5. Chemical Energetics (Cambridge IGCSE Chemistry 0620 for 2023, 2024 & 2025)
Summary
TLDRThis video from IGCS Study Body covers chemical energetics, specifically exothermic and endothermic reactions as outlined in the Cambridge IGCSE Chemistry syllabus. It explains how exothermic reactions release heat, while endothermic reactions absorb it. The video also details how to interpret energy level diagrams and calculate enthalpy changes using bond energies. A step-by-step example is provided using methane and chlorine, demonstrating how bond energy differences show whether a reaction is exothermic or endothermic. Viewers are encouraged to engage, like, and subscribe for more revision videos.
Takeaways
- 📚 The video covers topic five: chemical energetics from the Cambridge IGCSE syllabus.
- 🌡️ Chemical reactions can be exothermic (release heat) or endothermic (absorb heat) based on heat exchange with the surroundings.
- 🔥 Exothermic reactions transfer thermal energy to the surroundings, increasing temperature, while endothermic reactions absorb energy, lowering temperature.
- 📈 Reaction pathway diagrams illustrate the energy levels of reactants and products in chemical reactions.
- 💥 Exothermic reactions occur when the total energy of reactants is higher than that of products, releasing energy.
- ❄️ Endothermic reactions happen when the energy of the products is higher than the reactants, absorbing energy.
- ⚡ Activation energy is the minimum energy required for particles to collide and react.
- 🔺 Enthalpy change (ΔH) is negative for exothermic reactions and positive for endothermic reactions.
- 🧪 Bond-making is exothermic, while bond-breaking is endothermic, and the balance determines whether a reaction releases or absorbs energy.
- 🧮 The video demonstrates how to calculate enthalpy change using bond energies and shows that a methane-chlorine reaction is exothermic with a negative ΔH.
Q & A
What are exothermic and endothermic reactions?
-Exothermic reactions transfer heat energy to the surroundings, causing an increase in temperature, while endothermic reactions absorb heat energy from the surroundings, leading to a decrease in temperature.
How is energy represented in a reaction pathway diagram?
-In a reaction pathway diagram, the Y-axis represents the energy level. For exothermic reactions, the energy of the reactants is higher than that of the products, while for endothermic reactions, the energy of the products is higher than that of the reactants.
What is activation energy?
-Activation energy is the minimum energy required for colliding particles to react. It is represented by the initial spike or bump in the reaction pathway diagram.
How can the enthalpy change (ΔH) of a reaction be determined?
-The enthalpy change can be determined by calculating the difference between the total bond energies of the reactants (energy in) and the products (energy out). If the energy in is less than the energy out, ΔH is negative (exothermic reaction); if the energy in is greater than the energy out, ΔH is positive (endothermic reaction).
What does a negative enthalpy change indicate?
-A negative enthalpy change indicates that the reaction is exothermic, meaning it releases energy to the surroundings.
What is the difference between bond breaking and bond making in terms of energy?
-Bond breaking is an endothermic process that requires energy, while bond making is an exothermic process that releases energy.
How do you calculate the enthalpy change using bond energies?
-To calculate the enthalpy change, find the total bond energies of the reactants and the products, and then subtract the energy of the products from the energy of the reactants. The result will indicate whether the reaction is endothermic or exothermic.
In the provided example, why is the reaction exothermic?
-In the example, the energy needed to break the bonds (654 kJ/mol) is less than the energy released when new bonds are formed (769 kJ/mol), resulting in a negative enthalpy change of -115 kJ/mol, indicating the reaction is exothermic.
What does the displayed formula equation help with when calculating bond energies?
-The displayed formula equation helps identify the type and number of bonds involved in the reaction, allowing for an accurate calculation of bond energies.
How do energy levels in a reaction pathway diagram differ from bond energy calculations?
-In a reaction pathway diagram, energy levels refer to the total chemical energy of reactants and products, whereas bond energy calculations focus on the energy required to break bonds versus the energy released when forming new bonds.
