Rates Of Reaction Flashcards
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?
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
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 Concentration Temperature Particle size Catalyst
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
Oxygen
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
Specific
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
Purer
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
Methanal
H2O
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
Lead
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
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
- inc
- inc
- lowers
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
