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Endothermic: A reaction that absorbs energy from the surroundings, resulting in a positive enthalpy change (ΔH) .●

Exothermic: A reaction that releases energy to the surroundings, resulting in a negative enthalpy change (ΔH) .●

Enthalpy Changes (ΔH): The heat energy exchange in a reaction at constant pressure .○

A negative ΔH indicates an exothermic reaction (energy released).○

A positive ΔH indicates an endothermic reaction (energy absorbed).●

Assumptions in Calorimetry: To measure enthalpy changes, calorimetry experiments are conducted under certain assumptions to simplify calculations .○

Assumption 1: All heat was transferred entirely to/from the "surroundings" you measured (i.e., no heat loss to the environment) .○

Assumption 2: In solutions, have water's exact density & specific heat .●

Standard Enthalpy Changes: The enthalpy change when a reaction occurs under standard conditions (298 K, 1 atm pressure) .○

Standard enthalpy changes are often represented with a superscript "o", such as ΔH° .●

Hess's Law: The total enthalpy change for a reaction is independent of the pathway taken. It only depends on the initial and final states .○

This allows us to calculate enthalpy changes for reactions that are difficult to measure directly.○

Equation: ΔH (total) = Σ ΔH (each step)●

Bond Enthalpies: The average energy required to break one mole of a specific bond in a gaseous molecule .○

Bond enthalpies can be used to estimate enthalpy changes for reactions by considering the bonds broken and formed.○

Equation: ΔH = Σ(bond enthalpies of reactants) - Σ(bond enthalpies of products)●

Enthalpy of Combustion (ΔHc): The enthalpy change when one mole of a substance completely combusts (reacts with excess oxygen) under standard conditions .○

Equation: ΔH_c = Σ(ΔH_f products) - Σ(ΔH_f reactants)●

Enthalpy of Formation (ΔHf): The enthalpy change when one mole of a substance is formed from its elements in their standard states .○

The ΔH_f of an element in its standard state is zero .○

Equation: ΔH_f = Σ(ΔH_f products) - Σ(ΔH_f reactants)●

Covalent Bond Enthalpy: The energy required to break one mole of a covalent bond between two atoms in the gaseous state .●

Atomization Energy: The energy required to convert one mole of a substance in its standard state into gaseous atoms .○

Always endothermic (+) .●

Ionization Energy (IE): The energy required to remove one mole of electrons from one mole of gaseous atoms, forming gaseous ions .○

Always endothermic (+) .○

The first ionization energy (IE₁) refers to the removal of the first electron, the second ionization energy (IE₂) refers to the removal of the second electron, and so on .○

Successive ionization energies increase because it becomes harder to remove electrons as the positive charge of the ion increases .○

Equation: X(g) → X⁺(g) + e^-●

Electron Affinity (EA): The energy change when one mole of electrons is added to one mole of gaseous atoms, forming gaseous ions .○

Can be exothermic (-) or endothermic (+) .○

Equation: X(g) + e^- → X^-(g)●

Lattice Enthalpy: The energy change when one mole of an ionic lattice is formed from its gaseous ions .○

Always very exothermic (-) because it involves the formation of strong ionic bonds .●

Born-Haber Cycle: An enthalpy cycle that represents the formation of an ionic compound from its elements in their standard states. It includes steps such as atomization, ionization, electron affinity, and lattice enthalpy .○

The Born-Haber cycle can be used to calculate lattice enthalpies indirectly.

Combustion & Fuels Terms & Definitions●

Combustion: A chemical reaction in which a substance reacts rapidly with oxygen, releasing heat and light . Typically involves the formation of oxides as products .●

Incomplete Combustion: Combustion that occurs with a limited oxygen supply .○

Produces less energy than complete combustion .○

May form carbon monoxide (CO) or soot (C) in addition to carbon dioxide (CO₂) .●

Fossil Fuels: Carbon-based fuels formed from the remains of ancient organisms over millions of years .○

Examples: Coal, petroleum (crude oil), natural gas .○

Advantages:■

Cheap and plentiful (for now).■

Easily transported through pipelines .■

High energy density .○

Disadvantages:■

Nonrenewable resources .■

Combustion releases greenhouse gases (CO₂), contributing to global warming .■

Can release sulfur dioxide (SO₂) leading to acid rain .■

Extraction and processing can be environmentally damaging .●

Biofuels: Fuels derived from recently living organisms (plant or animal matter) .○

Examples: Ethanol, biodiesel .○

Advantages:■

Renewable source of energy .■

Produce fewer greenhouse gas emissions compared to fossil fuels (though not carbon neutral) .○

Disadvantages:■

Can compete with food crops for land use .■

May require significant energy for processing .■

Still produce some greenhouse gases during production and combustion .●

Fuel Cells: Electrochemical devices that convert chemical energy directly into electrical energy .○

Fuel cells are highly efficient and produce minimal pollutants, often just water .○

A common type is the hydrogen fuel cell, where hydrogen and oxygen react to produce water and electricity .

Greenhouse Gases●

Greenhouse Gases: Gases that trap heat in the atmosphere, contributing to the greenhouse effect and global warming .○

Examples: Carbon dioxide (CO₂), methane (CH₄), water vapor (H₂O), nitrous oxide (N₂O) .○

These gases absorb infrared radiation emitted from the Earth's surface, preventing heat from escaping back into space .