Energy and Chemical Change grade 11: Activation energy, heat of reaction, catalyst and MORE!

Summary

This video explores essential concepts in energy and chemical reactions, focusing on definitions and practical understanding. Key topics include enthalpy change (ΔH), activation energy, and the activated complex, with clear explanations of how energy is absorbed or released during reactions. It distinguishes exothermic reactions, which release energy, from endothermic reactions, which absorb energy, and explains the role of catalysts in speeding up reactions by lowering activation energy without being consumed. Using potential energy diagrams, the video illustrates these concepts visually, making it easier to grasp the processes behind energy changes and reaction rates in chemistry.

Takeaways

• 😀 Enthalpy change (ΔH) represents the energy change in a chemical reaction, measured in kJ/mol. It is calculated by subtracting the enthalpy of reactants from the enthalpy of products.
• 😀 Activation energy (Ea) is the minimum energy required to initiate a chemical reaction. It is the energy from reactants to the activated complex (the peak of the curve) on a potential energy diagram.
• 😀 The activated complex is an unstable, transition state that occurs between reactants and products in a chemical reaction. It is the point of maximum energy along the reaction pathway.
• 😀 Exothermic reactions release energy, resulting in products with lower energy than reactants. In these reactions, energy is released when bonds are formed.
• 😀 Endothermic reactions absorb energy, resulting in products with higher energy than reactants. In these reactions, energy is required to break bonds.
• 😀 A catalyst is a substance that speeds up a chemical reaction by lowering the activation energy, without being consumed or permanently altered in the process.
• 😀 The heat of reaction (enthalpy change, ΔH) can be determined by examining the difference in energy between the products and reactants in a potential energy diagram.
• 😀 The activation energy for a reaction can differ for the forward and reverse reactions, depending on whether the reaction is progressing from reactants to products or vice versa.
• 😀 In a potential energy diagram, a catalyst lowers the activation energy, providing an alternative pathway for the reaction that requires less energy input.
• 😀 The energy levels of reactants and products remain the same when a catalyst is used; only the activation energy is lowered, allowing the reaction to proceed more quickly.

Q & A

What is enthalpy change or heat of reaction (ΔH)?

Enthalpy change (ΔH), also known as heat of reaction, is the change in the total internal energy of all substances involved in a chemical reaction. It occurs when energy is transferred into or out of a system, often accompanied by heat transfer. It is measured in kJ per mole, and the change in enthalpy can be calculated using the formula: ΔH = Enthalpy of products - Enthalpy of reactants.

What is activation energy and how is it identified on a potential energy diagram?

Activation energy is the minimum energy needed for a chemical reaction to take place. It can be identified on a potential energy diagram as the energy difference between the reactants and the activated complex (the peak of the curve). It represents the energy required to break bonds and initiate the reaction.

What is an activated complex in a chemical reaction?

An activated complex is the unstable transition state between reactants and products in a chemical reaction. It occurs at the peak of the potential energy diagram. This state is unstable because the atoms are temporarily broken apart and do not remain in this configuration.

What is the difference between exothermic and endothermic reactions?

In exothermic reactions, energy is released, and the energy of the products is lower than that of the reactants. In endothermic reactions, energy is absorbed, and the energy of the products is higher than that of the reactants. Essentially, exothermic reactions release more energy than they absorb, while endothermic reactions absorb more energy than they release.

How does a catalyst affect a chemical reaction?

A catalyst increases the rate of a chemical reaction without being permanently altered by the reaction. It does so by lowering the activation energy, providing an alternative reaction pathway that requires less energy. As a result, reactions occur more quickly or efficiently.

What is the role of activation energy in determining the speed of a reaction?

The activation energy determines how quickly a reaction occurs. A higher activation energy means that more energy is required to start the reaction, which leads to a slower reaction. Conversely, a lower activation energy results in a faster reaction, as less energy is needed to initiate it.

What does the term 'exothermic' mean in terms of energy flow?

The term 'exothermic' refers to a reaction in which heat is released or exits the system. This happens because the energy released during the formation of products is greater than the energy absorbed during the breaking of bonds in reactants.

What is the difference between the forward and reverse activation energy on a potential energy diagram?

The forward activation energy is the energy needed to go from the reactants to the activated complex (the peak of the curve), while the reverse activation energy is the energy required to go from the products to the activated complex. These values can differ, with the reverse activation energy typically being higher for exothermic reactions.

How does the presence of a catalyst change the activation energy on a potential energy diagram?

A catalyst lowers the activation energy, which can be seen on a potential energy diagram as a lower peak for the reaction with the catalyst. The overall energy of the reactants and products remains the same, but the pathway requires less energy to reach the activated complex, speeding up the reaction.

Why is the activated complex considered unstable?

The activated complex is considered unstable because it is a high-energy state where bonds are partially broken and atoms are in transition. It does not represent a stable configuration, and it quickly reconfigures to form stable products as the reaction proceeds.