Rate of reaction Chapter Notes | Chemistry for GCSE/IGCSE - Year 11 PDF Download

 Page 1


Rate of reactions
? Rate of reaction = Quantity of products formed/Time taken(s)
Quantity of reactants used / Time taken(s)
? Rate is a measure of the change that happens in a single unit of time
? Unit
? ? Mass  gram
? ? Time  seconds
? ? Volume  cm2
? Mass of reactant will have negative slope as it is
being used up
? Volume of products formed will be a positive slope
as more and more is being produced
? Faster the reaction, the steeper the curve
? When the reaction is over, the curve goes flat
Graph questions
? Why is the slope of the graph steeper at the beginning of the reaction?
? This is because there are more particles available in the reaction leading to more particles
passing the activation barrier
? What happens to the graph as the reaction progresses?
? The graph gets less steep because there are less particles available leading to less
effective collisions leading to less particles passing the activation energy
? Why is the graph constant after a while?
? This is because all the reactants are used up therefore no collisions can take place so no
reaction takes place
? Minimum amount of energy required for particles to react is called activation energy
? Rate of reaction depends on-
? Frequency of collisions between particles
? The energy by which they collide
Page 2


Rate of reactions
? Rate of reaction = Quantity of products formed/Time taken(s)
Quantity of reactants used / Time taken(s)
? Rate is a measure of the change that happens in a single unit of time
? Unit
? ? Mass  gram
? ? Time  seconds
? ? Volume  cm2
? Mass of reactant will have negative slope as it is
being used up
? Volume of products formed will be a positive slope
as more and more is being produced
? Faster the reaction, the steeper the curve
? When the reaction is over, the curve goes flat
Graph questions
? Why is the slope of the graph steeper at the beginning of the reaction?
? This is because there are more particles available in the reaction leading to more particles
passing the activation barrier
? What happens to the graph as the reaction progresses?
? The graph gets less steep because there are less particles available leading to less
effective collisions leading to less particles passing the activation energy
? Why is the graph constant after a while?
? This is because all the reactants are used up therefore no collisions can take place so no
reaction takes place
? Minimum amount of energy required for particles to react is called activation energy
? Rate of reaction depends on-
? Frequency of collisions between particles
? The energy by which they collide
? ? Collisions are measured by  per unit time/ per unit volume / per unit area
? The rate of a reaction depends on how many successful collisions there are per unit time
? If particles collide with less energy than the activation energy, they will not react and just
bounce off each other(ineffective collisions)
? Collision theory
? Particles must collide with each other
? The collisions must have enough energy to be successful. In other words, enough energy to
break bonds to allow reaction to occur
Changing the rate of reaction
? Concentration
? In dilute acid, there are not so many particles per unit volume, so there is a less chance of
an effective collision
? When acid is more concentrated, there are more particles per unit volume, so there is a
higher chance of successful collisions per unit time therefore the reaction becomes
faster.
? Temperature
? A higher temperature means more energy which causes the particles to collide more often
which leads to more effective collisions which leads to more particles passing the
activation barrier which means a faster rate of reaction
? Pressure
? It will not affect the reaction unless all the products are in gaseous state as pressure only
affects gases
? When you increase pressure on 2 reacting gases, it means gas molecules per unit volume
therefore there is greater chance of effective collisions therefore the rate of reaction
increases
? Surface area
? If a solid is split into multiple pieces, the surface area increases, this means an increased
area for the reactant particles to collide with each other
? The smaller the pieces, the larger the surface area. This means more collisions and a
greater chance of reaction
? A catalyst alters the rate of reaction by providing an alternative pathway and lowering the
activation energy
? This allows more effective collisions and therefore rate of reaction increases
Page 3


Rate of reactions
? Rate of reaction = Quantity of products formed/Time taken(s)
Quantity of reactants used / Time taken(s)
? Rate is a measure of the change that happens in a single unit of time
? Unit
? ? Mass  gram
? ? Time  seconds
? ? Volume  cm2
? Mass of reactant will have negative slope as it is
being used up
? Volume of products formed will be a positive slope
as more and more is being produced
? Faster the reaction, the steeper the curve
? When the reaction is over, the curve goes flat
Graph questions
? Why is the slope of the graph steeper at the beginning of the reaction?
? This is because there are more particles available in the reaction leading to more particles
passing the activation barrier
? What happens to the graph as the reaction progresses?
? The graph gets less steep because there are less particles available leading to less
effective collisions leading to less particles passing the activation energy
? Why is the graph constant after a while?
? This is because all the reactants are used up therefore no collisions can take place so no
reaction takes place
? Minimum amount of energy required for particles to react is called activation energy
? Rate of reaction depends on-
? Frequency of collisions between particles
? The energy by which they collide
? ? Collisions are measured by  per unit time/ per unit volume / per unit area
? The rate of a reaction depends on how many successful collisions there are per unit time
? If particles collide with less energy than the activation energy, they will not react and just
bounce off each other(ineffective collisions)
? Collision theory
? Particles must collide with each other
? The collisions must have enough energy to be successful. In other words, enough energy to
break bonds to allow reaction to occur
Changing the rate of reaction
? Concentration
? In dilute acid, there are not so many particles per unit volume, so there is a less chance of
an effective collision
? When acid is more concentrated, there are more particles per unit volume, so there is a
higher chance of successful collisions per unit time therefore the reaction becomes
faster.
? Temperature
? A higher temperature means more energy which causes the particles to collide more often
which leads to more effective collisions which leads to more particles passing the
activation barrier which means a faster rate of reaction
? Pressure
? It will not affect the reaction unless all the products are in gaseous state as pressure only
affects gases
? When you increase pressure on 2 reacting gases, it means gas molecules per unit volume
therefore there is greater chance of effective collisions therefore the rate of reaction
increases
? Surface area
? If a solid is split into multiple pieces, the surface area increases, this means an increased
area for the reactant particles to collide with each other
? The smaller the pieces, the larger the surface area. This means more collisions and a
greater chance of reaction
? A catalyst alters the rate of reaction by providing an alternative pathway and lowering the
activation energy
? This allows more effective collisions and therefore rate of reaction increases
R e d o x
R e d u cti on O x i d a t i on
Loss of oxygen Gain of oxygen
Gain of hydrogen Loss of hydrogen
Gain of electrons Loss of electrons
? ? Reactants which undergo oxidation  reducing agent
? ? Reactants which undergoes reduction  oxidizing agent
? Oxidation number /state
? The total number of electrons lost or gained for a chemical bond to be formed
? Rules of assigning oxidation number
? The oxidation number of an atom by itself is zero
? The oxidation number of any monatomic ion is equal to its change
? The oxidation number of elements in a compound are written per atom
? The sum of the oxidation number in a compound is zero
? The sum of the oxidation number in a polyatomic ion is equal to the ions change
? Oxidation numbers to remember
¦ ? Elements in group 1  +1
¦ ? Elements in group 2  +2
¦ ? Aluminium  +3
¦ ? Fluorine  -1
¦ ? Hydrogen  +1
¦ ? Oxygen  -2
? Oxidation number sign is written before the number while the ion charge is written after the
number
? ? Oxidation  the oxidation number of 1 or more
? ? Reduction  a oxidation number of -1 or less
? Oxidation number of NO
? X -2 = 0
X = 2
Page 4


