CHEMISTRY COMMUNITY

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You would balance all elements except for hydrogen and oxygen, then balance the oxygen by adding H2O. You would then balance the hydrogen using H+. Finally, balance the charge in the half-reaction using electrons.

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Enzymes act as catalysts. They do not get consumed in the chemical reactions that they accelerate. They speed up reactions by lowering the activation energy.

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A reaction profile shows how the energy of the reactants and products changes during a reaction.

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In a chemical reaction or mechanism, an intermediate is any reacting species that is no longer starting material or reactant, and has not yet become product.

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It means that the rate does not vary with the increase or decrease in the concentration of the reactants.

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Electromotive force (EMF) is equal to the terminal potential difference when no current flows.

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Standard reduction potentials are measured with relativity to hydrogen which has a potential of zero. A standard reduction potential is measured using a galvanic cell which contains a SHE on one side and an unknown chemical half cell on the other side. A negative value of cell potential represents a...

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The reducing agent is stronger when it has a more negative reduction potential and weaker when it has a more positive reduction potential.

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The best reducing agents are located at the bottom left of the periodic table (low electronegativity) and the best oxidizing agents are located at the top right of the periodic table (high electronegativity), excluding noble gases.

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If the E cell values of the reaction is negative, then the reaction is not spontaneous and therefore the reverse reaction is occurring.

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A salt bridge is used to connect the oxidation and reduction half-cells of a galvanic cell. It keeps both solutions at a neutral state, so the electron flow will be able to continue for a more extended time period.

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By changing the concentration of one solution, you increase the number of cations and anions in the cell. This will increase the voltage potential of the cell because you are putting the system further out of equilibrium.

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An electrode is a solid electric conductor that carries electric current into non-metallic solids, or liquids, or gases. An electrode has to be a good electrical conductor so that is why it is usually a metal.

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Larger molecules have more atoms and so they have more ways in which they can be arranged. Entropy measures disorder so larger molecules have larger entropy.

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Exergonic reactions are spontaneous reactions because they can occur without the addition of energy.

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Yes! Not all irreversible reactions are isothermal, but all reversible reactions are isothermal.

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Adding water to concentration cells would alter the molarity of the reactants.

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An adiabatic process occurs without transferring heat or mass between the system and its surroundings.

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The second law of thermodynamics says that when energy changes from one form to another form, or matter moves freely, entropy (disorder) in a closed system increases.

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The particles of an ideal gas are assumed to occupy no volume and experience no inter-particle attractions. The particles of a real gas do have finite volumes and do attract one another.

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When we consider a refrigerator or heat pump as a system, we have to supply work as input. So it's an example of work on the system.

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When ΔH is negative and ΔS is positive, the sign of ΔG will always be negative, and the reaction will be spontaneous at all temperatures

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In a irreversible process, the work done by volume expansion goes against an external pressure that doesn't change. In an irreversible process, if the system is pushing against a piston, the system can't just reset to its original position.

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Enthalpy is a thermodynamic property of a system. It is the sum of the internal energy added to the product of the pressure and volume of the system.

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Residual entropy is the entropy that remains after molecules stop moving (due to the orientation of the atoms of the molecule) at 0 degrees kelvin.

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V1 is the initial volume and V2 is the final volume.

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An open system can exchange matter and energy. A closed system can exchange energy like heat but not matter. An isolated system cannot exchange energy or matter.

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The equation applies to reversible systems.

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Enthalpy is a measure of heat content of the system, whereas entropy is the measure of change in enthalpy/temperature.

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Condensation is an exothermic reaction because the water is changing from the gas phase, or water vapor in the air, into the liquid phase.For condensation the molecules are giving up their heat energy. When molecules give up heat energy, it is exothermic.

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HClO3 is a strong acid due to the multiple oxygens bonded to the central atom.

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The addition of a non-reactive gas does not change the partial pressures of the other gases in the container.

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During a phase change, matter changes from one phase to another, either through the addition of energy by heat and the transition to a more energetic state, or from the removal of energy by heat and the transition to a less energetic state. Some phase changes include melting, vaporization, sublimati...

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A perfect system guarantees that the heat gained/lost by the system will be equal to the negative heat lost/gained by the surroundings. The heat given off by the reaction equal to heat absorbed by the surroundings.

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That is the correct formula for calculating percent ionization!

