Energy, Enthalpy, and Thermochemistry Flashcards

Comprehensive vocabulary flashcards covering the nature of energy, thermodynamics, enthalpy, calorimetry, and energy sources based on Chapter 9 lecture notes.

Energy

The capacity to do work or to produce heat.

Law of conservation of energy

States that energy can be converted from one form to another but can be neither created nor destroyed; the energy of the universe is constant.

Potential energy

Energy due to position or composition, such as water behind a dam or the attractive and repulsive forces between nuclei and electrons.

Kinetic energy

Energy of an object due to its motion, calculated by the formula $KE = \frac{1}{2}mv^2$ where $m$ is mass and $v$ is velocity.

Heat

The transfer of energy between two objects due to a temperature difference.

Work

A force acting over a distance.

Pathway

The specific conditions that determine how an energy transfer is divided between work and heat.

State function (state property)

A property of a system that depends only on its present state and is independent of the particular pathway taken between states.

System

The part of the universe on which attention is focused, such as the reactants and products in a chemical reaction.

Surroundings

Everything else in the universe outside of the defined system.

Exothermic

A process in which energy flows out of the system as heat, characterized by stronger bonds in the products than in the reactants.

Endothermic

A process that absorbs energy from the surroundings, where heat flow is into the system.

Thermodynamics

The study of energy and its interconversions.

First law of thermodynamics

A statement that the energy of the universe is constant; also known as the law of conservation of energy.

Internal energy ($E$)

The sum of the kinetic and potential energies of all the particles in a system, where $\triangle E = q + w$.

PV work

Work associated with a change in volume of a gas, defined by the equation $w = -P\triangle V$.

Enthalpy ($H$)

A state function defined as $H = E + PV$, where at constant pressure the change in enthalpy ($\triangle H$) is equal to the energy flow as heat ($q_p$).

Molar heat capacity

The energy required to raise the temperature of 1 mole of a substance by $1 \text{ K}$.

$$C_v$$

The molar heat capacity of an ideal gas at constant volume, which for a monatomic gas is $\frac{3}{2}R$.

$$C_p$$

The molar heat capacity of an ideal gas at constant pressure, defined as $C_v + R$, which for a monatomic gas is $\frac{5}{2}R$.

Calorimetry

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

Specific heat capacity

The energy required to raise the temperature of $1 \text{ g}$ of a substance by $1^\text{o}\text{C}$, with units such as $J \text{ K}^{-1} \text{ g}^{-1}$.

Bomb calorimeter

A device used to study energy changes in reactions under conditions of constant volume, where $\triangle E = q_v$.

Hess’s law

States 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.

Standard enthalpy of formation ($\triangle H^\text{o}_f$)

The change in enthalpy that accompanies the formation of 1 mole of a compound from its elements with all substances in their standard states.

Standard state

A precisely defined reference state for a substance, such as $1 \text{ atm}$ for a gas or $1 \text{ M}$ concentration for a substance in solution.

Fossil fuels

Carbon-based energy sources such as coal, petroleum, and natural gas that originated from solar energy stored by plants through photosynthesis.

Petroleum

A thick, dark liquid composed mostly of hydrocarbons containing chains of 5 to more than 25 carbons.

Natural gas

A fossil fuel associated with petroleum deposits that consists mostly of methane ($CH_4$) but also contains ethane, propane, and butane.

Greenhouse effect

The process by which atmospheric gases like $CO_2$ and $H_2O$ absorb infrared radiation radiated from the earth's surface and radiate it back toward the earth, warming the atmosphere.

Syngas

Short for synthetic gas, a mixture of carbon monoxide and hydrogen produced from coal gasification.

Fracking

A technique known as hydraulic fracturing that involves injecting a slurry of water, sand, and chemical additives under pressure to access natural gas trapped in shale rock.