IGCSE CHEMISTRY REVISION [Syllabus 7]- Chemical Reactions
Summary
TLDRThis IGCSE Chemistry revision video covers key concepts in chemical reactions, including the difference between chemical and physical changes, collision theory, and factors affecting reaction rates such as concentration, temperature, pressure, and particle size. It also explains reversible reactions and equilibrium, emphasizing how changes in conditions shift the position of equilibrium. The video introduces catalysts and their role in reactions, and concludes with an overview of redox reactions, explaining oxidation and reduction in terms of oxygen and electron transfer. The content is designed to aid exam preparation.
Takeaways
- 🔍 Chemical reactions differ from physical changes, where a physical change involves state changes like ice to water, while chemical changes occur at a molecular level.
- ⚡ The collision theory explains that for a chemical reaction to happen, particles must collide and have sufficient energy for the reaction to proceed.
- 🌡️ The rate of chemical reactions is influenced by factors like concentration, pressure, temperature, and particle size, each affecting collision rates and energy levels.
- 🔬 Higher concentration increases collision rates due to more particles being closer together, speeding up the reaction.
- 💨 Pressure affects gases by increasing particle collisions in a confined space, leading to faster chemical reactions.
- 🔥 Temperature impacts reaction rates by increasing particle energy and speed, leading to more frequent and forceful collisions.
- 🧊 Smaller particle sizes provide larger surface areas for collisions, which enhances reaction speed, especially in solids.
- 🔗 Catalysts, such as enzymes, speed up chemical reactions without being consumed, affecting both forward and reverse reactions without altering the reaction equilibrium.
- ⚖️ Equilibrium in reversible reactions occurs when the rate of the forward reaction equals the rate of the reverse reaction, stabilizing the concentrations of reactants and products.
- 🔄 Changes in conditions like concentration, temperature, and pressure can shift the equilibrium, favoring either the forward or reverse reaction depending on the situation.
Q & A
What is the difference between a chemical change and a physical change?
-A chemical change occurs at a molecular level when two or more molecules interact and form new substances, while a physical change involves changes in the state of matter without altering the chemical structure, such as ice turning into water.
What are the two key conditions for a chemical reaction to occur according to the collision theory?
-The two conditions are: 1) particles must collide, and 2) they must have sufficient energy during the collision for the reaction to occur.
How does concentration affect the rate of a chemical reaction?
-Higher concentration increases the number of particles in a given volume, leading to more frequent collisions, which increases the rate of the chemical reaction.
What is the effect of pressure on the rate of chemical reactions involving gases?
-Higher pressure increases the number of gas particles in a given space, leading to more collisions and an increased rate of reaction. Pressure only affects reactions involving gases.
How does temperature affect the rate of a chemical reaction?
-Higher temperature increases the energy and speed of particles, leading to more frequent collisions and higher energy, thus increasing the rate of reaction.
Why does smaller particle size increase the rate of chemical reactions in solids?
-Smaller particle size increases the surface area available for collisions, allowing more particles to react simultaneously, thus increasing the rate of the chemical reaction.
What is the role of catalysts in chemical reactions?
-Catalysts speed up chemical reactions without being consumed in the process. They do this by lowering the activation energy required for the reaction to occur.
What is a reversible reaction, and what happens at equilibrium?
-A reversible reaction is when the products of a reaction can react to form the original reactants. At equilibrium, the forward and reverse reactions occur at the same rate, so the concentrations of reactants and products remain constant.
How does the position of equilibrium shift when the concentration of reactants or products is changed?
-If the concentration of reactants increases, the equilibrium shifts to the right, producing more products. If the concentration of products increases, the equilibrium shifts to the left, producing more reactants.
What is a redox reaction, and how can it be defined in two ways?
-A redox reaction involves both reduction and oxidation. It can be defined by oxygen transfer (oxidation is the gain of oxygen, reduction is the loss of oxygen) or by electron transfer (oxidation is the loss of electrons, reduction is the gain of electrons).
Outlines
📘 Introduction to Chemical Reactions
This section introduces the basics of chemical reactions, distinguishing between chemical and physical changes. It explains that a physical change involves changes in the state of matter, like ice melting into water, whereas a chemical change happens at the molecular level when two or more molecules interact. The collision theory is introduced, emphasizing that particles must collide with sufficient energy for a reaction to occur. Factors like temperature, pressure, and concentration affect the collision rates and therefore the rate of reaction.
