Chemistry Lab

The Boltzmann Expression

A probability equation that relates the entropy S of an idea gas to the quantity W, the number of microstates available in a system. The equation relates the entropy of a system to the number of ways the molecules of the system can be arranged in. The equation applies to all functions of the universe, and that each possible microstate is equally probable. However, the microstates of a such a system are not equally probable; high energy microstates are less probable than low energy microstates for a system kept at a fixed temperature.

Gibbs Free Energy

A thermodynamic quantity used to express the maximum work potential that can be performed in a system, at constant temperature and pressure. Heat must not transfer from external bodies, and volume must not increase. This maximum amount can only be calculated in a completely reversible process. In contrast, this is minimized when a system reaches chemical equilibrium at constant pressure and temperature. This is mathematically defined as the total enthalpy of the system, minus the product of the temperature and entropy of the system.

Positional Probability

A type of probability that depends on the number of arrangements in space that yield a particular state. This increases as phase changes occur due to increased thermal energy; as matter transforms, energy becomes more disordered meaning higher entropy as well.

Diamagnetism

All electrons are paired, and it produces its own magnetic field in the opposite direction, therefore it is being weakly repelled by the external magnetic field. Two electrons that share the same orbital have to have "spins," which can be thought of as "spin-up" and "spin-down" (similar to clockwise and counterclockwise). When the net spin of the electrons is zero, then they are thought to be diamagnetic.

Heat of Solvation

Also known as the enthalpy change of a solution, is the enthalpy change due to the dissolution of a substance into its accompanying solvent (assuming constant pressure). The energy change, which is the enthalpy change, happens through the breaking of bonds between the solvent and solute, and the intermolecular attraction between the solvent and solute. The total heat energy between the solvent and solute can either be a reaction that is exothermic or endothermic, though typically the breaking down of bonds is exothermic.

Heat of Formation

Also known as the standard enthalpy change of formation, is the change in enthalpy during the formation of one mole of a substance from its preceding elements (assuming constant pressure). The mole is standard unit of measurement to measure the particles of a substance. Based on whether heat energy is released or not as a mole of the substance is produced, the reaction can either be exothermic or endothermic.

Bond Enthalpy

Describes the amount of energy stored in the atomic bonds of a molecule. More specifically, it is the energy that needs to be added so that when a bond is broken, each atom associated with the molecule receives an electron. The higher the bond enthalpy, the higher the amount of energy that is necessary to break the bond - keeping in mind there is always an endothermic change.

Third Law of Thermodynamics

Entropy of a system approaches a constant value as the temperature of the system approaches absolute zero. Because molecules decrease in motion as thermal energy decreases, absolute zero hence leads to stopping molecule motion.

Second Law of Thermodynamics

Entropy of any isolated system always increases. Entropy is a quantity representing the unavailability of a system's thermal energy for conversion into work, often interpreted as the disorder present in the system. Entropy of a system cannot decrease, unless entropy is increased in another system.

Enthalpy

Equal to the total heat content of the system. Furthermore, it is equal to the internal energy of the system, plus the product of pressure and volume. Endothermic reactions mean the change in it is positive, while exothermic reactions correlate to a negative change in it. Additionally, at constant pressure, the change equals the energy transferred from the environment. It cannot be measured directly, for it is not a tangible property; for a change in it, there must be a change in temperature.

Spontaneity

Evolution of a system in which it releases energy and moves to a lower, more thermodynamically stable state. This is corresponded by a positive change in energy externally, while a negative change in energy internally. With completely isolated systems, spontaneity of those systems mean an increase in entropy. Chemical reactions are to be spontaneous if not driven by an outside force.

Kinetic Molecular Theory

Gases are made up of a large number of particles, that behave like spherical objects in a constant state of random motion. These particles move in straight lines until they collide with other particles, or the walls of the system. These particles are miniscule compared to the distance separating them. Most of the volume of gas is empty space. There is no force of attraction between gas particles or between the walls of the system. In other words, the assumption states that there is no potential energy in the particles, and therefore the total energy is equal to the kinetic energy. Collisions between gas particles are elastic; there is no net loss or gain in kinetic energy of the gas particles when they collide. The average kinetic energy of a system of gas particles depends only on the temperature of the gas, not its identity, etc. The amount of kinetic energy adjusts as the temperature varies.

Paramagnetism

Has one or more unpaired electrons, and it is attracted into an external magnetic field. Using a simple balance, one can judge if a substance is paramagnetic or not, by observing if the substance is pulled into the magnetic field created by two magnets. If an electron is alone in an orbital, then there is a net spin because the lone electron is not canceled out. If there is no other paired electron with the opposite spin, then the electron is thought to be paramagnetic.

Translucence

It allows light to pass through, but does not necessarily follow Snell's Law; in other words, a material that follows this allows the transport of light while a transparent medium not only allows the transport of light but allows for image formation. When light encounters a material, the interaction can occur in numerous ways. These certain interactions depend on the wavelength of the light and the material at hand. Based on the optics of the material, this can be described as "semi transparent."

The Boltzmann Distribution

It is a probability distribution dealing with the probability of particles in a system over various states. It gives the probability that a system will be in a certain state as a function of that particular state's temperature and energy within the system.

