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.