Limiting Reagents, Enthalpy, and Reaction Dynamics

These flashcards cover key vocabulary from the lecture transcript regarding limiting reagents, percent yield, collision theory, thermodynamics, and changes in enthalpy during phase transitions.

Limiting reagent

The reactant in a chemical reaction that determines the amount of product that can be formed and is used up first.

Excess reagent

Any reactant that is not used up in a chemical reaction.

Theoretical yield

The calculated maximum amount of product that can be formed from a reaction based on a balanced chemical equation.

Actual yield

The amount of product actually made during a real reaction, which can be measured in a lab.

Percent yield

The ratio of the actual yield to the theoretical yield expressed as a percent, calculated as $\frac{\text{Actual yield}}{\text{Theoretical yield}} \times 100$.

Collision theory

States that bonds are broken and or formed when reacting particles collide with enough energy and with the correct orientation.

Activated complex

An unstable cluster of atoms that exists during the transition from reactants to products during a chemical reaction.

System

The specific part of the universe on which you focus your attention.

Surroundings

Everything else in the universe outside of the system.

Heat

Energy that moves from one object to another due to a temperature difference, always flowing from warmer objects to cooler objects.

Enthalpy

A quantity used by chemists to account for heat flow in systems at constant pressure, represented by the symbol $\Delta H$.

Bond enthalpy

The amount of energy required to break the bonds of one mole of a substance.

Electrolysis

An endothermic process involving the electrically driven decomposition of water into hydrogen gas and oxygen gas.

Activation energy

The minimum energy that colliding particles must have in order to react; it serves as a barrier reactants must overcome before products can form.

Exothermic reaction

A reaction where energy is released, often shown as a down arrow in an enthalpy diagram or written as a product in a thermochemical equation.

Endothermic reaction

A reaction where energy is absorbed, often shown as an up arrow in an enthalpy diagram or written as a reactant in a thermochemical equation.

Law of heat summation

Also known as Hess's Law, it states that if you add two or more thermochemical equations to give an overall equation, you can also add the enthalpies of reaction to find the overall enthalpy change.

Standard state

The stable form of a substance at a temperature of $25^{\circ}C$ and a pressure of $100\,kPa$.

Standard enthalpy of formation

The change in enthalpy when one mole of a compound is formed from its elements with all substances in their standard states; it is set at zero for free elements.

Molar enthalpy of solution

The enthalpy change caused by the dissolution of one mole of a substance.

Molar enthalpy of fusion

The heat absorbed by one mole of a solid substance as it melts to a liquid at a constant temperature.

Molar enthalpy of solidification

The heat lost when one mole of a liquid substance solidifies at a constant temperature.

Molar enthalpy of vaporization

The heat absorbed by one mole of a liquid substance as it vaporizes at a constant temperature.

Molar enthalpy of condensation

The heat lost by one mole of a gas substance as it condenses at its normal boiling point.

Evaporation

The process by which particles at the surface of a liquid gain enough energy to break free from intermolecular forces and enter the gas phase below the boiling point.