Rate of reactions
? Rate of reaction = Quantity of products formed/Time taken(s)
Quantity of reactants used / Time taken(s)
? Rate is a measure of the change that happens in a single unit of time
? Unit
? ? Mass  gram
? ? Time  seconds
? ? Volume  cm2
? Mass of reactant will have negative slope as it is
being used up
? Volume of products formed will be a positive slope
as more and more is being produced
? Faster the reaction, the steeper the curve
? When the reaction is over, the curve goes flat
Graph questions
? Why is the slope of the graph steeper at the beginning of the reaction?
? This is because there are more particles available in the reaction leading to more particles
passing the activation barrier
? What happens to the graph as the reaction progresses?
? The graph gets less steep because there are less particles available leading to less
effective collisions leading to less particles passing the activation energy
? Why is the graph constant after a while?
? This is because all the reactants are used up therefore no collisions can take place so no
reaction takes place
? Minimum amount of energy required for particles to react is called activation energy
? Rate of reaction depends on-
? Frequency of collisions between particles
? The energy by which they collide
? ? Collisions are measured by  per unit time/ per unit volume / per unit area
? The rate of a reaction depends on how many successful collisions there are per unit time
? If particles collide with less energy than the activation energy, they will not react and just
bounce off each other(ineffective collisions)
? Collision theory
? Particles must collide with each other
? The collisions must have enough energy to be successful. In other words, enough energy to
break bonds to allow reaction to occur
Changing the rate of reaction
? Concentration
? In dilute acid, there are not so many particles per unit volume, so there is a less chance of
an effective collision
? When acid is more concentrated, there are more particles per unit volume, so there is a
higher chance of successful collisions per unit time therefore the reaction becomes
faster.
? Temperature
? A higher temperature means more energy which causes the particles to collide more often
which leads to more effective collisions which leads to more particles passing the
activation barrier which means a faster rate of reaction
? Pressure
? It will not affect the reaction unless all the products are in gaseous state as pressure only
affects gases
? When you increase pressure on 2 reacting gases, it means gas molecules per unit volume
therefore there is greater chance of effective collisions therefore the rate of reaction
increases
? Surface area
? If a solid is split into multiple pieces, the surface area increases, this means an increased
area for the reactant particles to collide with each other
? The smaller the pieces, the larger the surface area. This means more collisions and a
greater chance of reaction
? A catalyst alters the rate of reaction by providing an alternative pathway and lowering the
activation energy
? This allows more effective collisions and therefore rate of reaction increases
R e d o x
R e d u cti on O x i d a t i on
Loss of oxygen Gain of oxygen
Gain of hydrogen Loss of hydrogen
Gain of electrons Loss of electrons
? ? Reactants which undergo oxidation  reducing agent
? ? Reactants which undergoes reduction  oxidizing agent
? Oxidation number /state
? The total number of electrons lost or gained for a chemical bond to be formed
? Rules of assigning oxidation number
? The oxidation number of an atom by itself is zero
? The oxidation number of any monatomic ion is equal to its change
? The oxidation number of elements in a compound are written per atom
? The sum of the oxidation number in a compound is zero
? The sum of the oxidation number in a polyatomic ion is equal to the ions change
? Oxidation numbers to remember
¦ ? Elements in group 1  +1
¦ ? Elements in group 2  +2
¦ ? Aluminium  +3
¦ ? Fluorine  -1
¦ ? Hydrogen  +1
¦ ? Oxygen  -2
? Oxidation number sign is written before the number while the ion charge is written after the
number
? ? Oxidation  the oxidation number of 1 or more
? ? Reduction  a oxidation number of -1 or less
? Oxidation number of NO
? X -2 = 0
X = 2
? ? CO2 + C  2CO
? ? Reduction = CO2  2CO
? ? Oxidation = C  2CO
? Colour changes
? Potassium manganate
¦ Reducing agent turns purple to colourless
? Potassium iodide
¦ Oxidising agent turns colourless to red-brown
? Potassium dichromate
¦ Reducing agent turns from orange to green