Enthalpy Changes Flashcards

Enthalpy Concepts

• Enthalpy measures the heat energy involved in a chemical reaction.
• Enthalpy change quantifies the energy released or absorbed during a reaction and cannot be directly measured.
• Exothermic reactions release energy to the surroundings, indicated by a negative enthalpy change symbol (-∆H).
• Endothermic reactions absorb energy from the surroundings, denoted by a positive enthalpy change symbol (+∆H).

Activation Energy

• Activation energy is the minimum energy needed to initiate a reaction, primarily to break bonds.

Standard Conditions

• Enthalpy change under standard conditions is represented as ∆H^θ.
• Standard conditions include a pressure of 100 kPa, a temperature of 298 K, and the standard state of a substance (e.g., O₂ as a gas).

Types of Enthalpy Change

• Enthalpy change of reaction refers to the change occurring when molar quantities of reactants react together.
• Enthalpy change of formation is the change related to forming one mole of a compound from its elements.
• Enthalpy change of combustion involves the complete combustion of one mole of a substance.
• The enthalpy change of neutralization refers to the formation of one mole of water from a neutralization reaction between an acid and a base.

Neutralization Reactions

• The ionic equation for reactions between strong acids and bases is H⁺ + OH⁻ = H₂O.
• Since all strong acid-base reactions have the same ionic equation, the enthalpy change of neutralization is consistently -57 kJ/mol.

Calculating Enthalpy Changes

• To calculate the enthalpy change of neutralization (∆neutH), use the formula q (heat absorbed/released) divided by the moles of water produced.
• The general rule for calculating enthalpy changes in reactions is bond breaking - bond making, remembering to consider the signs.
• The formula to calculate enthalpy change of formation is ∆H2 - ∆H1.
• The formula for enthalpy change of combustion is ∆H1 - ∆H2.

Bond Energy

• Bond breaking is associated with an endothermic process, which requires energy input.
• Bond making is exothermic, releasing energy during bond formation.

Delta H Calculation

• The change in enthalpy (ΔH) is determined by subtracting the total energy of reactants from the total energy of products, resulting in either a positive or negative value.

Explore the fundamental concepts of enthalpy changes in chemical reactions through these flashcards. Each card provides a key term and its definition, aiding in the understanding of exothermic reactions and enthalpy calculations.