Chemistry: Mole Concept, Stoichiometry, and Thermochemistry Vocabulary

Vocabulary flashcards covering key terms and definitions from the collated Chemistry materials on mole concepts, stoichiometry, titrations, and thermochemistry.

Avogadro's Number

The number of constituent particles (atoms or molecules) contained in one mole of a substance, given as $6.02 \times 10^{23}$ or $6.022 \times 10^{23}\,mol^{-1}$.

Empirical Formula

The simplest whole-number ratio of atoms of each element present in a chemical compound.

Molecular Formula

The actual number of atoms of each element present in a single molecule of a chemical compound.

Relative Molecular Mass ($M_r$)

The mass of a molecule of a compound relative to carbon-12, calculated by summing the relative atomic masses of all constituent atoms, expressed in $g\,mol^{-1}$.

Exothermic Reaction

A chemical reaction or physical process that releases heat to its surroundings, resulting in a negative enthalpy change ($\Delta H < 0$) and a temperature increase in the surroundings.

Endothermic Reaction

A chemical reaction or physical process that absorbs heat energy from its surroundings, resulting in a positive enthalpy change ($\Delta H > 0$) and a drop in temperature of the reaction mixture.

Volumetric Flask

A calibrated piece of laboratory glassware used to prepare a standard solution containing a precise volume of liquid when filled to its calibration mark.

Volumetric Pipette

A calibrated piece of glass equipment designed to measure and deliver a highly accurate fixed volume (aliquot) of a liquid solution.

Burette

A graduated vertical glass tube with a tap at the bottom, used in titrations to accurately deliver variable volumes of liquid.

Concordant Titres

Titration volume readings that lie within a close specified precision range (typically within $0.2\,mL$ of each other) and are averaged to determine the exact end point.

Standard Solution

A solution of accurately known concentration, prepared by dissolving a precisely weighed quantity of solute and making up to a exact volume in a volumetric flask.

Specific Heat Capacity ($c$)

The quantity of heat energy needed to raise the temperature of one gram of a substance by one degree Celsius, equal to $4.18\,J\,g^{-1}\,^\circ\text{C}^{-1}$ for water.

Molar Enthalpy of Solution ($\Delta H_{\text{sol}}$)

The heat energy absorbed or released per mole of a solute when it dissolves completely in a solvent, calculated using $\Delta H_{\text{sol}} = \frac{q}{n}$.

Systematic Error in Calorimetry

A consistent error—such as unmeasured heat loss to the surrounding air, container, or thermometer—that leads to an underestimation of temperature change ($\Delta T$) and calculated heat ($q$).

Energy Density per Gram

The amount of thermal energy released per unit mass of fuel during complete combustion, calculated as molar enthalpy of combustion divided by molar mass ($kJ\,g^{-1}$).

Energy Density per Litre

The amount of thermal energy released per unit volume of fuel during complete combustion, calculated by multiplying mass energy density by density ($MJ\,L^{-1}$ or $MJ\,dm^{-3}$).

Aliquot

A measured sub-volume of a liquid sample taken for analysis or dilution using a volumetric pipette.

Mass Concentration

The mass of a dissolved solute present per unit volume of solution, expressed in units of $g\,L^{-1}$ or $g\,dm^{-3}$.

Dilution Factor

The ratio of the final diluted volume to the initial aliquot volume (such as $250.0\,mL / 10.00\,mL = 25.00$), used to calculate original concentration from a diluted concentration.

Hydration Energy

The heat released when gaseous ions interact with water molecules during dissolution; when crystal lattice separation energy exceeds hydration energy, dissolution is overall endothermic.