5. Chemical Energetics (Cambridge IGCSE Chemistry 0620 for 2023, 2024 & 2025)

Summary

This 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

00:00

📚 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.

05:00

🌡️ 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.

10:02

🔧 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.

Keywords

💡Exothermic reaction

An exothermic reaction is a type of chemical reaction that releases heat energy to the surroundings, resulting in an increase in temperature. In the video, exothermic reactions are described as those where the energy of the reactants is higher than that of the products, leading to heat release. An example given is how exothermic reactions have a negative enthalpy change (ΔH).

💡Endothermic reaction

An endothermic reaction is a chemical reaction that absorbs heat energy from its surroundings, causing a decrease in temperature. In the video, it is explained that these reactions occur when the energy of the products is higher than that of the reactants, requiring energy to be absorbed. Endothermic reactions have a positive enthalpy change (ΔH).

💡Activation energy

Activation energy (Ea) is the minimum amount of energy that colliding particles must have in order to initiate a chemical reaction. The video shows this concept as the 'spike' or 'bump' in the reaction pathway diagram, representing the energy barrier that must be overcome for a reaction to proceed.

💡Enthalpy change (ΔH)

Enthalpy change (ΔH) refers to the amount of thermal energy transferred during a reaction, whether it's released or absorbed. In the video, it's explained that ΔH is negative for exothermic reactions and positive for endothermic reactions. It is a key concept in determining whether a reaction releases or absorbs heat.

💡Reaction pathway diagram

A reaction pathway diagram, also known as an energy level diagram, visually represents the energy levels of reactants and products during a chemical reaction. The video illustrates how these diagrams depict the activation energy and show whether a reaction is exothermic (products lower in energy) or endothermic (products higher in energy).

💡Bond energies

Bond energies represent the amount of energy required to break one mole of a specific bond in a molecule. The video uses bond energies to calculate the enthalpy change of reactions by comparing the total energy required to break bonds in the reactants and the energy released when new bonds are formed in the products.

💡Energy in

In the context of the video, 'energy in' refers to the total bond energies of the bonds that need to be broken in the reactants during a chemical reaction. This energy is absorbed to break bonds, and it plays a critical role in determining whether a reaction is endothermic or exothermic based on its comparison to the 'energy out'.

💡Energy out

'Energy out' is the total bond energy released when new bonds are formed in the products of a reaction. The video explains how this concept is essential in calculating the enthalpy change (ΔH) by comparing the energy released during bond formation to the energy absorbed during bond breaking.

💡Bond making

Bond making is described as an exothermic process, where energy is released when new chemical bonds are formed. The video highlights this process as the source of energy release in exothermic reactions, contributing to the overall negative enthalpy change.

💡Bond breaking

Bond breaking is an endothermic process, requiring energy to be absorbed in order to break chemical bonds in the reactants. The video emphasizes that this energy intake is essential for endothermic reactions, as it increases the energy level of the system, resulting in a positive enthalpy change.

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

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