Outlines
📚 Introduction to IGCSE Chemistry: Energetics
The video begins with an introduction to the IGCSE Study Bud channel, where viewers can revise chemistry topics from the Cambridge IGCSE syllabus. The focus of this video is on 'Chemical Energetics' (Topic 5). It explains how chemical reactions are classified as exothermic or endothermic based on their heat exchange with the surroundings. Exothermic reactions release heat, while endothermic reactions absorb heat, affecting the temperature of the surroundings. The concept of reaction pathway diagrams (energy level diagrams) is introduced to show energy changes in these reactions.
🌡️ Energy in Reactions: Exothermic vs. Endothermic Pathways
This section delves into exothermic and endothermic reaction pathways using energy level diagrams. In an exothermic reaction, the energy of the reactants is higher than that of the products, releasing energy to the surroundings, while in an endothermic reaction, the energy of the products is higher, meaning energy is absorbed from the surroundings. The importance of activation energy (Eₐ) is highlighted, which is the minimum energy required for reactants to undergo a reaction. The transfer of energy during a reaction is called the enthalpy change (ΔH), which is negative for exothermic and positive for endothermic reactions.
🔧 Calculating Enthalpy Changes Using Bond Energies
This paragraph explains the process of calculating enthalpy change using bond energies. The steps involve writing the balanced equation, calculating the total bond energies of the reactants (energy in) and products (energy out), and then finding the difference. If the energy in is less than the energy out, the reaction is exothermic with a negative enthalpy change. If the energy in is greater, the reaction is endothermic with a positive enthalpy change. The relationship between bond making (exothermic) and bond breaking (endothermic) is also explained, noting that reactions depend on the energy needed to break old bonds and form new ones.
🔍 Example: Calculating Enthalpy Change in a Reaction
An example of methane reacting with chlorine gas to form methyl chloride and hydrogen chloride is provided to demonstrate the calculation of enthalpy change. Bond energies are used to calculate the total energy required to break the bonds in the reactants and the energy released when bonds are formed in the products. The calculation reveals that the reaction is exothermic, with a negative ΔH of -115 kJ/mol. This showcases how to use bond energies to determine whether a reaction absorbs or releases energy.
🙌 Conclusion and Support for the Channel
The video concludes with a reminder to support the IGCSE Study Bud channel through YouTube’s Super Thanks feature. Viewers are encouraged to share their thoughts and suggestions in the comments section. A final message asks viewers to subscribe for more revision videos.
Mindmap
Keywords
💡Exothermic reaction
💡Endothermic reaction
💡Activation energy
💡Enthalpy change (ΔH)
💡Reaction pathway diagram
💡Bond energies
💡Energy in
💡Energy out
💡Bond making
💡Bond breaking
Highlights
Introduction to exothermic and endothermic reactions.
Exothermic reactions transfer heat energy to the surroundings, raising temperature.
Endothermic reactions absorb heat energy from the surroundings, lowering temperature.
Energy level diagrams show the energies of reactants and products in chemical reactions.
Exothermic reactions have higher reactant energy than product energy, releasing energy.
Endothermic reactions have higher product energy than reactant energy, absorbing energy.
Activation energy is the energy required to start a chemical reaction.
Enthalpy change (ΔH) is negative for exothermic reactions and positive for endothermic reactions.
Bond-making is exothermic, while bond-breaking is endothermic.
Enthalpy change is calculated by subtracting energy out (bonds formed) from energy in (bonds broken).
In exothermic reactions, less energy is needed to break bonds than is released when forming bonds.
In endothermic reactions, more energy is needed to break bonds than is released when forming bonds.
Distinguishing between total chemical energy in reactants/products and energy for bond-breaking/formation.
Example of calculating the enthalpy change for a reaction using bond energies.
The methane-chlorine reaction calculation shows an exothermic reaction with ΔH = -115 kJ/mol.
