General Chemistry: Thermochemistry, Stoichiometry, and Chemical Reactions

Comprehensive vocabulary flashcards covering chemical equations, stoichiometry, limiting reactants, degrees of freedom, specific heat capacity, calorimetry, phase changes, bond energies, Hess's Law, standard enthalpies of formation, and prominent historical chemists.

Chemistry

The study of matter and the changes it undergoes.

Law of Conservation of Mass

The scientific law stating that mass (matter/atoms) is neither created nor destroyed during a chemical process.

Stoichiometric Coefficients

Numbers placed in front of chemical formulas in a balanced equation that apply to all atoms and subscripts in the molecule; coefficients are changed to balance equations, while subscripts must never be altered.

Limiting Reactant

The reactant that is completely consumed first in a reaction, thereby dictating and limiting the maximum amount of product that can be formed.

Excess Reactant

The reactant present in a quantity greater than necessary to react completely with the limiting reactant, leaving unreacted leftover substance after the reaction stops.

Chaulmoogric Acid

An extremely sticky natural substance used to treat leprosy that cannot be safely ingested or injected in its native form.

Alice Ball

The chemist who developed a chemical method to convert chaulmoogric acid into a water-stable ethyl ester, making it safely injectable for patients with leprosy.

Heat Capacity ($C$)

The amount of energy needed to raise the temperature of an entire object or system by $1\,^\text{o}\text{C}$, measured in $\text{J}/^\text{o}\text{C}$.

Specific Heat Capacity ($c$)

The heat capacity per gram or per mole of a substance ($\text{J}/(\text{g}\,^\text{o}\text{C})$ or $\text{J}/(\text{mol}\,^\text{o}\text{C})$), indicating how much heat energy is needed to raise its temperature.

Degrees of Freedom

The different ways gas molecules can store energy through physical movement, categorized into translations, rotations, and vibrations.

Translational Motion

Movement of an entire molecule through space from one point to another; it is the only type of motion that directly increases temperature ($T$).

Rotational Motion

The spinning motion of a molecule around an axis; energy channeled into rotation absorbs heat without directly increasing translational kinetic energy or temperature.

Vibrational Motion

The movement of bonded atoms oscillating toward and away from each other along their chemical bonds; absorbs heat energy without directly raising temperature.

Dr. Walter Lincoln Hawkins

A chemist who developed an essential stabilized plastic insulating sheath for telephone wires.

Calorimetry

The technique of measuring the heat energy exchanged between a system of interest (the 'event') and its surrounding medium (such as water), where $q_{\text{surr}} = -q_{\text{sys}}$.

Exothermic Process

A process in which heat energy exits the system into the surroundings ($q < 0$ or $\Delta H < 0$), typically feeling hot to the touch.

Endothermic Process

A process in which heat energy enters the system from the surroundings ($q > 0$ or $\Delta H > 0$), requiring energy input and feeling cold.

Enthalpy of Fusion ($\Delta H_{\text{fus}}$)

The amount of energy required to melt $1\,\text{mol}$ of a solid substance into a liquid at constant temperature.

Enthalpy of Vaporization ($\Delta H_{\text{vap}}$)

The amount of energy required to boil/vaporize $1\,\text{mol}$ of a liquid substance into a gas at constant temperature.

Potential Energy in Chemistry ($PE$)

The energy of position determined by Coulombic interactions ($PE = \frac{k q_1 q_2}{r}$), where strongly attracted particles close together possess lower, more negative potential energy.

Bond Length

The distance between bonded nuclei that maximizes electrostatic attraction before nuclear and electron repulsions dominate, corresponding to the lowest potential energy.

Bond Energy

The positive energy input required to break $1\,\text{mol}$ of a chemical bond ($+\text{kJ/mol}$); breaking bonds always requires energy input, while forming bonds releases energy.

Dr. Mary Blackburn

A nutritional scientist who conducted foundational research on nutrition and energy metabolism during human pregnancy.

Enthalpy of Reaction ($\Delta H_{\text{rxn}}$)

The overall heat energy absorbed or released during a chemical reaction at constant pressure, determined by the difference between product and reactant bond strengths.

Activation Energy ($E_{\text{a}}$)

The initial energy threshold ('spark') required to start a chemical reaction, even if the overall reaction is exothermic.

Hess's Law

The principle stating that if a reaction can be expressed as the sum of several steps, the overall $\Delta H$ of the reaction equals the sum of the $\Delta H$ values of those individual steps.

Standard State

The most stable, pure physical form of an element or substance at a pressure of $1\,\text{atm}$ and a temperature of $298\,\text{K}$ ($25\,^\text{o}\text{C}$).

Standard Enthalpy of Formation ($\Delta H_{\text{f}}^\text{o}$)

The heat energy released or consumed when $1\,\text{mol}$ of a substance is formed from its pure constituent elements in their most stable standard states ($\Delta H_{\text{f}}^\text{o} = 0\,\text{kJ/mol}$ for pure standard elements).

Dr. Luis Federico Leloir

The scientist who biochemically characterized the enzymatic pathway responsible for the breakdown of galactose in the human body.

Dr. Betty White Harris

A chemist known for her research on explosives synthesis and environmental remediation of energetic material contaminants.

TATB (Triaminotrinitrobenzene)

An extremely stable, heat-resistant explosive compound ($\text{C}_6\text{H}_6\text{N}_6\text{O}_6$) used in specialized military and mining applications.