📈 Factors Influencing Reaction Rates
This paragraph delves into how different factors impact the rate of a chemical reaction. Concentration is explained as the number of particles in a given volume, with higher concentrations increasing the likelihood of particle collisions. Similarly, high pressure increases the number of particles in a given space, raising collision rates. Temperature is also a key factor, as higher temperatures increase both particle energy and collision rates. Additionally, smaller particle sizes provide larger surface areas for collisions, speeding up reactions. The concept of catalysts, which speed up reactions without being consumed, is briefly introduced.
🔄 Reversible Reactions and Equilibrium
Reversible reactions are introduced, where products can revert to reactants. The concept of equilibrium is explained as the point where the rate of the forward reaction equals the rate of the reverse reaction, causing concentrations of reactants and products to remain constant. The position of equilibrium can shift depending on environmental conditions. A shift to the right means more reactants are forming products, while a shift to the left indicates more products are breaking down into reactants. This paragraph sets the stage for exploring how conditions like concentration, temperature, and pressure affect equilibrium.
⚖️ Shifting Equilibrium: Effects of Concentration, Temperature, and Pressure
This section details how changes in conditions can shift the equilibrium of a reaction. An increase in product concentration shifts the equilibrium to the left, while a decrease shifts it to the right. Temperature changes are crucial—an increase favors the endothermic reaction (absorbing heat), while a decrease favors the exothermic reaction (releasing heat). Pressure affects equilibrium in gaseous reactions: higher pressure shifts equilibrium towards the side with fewer gas particles, and lower pressure shifts it towards the side with more particles. Catalysts do not affect the equilibrium position but speed up both the forward and reverse reactions.
🔋 Introduction to Redox Reactions
Redox (reduction-oxidation) reactions are introduced, highlighting two ways to define them: by oxygen transfer and electron transfer. Oxidation is defined as the gain of oxygen or the loss of electrons, while reduction is the loss of oxygen or the gain of electrons. An example involving copper oxide and hydrogen illustrates how reduction and oxidation occur simultaneously. Another example shows magnesium losing electrons (oxidation) and chlorine gaining electrons (reduction) in the formation of magnesium chloride. This section provides a foundational understanding of redox reactions, essential for further exploration of electrochemistry.
Mindmap
Keywords
💡Chemical Change
💡Physical Change
💡Collision Theory
💡Rate of Reaction
💡Concentration
💡Catalysts
💡Reversible Reaction
💡Equilibrium
💡Le Chatelier's Principle
💡Redox Reaction
Highlights
Differences between chemical and physical changes
Chemical reactions occur at the molecular level
Collision theory for chemical reactions
Two conditions for a chemical reaction to occur
Importance of collision rates and energy levels
How concentration affects the rate of chemical reactions
Pressure's role in chemical reaction rates
Temperature's impact on particle energy and collision rates
Particle size and surface area in chemical reactions
Catalysts and their effect on reaction rates
Reversible reactions and their characteristics
Equilibrium in reversible reactions
Position of equilibrium and its dependence on environmental conditions
Shift in equilibrium due to changes in concentration
Effect of temperature on equilibrium shifts
Impact of pressure on the position of equilibrium
Catalysts do not affect the position of equilibrium
Redox reactions defined by oxygen gain or loss
Redox reactions can also be viewed as electron gain or loss
Transcripts
hey guys welcome to another revision
video in IGCSE chemistry today we're
gonna be covering the fundamentals of
chemical reactions so without further
ado we'll begin so the first thing you
have to understand is the differences
between a chemical change in a physical
change a physical change relates to the
changes in the physical states of matter
for example eyes turning into water and
a chemical change occurs more molecular
level when two or more molecules
interact with one another taking a look
at chemical reactions in a bit more
detail we need to think about the
collision theory which states that two
conditions have to be met for a chemical
reaction to occur one of which being two
or more particles must collide the other
being that the particles when they do
collide have to have sufficient energy
in order for the reaction to occur so in
other words when two particles collide
but they don't have enough energy then
nor the reaction won't occur and
oppositely when they even if they have
enough energy when they don't collide
then of course then that's just not
going to work either so these two
conditions have to be met and this is
actually quite important when we take a
look at the rate of a chemical reaction
because a lot of conditions like
temperature pressure and all that sort
of stuff actually affect things like
collision rates of particles and you
know the energy levels and therefore