Transcripts
hi everyone welcome to igcs study body
where you can revise chemistry topics
from the Cambridge igcc
syllabus if you are enjoying our video
so far please don't forget to hit the
like button and subscribe to our
channel in this video you are going to
learn topic five chemical
energetics ch chemical reactions can be
categorized as either exothermic or
endothermic based on their heat exchange
with the
surroundings an exothermic reaction
transfers thermal or heat energy to the
surroundings leading to an increase in
the temperature of the
surroundings an endothermic reaction
takes in thermal or heat energy from the
surroundings leading to a decrease in
the temperature of the
surroundings so exothermic reactions
release heat energy while endothermic
reactions absorb heat
energy a reaction pathway diagram also
known as an energy level diagram shows
the energies of both the reactants and
final products in chemical
reactions an exothermic reaction occurs
when the total chemical energy of the
reactants is more than that of the
products resulting in the transfer of
this energy difference to the
surroundings in the form of
heat an endothermic reaction occurs when
the chemical energy of the reactants is
less less than that of the products
causing the transfer of this energy
difference from the surroundings to the
chemicals involved so heat is absorbed
from the
surroundings let's examine the
exothermic reaction pathway
diagram the Y AIS represents the energy
level where the energy of the reactants
is higher than that of the
products the initial Spike or bump in
the curve represents the activation
energy which is the energy required to
start the
reaction following this the energy level
of the products is lower than that of
the reactants indicating that the
difference in energy is released into
the
surroundings in in the case of an
endothermic reaction pathway the energy
of the products is higher than that of
the
reactants the curve represents the
activation energy following this the
energy level of the products is higher
than that of the reactants indicating
that additional energy is absorbed from
the surroundings to form the
products
activation energy or E Suba is the
minimum energy that colliding particles
must have in order to
react the transfer of thermal energy
during a reaction is called enthalpy
change symbol Delta h of the
reaction Delta H is negative for
exothermic reactions and positive for
endothermic
reactions let's learn how to calculate
the enthalpy change of a reaction using
Bond
energies first we Write the balanced
equation for the
reaction then find the energy in this is
the total Bond energies for all the
bonds in the
reactants Now find the energy out this
is the total Bond energies for all the
bonds in the
products finally calculate the enthalpy
change enthalpy change is equal to
energy taken in take away energy given
out therefore if the energy in is less
than the energy out the enthalpy or
energy change is negative so it's an
exothermic
reaction and if the energy in is greater
than the energy out the enthalpy change
is
positive so it is an endothermic
reaction Bond making is an exothermic
process and bond breaking is an
endothermic
process energy is released when bonds
are made in
products and energy is taken in to break
bonds apart in the
reactants whether a reaction absorbs or
releases energy depends on how much
energy it takes to break old bonds
compared to how much is released when
new bonds
form so if the energy needed to break
bonds is less than the energy released
then it's an exothermic reaction with a
negative enthalpy change
value if the energy needed to break
bonds is greater than the energy
released then it's an endothermic
reaction with a positive enthalpy change
value now please don't get confused with
these energy levels and the energy
levels on a reaction pathway diagram in
a reaction pathway diagram we are
talking about the total chemical energy
of the reactants and the products but
here we are talking about how much much
energy a reaction absorbs to break bonds
versus how much energy it releases when
new bonds form finally let's look at an
example showing how to calculate the
enthalpy change of a reaction using Bond
energies methane reacts with chlorine
gas to produce methy chloride and
hydrogen
chloride this is the equation for the
this
reaction use the bond energies given to
calculate the enthalpy change Delta H
for the reaction and show that the
reaction is
exothermic bond energy is the amount of
energy in KJ per mole which must be
supplied to break one mole of the
bond so this table shows the bond
Energies
the displayed formula equation for the
reaction helps to identify the type and
number of
bonds although methane has four CH bonds
the main chemical change involves
Breaking the Bond between carbon and
hydrogen in methane to form methy
chloride
ch3cl and hydrogen chloride
HCL since each methane molecule
contributes one carbon hydrogen bond to
the reaction we count only one Bond
broken for each CH4 molecule involved in
the
reaction so first we find the energy in
the Total Bond energies for all the
bonds in the reactants that is 1 CH Bond
plus one cl cl bond that adds up to a a
total of
654 KJ per
mole then find the energy out the Total
Bond energies for all the bonds in the
products that is 1 CCL Bond plus 1 HCL
bond that totals
769 KJ per
mole then we calculate the enthalpy
change which is energy taken in take
away energy given
out so
654 subtract
769 gives Min -
115 KJ per
mole since the enthalpy changed Delta H
is negative it shows that the reaction
is exothermic
that concludes topic five chemical
energetics are you enjoying our videos
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