Enthalpy and Thermodynamics in Chemistry

These flashcards cover key concepts related to enthalpy and thermodynamics from your chemistry lecture notes.

Enthalpy

The total chemical energy inside a substance, also known as heat content.

ΔH

The symbol representing enthalpy change, where Δ indicates change and H indicates enthalpy.

Exothermic Reaction

A reaction where the products have less energy than the reactants, releasing heat energy to the surroundings.

Endothermic Reaction

A reaction where the products have more energy than the reactants, absorbing heat energy from the surroundings.

Activation Energy (E_a)

The minimum amount of energy needed for reactant molecules to collide successfully and start a reaction.

Enthalpy Level Diagram

A graphical representation showing the energy levels of reactants and products in a chemical reaction.

Reaction Profile Diagram

A diagram that includes activation energy and transition states in addition to showing enthalpy change.

Standard Conditions

Conditions under which measurements are made: temperature of 298 K and pressure of 100 kPa.

Standard Enthalpy Change (ΔH°)

Enthalpy change measured under standard conditions.

Standard Enthalpy of Atomization

The enthalpy change when one mole of gaseous atoms is formed from an element in its standard state.

Bond Enthalpy

The energy required to break one mole of bonds in a gaseous molecule, averaged over similar compounds.

Average Bond Energy

The energy needed to break one mole of bonds in a gaseous molecule, averaged over similar types of bonds.

Calorimetry

The measurement of heat changes in chemical reactions.

Specific Heat Capacity (c)

The energy needed to raise the temperature of 1 g of a substance by 1 K.

Hess's Law

The principle stating that the total enthalpy change in a chemical reaction is independent of the route taken.

Transition State

An unstable stage during a reaction where chemical bonds are partially broken and formed.

Calorimeter

An apparatus used to measure the change in heat energy of a chemical reaction.

Energy Transfer Calculation

Using the equation q = mcΔT to determine the energy transferred during a temperature change.

Thermochemistry

The study of heat changes that accompany chemical reactions.

Neutralization Reaction

A reaction between an acid and a base to form water and a salt.

Bond Breaking

An endothermic process that requires energy input from the surroundings.

Bond Formation

An exothermic process where energy is released to the surroundings.

Kinetically Controlled Reaction

A reaction in which the overall rate is determined by the activation energy of the slowest step.

Heat of Neutralization (ΔH_neut)

The enthalpy change when an acid and a base react completely in solution.

Excess Reagent

The reactant that remains after a reaction has gone to completion; it is not completely used up.

Energy Lost to Surroundings

Energy that is not transferred to the reacting substances but instead lost to the environment.

Equilibrium Constant (K)

A number that reflects the ratio of the concentrations of products to reactants at equilibrium.

Reactive Intermediate

A transient species that exists during the course of a reaction.

Endothermic vs Exothermic

Endothermic reactions absorb heat, while exothermic reactions release heat.

Molar Enthalpy

The enthalpy change per mole of substance during a phase change or chemical reaction.

Thermal Equilibrium

A state in which two bodies in thermal contact do not exchange energy.

Bond Dissociation Energy

The energy required to break a specific bond in a molecule.

Heat Capacity

The amount of heat needed to raise the temperature of an object by 1 K.

Standard State

The physical state of a substance under standard conditions; solid, liquid, or gas.

Combustion Reaction

A reaction where a substance combines with oxygen, releasing energy.

Dilute Solution

A solution that contains a small amount of solute relative to the solvent.

Calculation of ΔH

Using the formula ΔH = q/n to calculate enthalpy changes.

Energy Change Significance

A negative ΔH indicates an exothermic reaction, while a positive ΔH indicates an endothermic reaction.

Temperature Correction Graph

A graph used to analyze temperature changes during a reaction, addressing delays in reactions.

Energy Balance in Reactions

The comparison between energy released when bonds form versus energy required to break bonds.

Enthalpy Change Graph Interpretations

Understanding how changes in energy levels relate to enthalpy changes in chemical reactions.

Heat of Formation (ΔH_f)

The enthalpy change when one mole of a compound is formed from its elements in their standard states.

Calorimetry Errors

Errors due to heat losses, inaccuracies in measurements, or incomplete reactions.

Bond Polarity

A measure of the distribution of electric charge across a bond.

Stoichiometric Calculations

Using balanced equations to determine the quantities of reactants and products in reactions.

Product Stability

The degree to which the products of a reaction are energetically favorable compared to the reactants.

Limitations of Calorimetry

Challenges in accurately measuring heat changes due to environmental factors.

Molecular Structure Influence on Enthalpy

How the arrangement of atoms in a molecule affects its enthalpy properties.

Chemical Thermodynamics Principles

The laws governing energy transformations during chemical reactions.

Thermal Conductivity

A measure of how easily heat can pass through a material.

Reversible Reactions

Reactions that can proceed in both forward and backward directions under certain conditions.

Non-reversible Reactions

Reactions that proceed in one direction and cannot easily be reversed.

Chemical Equilibrium

The state when the rate of the forward reaction equals the rate of the reverse reaction.

Endothermic Process Example

The dissolution of ammonium nitrate in water, which absorbs heat.

Exothermic Process Example

The combustion of fuels, which releases heat.

Reaction Pathway Complexity

The various mechanisms and steps a reaction can undergo.