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Flashcards in Rates Of Reaction Deck (40):

What is the rate of reaction?

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


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


How does the reaction proceed according to the graph?


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


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


What factors affect the rate of reaction?

Nature of reactants
Particle size


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


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


What is needed for a dust explosion to occur?

Enclosed space
Source of ignition


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


How does temperature affect the rate of reaction?

The higher the temperature, the faster the reaction.


What is a catalyst?

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


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


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


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


Name one element used as a catalyst in a catalytic converter

Palladium, Platinum, Rhodium


What type of catalysis is involved in a catalytic converter?

Heterogenous, adsorption


What is activation energy?

The minimum energy which colliding molecules need before they can react


Give an example of a reaction involving a named catalyst

2H2O2 - 2H2O + O2
Catalyst -MnO2


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


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


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


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


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


What are features of catalysts?

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


Suggest how catalysts can differ

Greater/smaller surface area


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

Low concentration
Low temperature


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

Platinum wire glows
Flame pops


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



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

Adsorption surface


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.


Give one way that catalysts increase the rate of reaction

Lower activation energy


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



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

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


When do you use curvey graph

-manganese dioxide and marble chips


Explain effective collisions

When particles reach activation energy and react to form product


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



Give another example of heterogenous catalysis

Decomposition of Hydrogen peroxide


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


Why does the rate of chemical reactions decrease over time?

Concentrations decrease as reactants used up


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