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Water is omitted from the equilibrium expression only if it is a solvent in that reaction because it is a pure liquid. We can't increase the concentration of a pure liquid or pure solid.

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Temperature tells you the ability of heat to transfer for a given scenario. Enthalpy tells you exactly how much heat energy is contained within an object. It takes more heat energy to go from water to steam than it does to go from water to boiling water. Since it takes more heat energy to go through...

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Heat is a transfer of energy due to a temperature difference where as enthalpy is the change in amount of heat in a system at constant pressure.

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Autoprotolysis is a transfer reaction between two identical molecules one acting as a Brønsted acid and the other as a Brønsted base.

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An endothermic process has a positive delta H because the system is gaining heat. An exothermic process has a negative delta H because the system is losing heat.

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Kw is the autoionization constant and Ka is the acid dissociation constant. Kb is the base ionization constant. Kw will always be 10^-14
b

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A species that has the potential to act both as an acid and as a base is amphoteric. The water molecule has hydrogen atoms and could act as an acid in a reaction. Since water has the potential to act both as an acid and as a base, water is amphoteric.

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A reaction is exothermic when the enthalpy change is negative and heat is released due to the fact that there is less energy(enthalpy) within the products than the reactants. A reaction is endothermic when the enthalpy change is positive and heat is absorbed because the products now have more energy...

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Compounds are usually labeled as (s) for solid or (l) for liquid

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You can tell if a substance is an acid or a base by counting the hydrogens on each substance before and after the reaction. If the number of hydrogens has decreased that substance is the acid (donates hydrogen ions). If the number of hydrogens has increased that substance is the base (accepts hydrog...

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Your first step should be to determine which positive value aligns with the other values within the problem. The positive number that is larger than the initial conditions should be disregarded.

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Pure solids or liquids are excluded from the equilibrium expression because their effective concentrations stay constant throughout the reaction.

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Ideal gases abide by all gas laws regardless of the pressure of temperature. Ideal gases occupy no volume. Real gases occupy small volumes. Ideal gas particles exert no attractive forces and their collisions are elastic. Real gases exert small attractive forces. The pressure of an ideal gas is great...

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Solvents are indicated by (l) and are not utilized when calculating the equilibrium constant.

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This statement is true because Kc, the equilibrium constant, represents the ratio of products to reactants when the reaction is at equilibrium. A higher concentration of reactants results in a higher concentration of products to maintain the ratio.

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A terminal atom is essentially any atom that is not a central atom. Terminal atoms surround and connect to the central atom.

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A conjugate acid contains one more H atom and one more + charge than the base that formed it. A conjugate base contains one less H atom and one more - charge than the acid that formed it. All acids and bases have conjugate bases.

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The transition metal is the central atom in a coordination compound.

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Chelates, any of a class of coordination or complex compounds consisting of a central metal atom attached to a large molecule, called a ligand, in a cyclic or ring structure.

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Electronegativity is a measure of the attraction of an atom for bonding electrons in molecules compared to that of other atoms. Large electronegativity values represent a stronger attraction for electrons than small electronegativity values. Electronegativities increase from left to right across the...

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Resonance structures should have the same number of electrons, do not add or subtract any electrons. (check the number of electrons by simply counting them). Resonance structures must also have the same amount of lone pairs. The location is the changing factor.

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Electron Geometry is the shape the electrons take around the central atom. These electrons can be in either a chemical bond or in lone pairs. Molecular geometry is described on the basis of bonding electron pairs NOT the number of electron pairs.

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Molecules joined by a pi bond cannot rotate about that bond without breaking the pi bond, because rotation involves destroying the parallel orientation of the p orbitals.

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A polydentate ligand can be recognized by having more than 2 lewis base sites, including multiple lone pair donating sites used to bond to a central atom or ion.

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A bond pair that travels between two atoms is considered to be localized. A bond pair that moves between two different pairs of atoms is considered delocalized. Delocalized bonds can be identified by checking the electron locations in two different resonance forms; if the pair changes location and f...

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Liquids that flow slowly have high viscosities and liquids that flow readily have low viscosities. Liquids whose molecules are polar are usually more viscous than similar nonpolar substances. Liquids with long molecules are invariably very viscous. The viscosity of a liquid decreases as temperature ...

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Ionic liquids are salts with an organic cation and either an organic or inorganic anion. They exist as liquid at temperatures below 100 degrees Celsius. They have irregular structures, which delocalize their charges.