affecting how quickly the reaction
happens or in other words the rate of a
chemical reaction so this is exactly
what we're gonna be looking at now the
sir there's a couple of things the
concentration is basically how many
particles there are in a given volume
right so a higher concentration suggests
that there are more particles that are
closer to each other so therefore by
chance alone the rate of collision will
be higher and that means the rate of a
chemical reaction will thus be increased
as well pressure works exactly the same
way except that it's you know it's only
related to gases only so a high pressure
actually suggests that there are more
particles in a given space and therefore
again the collision rate will be higher
and therefore increasing the rate of a
chemical reaction the temperature ignore
the road size or in the temperature
if you think about it a higher
temperature will actually mean that the
particles the individual particles have
more energy but not only that because
they're traveling at a higher speed the
collision rate will also be higher as
well so both factors will be elevated
therefore increasing the rate of a
chemical reaction as well when we look
at particle size we are really only
referring to solids and it suggests that
a smaller particle size actually has a
lot larger surface area for collisions
to happen and therefore achieving a
higher rate of chemical reaction so I've
sort of diagrammatically represented
that here if you can see that the red
particles are trying to decompose the
the blue this blue block of solid into
its individual you know particles as
opposed you've got two options this big
block you can see that it's actually
quite inconvenient for the red ones to
act on because it cannot access the
middle atoms because it's sort of
surrounded by other blue particles
whereas if you were to separate the blue
particles into separate pieces you've
got a lot more area well the red
particles have a lot more area to work
on now to decompose this is the solid
and therefore the the rate of chemical
reaction will be a lot higher now when
we take a look at the at something
called catalysts so these are substances
that basically don't get used in the
chemical reaction but are there to
increase their rate and a bio enzymes
found in our bodies and that's an
example of a biological catalyst so
let's take a look at the concept of
reversible reactions so this is when
reactants form products so this is made
to be reactants sorry and the products
actually react to form back the
reactants for example it gives B to give
a a so a plus B gives C but C reacts
back to or decomposes back to give a and
B so in other words we can sort of
exemplify the reaction like so with this
double headed error so at some point in
a reversible reaction what will happen
as the rate of the forward reaction will
actually begin to equal exact
the rate of the reverse reaction so this
means that C is being formed at the same
rate as a and B is being formed because
a and B make C but C is informing a and
B at exactly the same rate what that
means therefore is that the
concentrations of all three of these
things ie the reactants and the products
will all remain constant and when this
happens this is called an equilibrium so
the concentrations of these individual
you know reactants and products and an
equilibrium is called the position of
equilibrium and we'll talk about that in
a bit more detail now so let's put that
up here again so the position of
equilibrium can actually shift okay
depending on how we alter the conditions
of the environment so when we talk about
a shift if we talked about it being a
shift to the right
it suggests that more of a and B as
getting used to make C this means that
the equilibrium concentrations of a and
B will decrease whereas this the
equilibrium concentration of C will
actually increase oppositely when we
talk about a shift to the lift it's
suggesting that more C is getting broken
down to make a and B so therefore the
concentration of products C goes down
where the concentrations of a and B will
inevitably elevate so depending on the
change in you know conditions the
equilibrium can either shift to the
right or to the left and we're gonna be
looking at that and a bit more detail
and this slide so for the sake of you
know the argument we're gonna say that a
plus B gives C again I've added some
extra information will say that the
forward reaction is exothermic whereas
the reverse reaction is endothermic and
this is important you'll you'll see why
later
but what's what's really really really
important to understand here is that the
position of equilibrium will always
always always shift in the direction to
oppose the change being imposed so you
know you'll understand what this means
as we go through each of these examples
for example concentration when we
increase the product concentration right
for example if we increase the
concentration of products C that will
shift the equilibrium to the lift
because
what so remember we're if we increase
the concentration of C the equilibrium
will try and oppose that change to
reduce the concentration and the way
that it can do that is shift the
equilibrium to the lift by producing
more a and B from C therefore decreasing
concentration of C exactly the same
thing if we were to forcefully decrease
the concentration of C and manipulate
