Consider three reactions with different values of E_a and ΔE:
Reaction 1. E_a = 20 kJ>mol; ΔE = -60 kJ/mol
Reaction 2. E_a = 10 kJ>mol; ΔE = -20 kJ/mol
Reaction 3. E_a = 40 kJ>mol; ΔE = +15 kJ/mol
(c) Which reaction is the most endothermic, and which is the most exothermic?

Verified step by step guidance

1. Understand the terms: 'endothermic' means the reaction absorbs energy (ΔE is positive), and 'exothermic' means the reaction releases energy (ΔE is negative).
2. Identify the ΔE values for each reaction: Reaction 1 has ΔE = -60 kJ/mol, Reaction 2 has ΔE = -20 kJ/mol, and Reaction 3 has ΔE = +15 kJ/mol.
3. Compare the ΔE values: The most exothermic reaction will have the most negative ΔE value, and the most endothermic reaction will have the most positive ΔE value.
4. Determine the most exothermic reaction: Look for the reaction with the largest negative ΔE value.
5. Determine the most endothermic reaction: Look for the reaction with the largest positive ΔE value.

Key Concepts

Activation Energy (E_a)

Activation energy is the minimum energy required for a chemical reaction to occur. It represents the energy barrier that reactants must overcome to transform into products. A lower activation energy indicates that a reaction can proceed more easily, while a higher activation energy suggests a slower reaction rate. Understanding E_a is crucial for analyzing reaction kinetics and determining how temperature and catalysts can influence reaction rates.

Enthalpy Change (ΔE)

Enthalpy change (ΔE) refers to the heat content change during a chemical reaction at constant pressure. It indicates whether a reaction is exothermic (releases heat, ΔE < 0) or endothermic (absorbs heat, ΔE > 0). The magnitude of ΔE helps in understanding the energy dynamics of the reaction, which is essential for predicting the feasibility and direction of the reaction under given conditions.

Exothermic vs. Endothermic Reactions

Exothermic reactions release energy to the surroundings, resulting in a negative ΔE, while endothermic reactions absorb energy, leading to a positive ΔE. The classification of reactions as exothermic or endothermic is important for understanding energy flow in chemical processes. In the context of the given reactions, identifying which has the most negative ΔE indicates the most exothermic reaction, while the one with the highest positive ΔE indicates the most endothermic reaction.