Thermochemistry - General Chemistry (Chapter 6)

Comprehensive vocabulary review flashcards covering Chapter 6: Thermochemistry, including energy forms, the First Law of Thermodynamics, enthalpy, thermochemical equations, calorimetry, and Hess's Law.

Energy

The capacity to move matter.

Radiant Energy

A form of energy consisting of electromagnetic radiation.

Thermal Energy

The form of energy associated with the random motion of a molecule or atom.

Chemical Energy

Energy stored within the structural limits of a molecule or atom.

Kinetic Energy ($E_k$)

The energy associated with an object by virtue of its motion, calculated as $E_k = \frac{1}{2}mv^2$.

Potential Energy ($E_p$)

The energy an object has by virtue of its position in a field of force, calculated for a gravitational field as $E_p = mgh$.

Joule ($\text{J}$)

The SI unit of energy, equivalent to $1\,kg \cdot m^2/s^2$.

Calorie ($\text{cal}$)

A unit of energy defined as the amount of energy needed to raise the temperature of one gram of water by $1\,^\circ\text{C}$, exactly equal to $4.184\,\text{J}$.

Internal Energy ($U$)

The sum of the kinetic and potential energies of the particles making up a substance.

State Function

A property or function that depends only on the initial and final states of the system, not on how the change was accomplished.

First Law of Thermodynamics

The law of conservation of energy applied to a thermodynamic system, relating internal energy change to heat and work by the equation $\Delta U = q + w$.

Open, Closed, and Isolated Systems

Three classifications of thermodynamic systems: an open system can exchange both energy and matter with its surroundings; a closed system can exchange energy but not matter; and an isolated system exchanges neither energy nor matter.

Thermodynamics

The science of the relationship between heat and other forms of energy.

System

The specific part of the world in which there is special interest (such as a reaction vessel, engine, electrochemical cell, or biological cell).

Surroundings

The region outside the thermodynamic system where measurements and observations are made.

Exothermic Reaction

A reaction or process that results in the evolution of heat where energy flows out of the system into the surroundings ($q < 0$ and $\Delta H < 0$).

Endothermic Reaction

A reaction or process that results in the absorption of energy from the surroundings where heat flows into the system ($q > 0$ and $\Delta H > 0$).

Thermochemical Equation

A balanced molecular equation that includes phase labels and writes the enthalpy of reaction directly after the equation.

Heat ($q$)

A transfer of energy between two objects caused by a difference in temperature.

Work ($w$)

An energy transfer associated with mechanical movement; work done on the system by the surroundings is positive ($w > 0$), while work done by the system on the surroundings is negative ($w < 0$).

Calorimeter

A device used experimentally to determine the heat associated with a chemical reaction.

Calorimetry

The science of measuring heat based on observing temperature changes when a body absorbs or discharges energy as heat.

Heat Capacity ($C$)

The amount of energy required to raise the temperature of a given system by $1\,^\circ\text{C}$, expressed as $C = \frac{q}{\Delta T}$ in units of $\text{J}/^\circ\text{C}$.

Specific Heat Capacity ($s$)

The energy required to raise the temperature of one gram of a substance by one degree Celsius, expressed in units of $\text{J}/(g \cdot ^\circ\text{C})$.

Molar Heat Capacity

The energy required to raise the temperature of one mole of a substance by one degree Celsius, expressed in units of $\text{J}/(mol \cdot ^\circ\text{C})$.

Enthalpy ($H$)

A thermodynamic property defined as $H = E + PV$, whose change at constant pressure is equal to the heat flow ($\Delta H = q_p$).

Standard State

The standard thermodynamic conditions chosen for substances at a pressure of $1\,\text{atm}$ and a temperature of $25\,^\circ\text{C}$.

Standard Enthalpy of Formation ($\Delta H_f^\circ$)

The enthalpy change for the formation of one mole of a substance in its standard state from its elements in their standard states (defined as zero for an element in its standard state).

Hess's Law

The principle stating that in going from a particular set of reactants to a particular set of products, the change in enthalpy is the same whether the reaction takes place in one step or in a series of steps.