Chapter 8:Thermodynamics

Thermochemistry

The study of chemical reactions and processes that involve heat energy.

First Law of Thermodynamics

A formulation of the law of conservation of energy stating that the total energy of a system remains constant. It is expressed by the equation: \Delta U = q + w

Enthalpy of Reaction (\Delta H_{rxn})

The difference between the enthalpies of the products and the enthalpies of the reactants: \Delta H = H(\text{products}) - H(\text{reactants})

Endothermic vs. Exothermic Processes

1. Endothermic: Heat is absorbed by the system (\Delta H > 0).

2. Exothermic: Heat is released to the surroundings (\Delta H < 0).

Extensive vs. Intensive Properties

1. Extensive Property: Depends on the size or amount of substance (e.g., mass, volume, enthalpy).

2. Intensive Property: Does not depend on the size or amount (e.g., temperature, pressure, specific heat).

State Function

A property of a system determined by its current state, independent of the path taken to reach that state (e.g., temperature, pressure, volume, internal energy, and enthalpy).

Internal Energy Change in Gaseous Reactions

The relationship between internal energy (\Delta U) and enthalpy (\Delta H) for ideal gases: \Delta U = ext{\Delta} H - RT ext{\Delta} n

• From \text{\Delta} n = \text{moles of product gases} - \text{moles of reactant gases}

Specific Heat (s)

The amount of heat required to raise the temperature of one gram of a substance by one degree Celsius (units: \text{J/g} \cdot ^{\circ}\text{C}).

Heat Capacity (C)

The amount of heat required to raise the temperature of a given quantity of a substance by one degree Celsius (C = ms).

Bomb Calorimeter

A device used for constant-volume calorimetry to measure the heat of combustion. Since \Delta V = 0, the heat change (q_{v}) is equal to \Delta U.

Standard Enthalpy of Formation (\Delta H_{f}^{\circ})

The change in enthalpy when 1 mole of a substance in its standard state (1 \text{ atm}, 298.15 \text{ K}) is formed from its pure elements in their most stable forms.

Hess's Law

States that when reactants are converted to products, the change in enthalpy is the same regardless of whether the reaction occurs in one step or a series of steps.

Lattice Energy (U)

The energy required to completely separate one mole of a solid ionic compound into gaseous ions.

Heat of Hydration (\Delta H_{hydr})

The enthalpy change associated with gaseous ions entering water and becoming hydrated. It is usually a negative quantity.

Safe Dilution of Sulfuric Acid (H₂SO₄)

Because the process is highly exothermic, the concentrated acid should always be added slowly to water while stirring; never add water to concentrated acid to prevent splattering.