the environment that way then the
equilibrium will actually shift to the
right as if to make more C so I hope
that makes sense and similar thing if we
were to increase the reactant
concentration for example the
concentration of a you would assume that
the equilibrium will actually shift to
the right in order to remove or reduce
the concentration of a and because we
just increased it and wants to oppose
that change and decrease it so that's
sort of how this whole thing works when
we talk about the temperature exactly
the same thing that's why I gave you
this extra information above if we were
to increase the temperature what the you
know what the reaction will do we'll try
to you know decrease the temperature so
it's so therefore it will favor the
endothermic reaction which means that
the reaction is taking in heat so it
will shift in this example it will shift
the equilibrium to the left if we were
to decrease the temperature it will
actually favor the exothermic reaction
because it's gonna try to increase the
temperature and you know by up it's
obviously opposing what we're doing so
it'll shift the equilibrium equilibrium
to the right if we were to do that now
when we talk about pressure I want you
to take a look at this diagram to the
right here because it's actually quite
important pressure can be pressure can
be basically defined by the the
individual gas molecules hitting against
the walls of the container and which
hits in so if you have more particles
and this given space then all there'll
be more collisions with the wall and
therefore the pressure will be higher if
you've got a smaller amount of particles
then there'll be less particles hitting
the walls and therefore less pressure so
picture really only is to do
gasses right so a high pressure suggests
that there is a lot more particles in
that given space compared to you know
lower pressures so if we were to
increase the pressure again the
equilibrium will shift to the side or it
will shift towards trying to decrease
the pressure and the way it can do that
is to favor the side that has lower
number of particles if you look at it
here the left left hand side in this
example has two particles but the
right-hand side only has one so
therefore it will actually shift the
equilibrium to the right in this
instance towards the side with a low
amount of particles because that gives
lower pressures if you were to decrease
the pressure it will be the opposite
it'll try to increase the pressure in
the way that it can do that is shift the
equilibrium position towards the side
that has more particles because more
particles means more particles hitting
against the walls of the container as
postie erratically and that gives rise
to higher pressures so in this case
decreasing the pressure will shift the
equilibrium position to the left and a
catalyst actually doesn't affect the
equilibrium at all so don't get tricked
by this and an exam it was only there
just increase the rate of reaction and
it increases the speed of both the four
and the reverse reaction it doesn't
affect the position so lastly we're
gonna be looking at the concept of redox
it's shortened full reduction in
oxidation and this can be demonstrated
in two different ways and births are
absolutely correct one is the oxygen
gained or lost right oxygen oxygen oxide
oxidation is the gain of oxygen whereas
reduction is the loss of oxygen so in
this example to the right here copper
oxide can be you can say that it's been
reduced because it goes from copper
oxide to copper therefore it's lost an
oxygen but if you think about it
hydrogen on the other hand has gained
oxygen so therefore it's you can say
that the hydrogen has been oxidized
another way of looking at redox is the
electron gain or loss so oxidation is
defined as the loss of electrons and
reduction is the gain of electrons so if
you look at this example here magnesium
at a2 chlorine giving magnesium chloride
you can see that there's no absolutely
no oxygen involved but there certainly
is some sort of electron transfer so
what we're gonna be looking at is how
magnesium right the the atom has evolved
or change itself into the ionic form in
this ionic structure of magnesium
chloride so if you take a look at it
separately magnesium has actually lost
two electrons are and to form the
magnesium cation and therefore because
it's lost electrons it's said to have
been oxidized
whereas chlorine on the other hand the
molecule has gained electrons to become
the iron therefore it's an example of
reduction because it's again gained
electrons so I hope they hope you guys
found that helpful please visit my
website doublet or free exam Academy com
for more detailed notes and kind on the
topic otherwise please like share and
subscribe and I know that it's fairly
close to exams and also if you have any
further questions just comment and I
will try to answer thanks and I'll see
you in the next video
[Music]
関連動画をさらに表示
6. Chemical Reactions (Part 3) (3/5) (Cambridge IGCSE Chemistry 0620 for 2023, 2024 & 2025)
AQA 1.6 Equilibria REVISION
6. Chemical Reactions (Part 2) (2/5) (Cambridge IGCSE Chemistry 0620 for 2023, 2024 & 2025)
REAKSI REDOKS - SIMPLE KONSEP - KIMIA (Kursus Online Rp8.000 per BULAN : cek deskripsi)
Chemical Equilibrium Grade 12 Chemistry
Equilibrium: Crash Course Chemistry #28
5.0 / 5 (0 votes)