between the rate of the reaction and the concentration of sodium thiosulfate

The rate of reaction is directly promotional to the concentration of the thiosulfate.

26

Explain why the rate of reaction increases with thiosulfate concentration

Increased concentration of thio means more molecules in a given molecule therefore more successful collisions and thus increase in rate of reaction

27

Give two reasons why the rate of reaction between sodium thiosulphate solution and dilute hydrochloric acid increases with temperature

Increased temperature
-inc kinetic energy of particles which results in a greater number of collisions and increase in number of successful collisions and therefore an increased rate of reaction
-inc average kinetic energy of molecules which results in more molecules reaching required activation energy for the reaction which results in increase rate of reaction

28

Give an example of a reaction involving a named catalyst

2H2O2 - 2H2O + O2
Catalyst -MnO2

29

Why is leaded petrol not suitable for a car fitted with a catalytic converter

It is a catalytic poison
Catalytic converter is made up of a large surface area and coated with three metal catalysts. Lead occupies their active sites and poisons them

30

In a reaction between zinc and hydrochloric acid it was observed that the rate of production of hydrogen decreased with time. Give two reasons why

As reaction goes on
-concentration of reactants decreases as they are being used up
-less reactants means less effective collisions to form products

31

What is homogenous catalysis and give an example

When the catalyst and reactants are in the same phase
Example - KMno4 reacts with Fe^2+ ions with catalyst Mn^2+. They are all in solution

32

What is heterogenous catalysis and give an example

When the catalyst and the reactants are in different phases
Example - methanol vapour reacts with oxygen gas with heated platinum as catalyst

33

What is autocatalysis and give an example

It’s when a product of the forward reaction catalyses the reaction
KMnO4 reacts with Fe^2+ ions and product Mn^2+ catalyses the reaction

34

What are features of catalysts?

They are not used up however may be physically changed
Specific
Can be reused
Can be poisoned
Act on forward and reverse directions of the same reactions

35

When you’re investigating the effect of concentration on reaction rate -
Describe a method you could use to determine when the same mass of sulfur had been formed in each run

X on a piece of Paper which ensures a fair test
When it’s no longer seen, sulfur has precipitated and shows same amount

36

Suggest how catalysts can differ

Greater/smaller surface area
Purer

37

How could you reduce the rate of reaction that takes place in solution

Low concentration
Low temperature

38

In the oxidation of methanol using platinum wire as catalyst -
State one observation made during this experiment

Platinum wire glows
Flame pops

39

In the oxidation of methanol using platinum wire as catalyst -
Identify two major products

Methanal
H2O

40

What term is usually used to describe the attachment of liquids or gaseous molecules to a solid surface?

Adsorption surface

41

Explain how adsorption surface affects rate of oxidation

Reacting substances adsorb onto surface of catalyst and this causes their concentration to build up and increases the rate of reaction.

42

In an experiment to investigate the temperature on the rate of reaction -
Describe and explain the change observed in the conical flask during the reaction

Sulfur precipitates to yellow smokey appearance

43

Investigation of effect of temperature on rate of reaction -
Explain how the change in the flask was used to obtain the reaction times

X under conical flask obscured - reaction finished

44

Describe the relationship of temperature vs 1/t

as temp increases, the number of colliding particles. At a point, it will reach threshold level of activation energy and therefore resulting in more effective collisions and explains the steepness

45

Investigation of effect of temperature on rate of reaction -
What would the effect on reaction times if the experiment were repeated using 0.025M of sodium thiosulfate rather than 0.05M

-find relationship
twice as slow
Why - Rate is directly proportional

46

Give one way that catalysts increase the rate of reaction

Lower activation energy

47

Name a substance that could poison the catalysts of the catalytic converter

Lead

48

Explain clearly why there is an almost instantaneous reaction /quick between sodium chloride and silver nitrate

BONDS
One metal and one non metal
IONIC BONDING - don’t need to break bonds to form new ones

49

If you were given sodium thiosulfate solutions of the following concentrations : 0.04M, 0.08M, 0.12M and 0.16M, describe how you would show that the rate of reaction is directly proportional to the concentration of sodium thiosulfate

-do method
-find 1/t
-plot vs concentration

50

When do you use curvey graph

-manganese dioxide and marble chips

51

Explain effective collisions

When particles reach activation energy and react to form product

52

In a reaction mixture, what effect if any does an increase in temperature have on
-no. of collisions
-effectiveness of collisions
-activation energy

-inc
-inc
-lowers

53

Give another example of heterogenous catalysis

Decomposition of Hydrogen peroxide

54

Why is the graph steepest at the beginning

At the beginning of the reaction is when the concentration is highest therefore there is more collisions

55

Why does the rate of chemical reactions decrease over time?

Concentrations decrease as reactants used up

56

Monitoring rate of production of oxygen and hydrogen perioxide -
How the reaction could be started at a time known

Add catalyst, stopper and start clock

57

Monitoring rate of production of oxygen and hydrogen perioxide -
How is the gas produced collected?

Delivery tube is connected to gas collection system

58

Monitoring rate of production of oxygen and hydrogen perioxide -
How the gas is measured

Inverted graduated cylinder

59

The oxidation of potassium sodium tartrate by hydrogen peroxide catalyses by cobalt (II) ions provides evidence for the intermediate formation theory. State observations and explain how they prove theory

Pink - green - new substance made
Back pink - intermediate is formed
Bubbling/fizzing - means intermediate is reacting