Opacity

It is neither transparent (allowing all light to pass through) nor translucent (allowing some light to pass through). These type of substances transmit no light, and therefore either reflect, scatter, or absorbs all incoming light.

Microstates

It's all about time and energy of the system of interest. It is also a specific way of how the energy is arranged in a system. For instance, if we had a system of three molecules, the energy output for the entire system could be arranged in a number of ways; whether each molecule possesses one unit of energy, or one molecule possesses all three units of energy. The greater amount of these, the greater entropy.

First Law of Thermodynamics

Known as the Law of Conservation of Energy, states that energy cannot be created nor destroyed in an isolated system. Energy can only be transferred from one system to another. Heat and work lead to change in the internal energy of the system; the change in energy of the system must correspond with change in energy of the surroundings.

Covalent Networking

Made up of atoms joined together by covalent bonds. Covalent bonds involve atoms sharing electrons. In addition, covalent solids are characterized as being very hard, with high melting points and low levels of conductivity.

Ionic

Made up of positive and negative ions held together by electrostatic attractions. Ions are atoms where the electron amounts are not equal to the proton amounts, which means the substance has an electrical charge. These solids are typically characterized by high melting points and brittleness, but are poor conductors in the solid state.

Density

Mass per unit volume of a certain object. It is a quantity usually expressed in g/mL or g/cm3.

State Functions

Measurable quantities of matter in a state of "nothingness" (i.e. mass, volume, pressure, temperature, etc.). All state functions must be path independent: meaning that the history of the substance does not matter on how you measure that particular state function. They are able to define the conditions in which a system exists before and after a chemical reaction.

Temperature

Measurement of the average kinetic energy of the system (implying the lack of heat, or heat thereof).

Heat Flow

Occurs when two or more objects of differing temperatures are brought together. Heat energy is always transferred from the higher temperature to the lower temperature. This continue until thermal equilibrium is reached (when the two objects reach the same temperature).

Calorimetry

Process of measuring the heat of chemical reactions or physical changes, as well as heat capacity. All calorimetric techniques are based on fact that heat can undergo exothermic/endothermic processes, or it is dissipated by a substance.

Extensive Properties

Properties of matter that depend on the amount of matter of the substance, not the chemical type (i.e. mass and volume).

Intensive Properties

Properties of matter that depend on the type of matter of the substance, not the amount (i.e. color, texture, temperature, etc.).

Specific Gravity

Ratio of the density of an substance, to the density of some other substance (namely water). The densities are both obtained by weighing in air. The masses of the substances are different, but the volumes are the same. Temperature and pressure must be specified for both substances.

Entropy

Represents the unavailability of a system's thermal energy for conversion into work, often interpreted as the disorder present in the system. It can also be interpreted as the number of states a system can take. The dispersal of energy from warmer to cooler areas always results in a net increase in entropy. Thermal energy increases this, as molecules move in a more vivid motion, thus leading to more configurations.

Hess's Law

States that regardless of the multiple stages in a chemical reaction, the total enthalpy change for the chemical reaction is a sum of all enthalpy changes.

Spectroscopy

Study of interaction between matter and electromagnetic radiation. It is measured by the spectra production when matter interacts with electromagnetic emissions/radiation. Data of this study is typically presented with an emission spectrum, which is a plot of response of wavelength or frequency.

Photoelectron Spectroscopy

The energy measurement of electrons emitted from matter due to the photoelectric effect: the fact that electrons are emitted when light is shone onto a substance. This process is done by bombarding samples with high radiation, to measure the binding energy released by the escaping electrons. The lowest binding energies correlate to valence electrons (electrons associated with atoms to create bonds), while the highest binding energies correlate to core electrons (electrons that cannot participate in bonding).

Internal Energy

The energy present within the system, excluding the kinetic energy of the moving system as a whole, and the potential energy of the whole system. Energy is accounted for by gaining and losing in the internal state of the system.

Standard Entropy of Formation

The formation of entropy from change in substance. Similar to increases and decreases in entropy, factor contributing to the formation of entropy is whether the system is isolated, molecular structure, and the type of chemical reaction.

Chemical Equilibrium

This involves that the concentrations of the reactants and products do not change over time. Most importantly, the ratio of the reactants to the products is constant at equilibrium. This means that if the total Gibbs Free Energy of a mixture of reactants and products goes through a minimum value as the composition changes, then all net change will cease; the reaction system will be in a state of chemical equilibrium. The equilibrium constant, K, expresses the relationship between products and reactants of a reaction at equilibrium with respect to a specific unit. If K=1, where reactants are equal to products, the Gibbs Free Energy will be zero. If K>1, then the Gibbs Free Energy will be negative (spontaneous). If K<1, then Gibbs Free Energy is positive, which is an endothermic reaction.

Cell Potential

This the way in which we can measure how much voltage exists between the two half cells of a battery. It involves multiple electro factors in order to calculate this quantity.

Reversibility

Those that when the reactants form the products, they react together to again form the initial reactants. The law of conservation of mass must still apply, so the atomic elements will remain intact, though they may be compounded to form different chemicals.

Work

quantity of energy transferred from a system to another system (or the surroundings), that is accounted for by external forces (i.e. electromagnetic, gravitational, pressure, etc.). It is measured in joules (J), and it disregards the transfer of entropy.