Thermochemistry and Gases

Vocabulary flashcards covering thermochemistry, gas laws, intermolecular forces, and phase changes. Terms and definitions are based on lecture notes.

Thermodynamics

The study of energy and its interconversions.

System

The area or location under study.

Surroundings

Area or location outside the system.

Universe

System + surroundings.

Endothermic

Heat transfers from surroundings to the system.

Exothermic

Heat transfers from the system to the surroundings.

State Function

DE and DH, these do not depend on the path taken.

Work (w)

Transfer of energy by motion (macroscopic objects).

Heat (q)

Transfer of thermal energy (vibration of atoms/molecules).

Heat

The exchange of thermal energy between a system and it’s surroundings.

Temperature

The measure of thermal energy in a system.

Specific Heat Capacity

Measure of a substance’s intrinsic ability to absorb heat; the amount of heat energy required to raise the temperature of one gram of a substance 1 °C. Units J/(g∙°C)

Pressure-Volume Work

PV work is work caused by a volume change against an external pressure.

∆Erxn = qrxn

Change in energy equals heat of reaction.

Enthalpy (DH) “Heat of Reaction”

The amount of heat absorbed or released by a reaction at constant pressure.

Hess's Law

The change in enthalpy for a stepwise process is the sum of the enthalpy changes of the steps.

Bond Energy

It always takes energy to break one of these.

Standard State

Conditions for gases @ 1 atm, solutions @ 1 M concentration, and Temp @ 25oC.

DE

Internal energy, all of the energy present in a system.

DH

Heat of reaction that takes into account only the heat released (q) during a chemical reaction disregards work (w).

Ideal gas

These gas molecules have no volume and no intermolecular interactions; a point in geometry is a location with no width, length, and depth.

Gas Pressure

Gas pressure is caused by molecules colliding with the container.

STP

Standard Temp = 0o C (273 K) & Standard Pressure = 1 atm.

Partial pressure

The amount of pressure exerted by each gas in a mixture.

Diffusion

Diffusion is the process of gases expanding to fill a space or container.

Effusion

Effusion is the process by which a gas escapes a container through a tiny hole.

Condensed Phases Attractiions

Liquids and solids, attractive force between molecules (intermolecular) these are Hydrogen Bonds, Dipole-dipole, and London Dispersion Forces.

Dipole-Dipole Interactions

Polar molecules have positive and negative sides and attracted to one another.

Hydrogen Bond Donor

Naked proton need H bonded directly to F, O, N.

Hydrogen Bond Acceptor

Lone pair of electrons.

London Dispersion Forces

A weak force present in every molecule; Individual (single) interactions are very weak, but there may be several in a large molecule.

Ion-Dipole Attraction

Ions from an ionic compound attracted to the dipole of polar molecules.

Boiling Point

Boiling occurs when the vapor pressure of a liquid equals the external pressure.

Supercritical Fluid

A liquid is heated in a sealed container, more vapor collects, causing the pressure inside the container to rise; have properties of both gas and liquid states.

Sublimation

solid becoming a gas.

Deposition

Gas becoming a solid

Heat of Fusion

Amount of heat needed to change the phase from solid to liquid (melt the solid) at the melting point.

Solid

Rigid shape, molecules not moving.

Liquid

Takes on shape of container, molecules able to move past one another (flows).

Gas

Fills the entire container (shape and volume) lots of empty space (compressible).

Crystalline lattice

Specific & regular arrangement of the atoms.

Unit cell

Simplest collection of atoms that can be repeated to produce the lattice.