Thermodynamics & Rates

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Enthalpy (ΔH)

Thermochemical Equations: Represent reactions with ΔH

Molar Enthalpy (ΔH/m): Heat change per mole of substance

Heat Transfer

ΔT: Change in temperature (°C)

c: Specific heat capacity (J/g°C)

m: Mass of substance (grams, g)

Q: Heat energy (Joules, J)

Equation: Q = mcΔT

Calorimetry

Calculate heat (Q) using Q = mcΔT

Measure temperature change (ΔT)

Mix reactants in the calorimeter

Procedure:

Types of Calorimeters: Coffee cup (constant pressure), bomb (constant volume)

Purpose: Measure heat absorbed or released during a chemical reaction

Factors Affecting Rates

Concentration: Higher concentration increases reaction rate

Catalysts: Lower activation energy, increase reaction rate

Surface Area: Greater surface area increases reaction rate

Temperature: Higher temperature increases reaction rate

Calculating Reaction Rates

Conductivity: Change in ionic concentration over time

pH: Change in acidity over time

Volume: Change in gas volume over time

Mass: Change in mass over time

Instantaneous Rate: Rate at a specific moment

Average Rate: Change in concentration over time

Hess' Law

Subtopic

Application: Combine steps to find overall ΔH

Principle: Total enthalpy change is the same regardless of the route taken

Energy Changes in Reactions

Energy Diagrams: Show energy changes during reactions

Endothermic Reactions: Net absorption of energy (e.g., photosynthesis)

Exothermic Reactions: Net release of energy (e.g., combustion)

Bond Breaking: Requires energy (endothermic)

Bond Formation: Releases energy (exothermic)