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Bond order is defined by the number of chemical bonds between a pair of atoms and indicates the stability of a bond. In a covalent bond between two atoms, a single bond has a bond order of one, a double bond has a bond order of two, and so on. Bond order and length are inversely proportional. When b...

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Viscosity increases with stronger intermolecular forces caused by increase in the molecular weight, and decreases with higher temperature. Surface tension increases as the intermolecular forces increase.

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A sigma bond (σ bond) is a bond formed by the overlap of orbitals end-to-end. The electron density is concentrated between the nuclei of the bonding atoms. A pi bond (π bond) is a bond formed by the overlap of orbitals side-by-side. The electron density concentrated above and below the plane of the ...

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Hydrogen bonding occurs only in molecules where hydrogen is covalently bonded to one of three elements: fluorine, oxygen, or nitrogen. These elements are so electronegative that they take majority of the electron density in the covalent bond with hydrogen, leaving the H atom very electron-deficient....

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A shell contains one or more subshells. A subshell contains one or more orbitals. An orbital can contain up to 2 electrons. Shells are assigned a principle quantum number, n (n = 1, 2, 3, ...). Subshells are labeled differently as s, p, d, f. The orbitals are the specific region of space where the e...

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Elements in group 1 have one valence electron; elements in group 2 have two valence electrons; elements in group 13 have three valence electrons; elements in group 14 have four valence electrons; and so forth up to group 18. elements in group 18 have eight valence electrons, except for helium, which...

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All molecules experience London dispersion forces because each molecule have moments where their electrons move to one side of the atom. The atom becomes slightly negative and slightly positive on either sides, which attracts another atom.

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You can determine the number of orbitals you have in a particular shell by using the principal quantum number,
n. The number of orbitals can be found using n^2. So n=7 will contain 49 orbitals.

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The textbook mentions that for most Group 13 elements like B and Al, the atoms don't need a complete octet in the Lewis structure. They only need about 6 electrons.

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NO2- is not a radical because it does not have any unpaired valence electrons. NO2 is a nitrogen-centered radical.

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Delocalized electrons are electrons in a molecule, ion or solid metal that are not associated with a single atom or a covalent bond. Electrons that can move around are delocalized – they can be placed on one atom but can also be shared between that and the neighboring atom, i.e. can participate in r...

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If they have less than three valence electrons, it is easier to lose them and become a positively charged ion. If they have more than four valence electrons, it is easier to gain electrons and become negatively charged.

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An element from Period 3 and below is able to expand octet by making use of its low lying d-subshell for bonding.

This means only Period 2 elements such as C, N, O and F cannot expand octet and have to obey octet rule.

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The formal charge equation compares the number of valence electrons in an isolated neutral atom with the number of valence electrons around the atom in the molecule. Knowing the formal charge on a particular atom in a structure is an important part of keeping track of the electrons and is important ...

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Isoelectronic refers to two atoms, ions, or molecules that have the same electronic structure and the same number of valence electrons. Isoelectronic means "equal charge". They typically display similar chemical properties. Atoms or ions with the same electronic configurations are said to ...

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A delocalized electron is an electron in an atom, ion, or molecule not associated with any single atom or a single covalent bond. You can identify delocalized electrons by looking at the ring structure. Delocalized electrons are indicated by drawing a circle rather than single and double bonds. Anot...

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Electrons do behave like they're "spinning" in experiments but electrons do not actually spin. The electron does have angular momentum. An object that is spinning on an axis has an angular momentum, which is determined by how the mass of the object is distributed about the axis, and how fa...

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Bond length is the distance between two nuclei of atoms that are covalently bonded together and it ranges from 0.1 to 0.2 nm. Bond length depends on the bond order or the number of bonded electrons of two atoms. The higher the bond order, the shorter the bond length will be because of the positively...

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If a photon has an energy at least as big as the work function, the photon energy can be transferred to the electron and the electron will have enough energy to escape from the metal. But a photon with an energy less than the work function will never be able to eject electrons.

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The ionic radius is a measure of an atom's ion in a crystal lattice. It is half the distance between two ions that barely touch each other. Ionic radius increases as you move from top to bottom on the periodic table and decreases as you move left to right on the periodic table.

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Yes, the work function can be a negative value. The negative work function tells you how much work needs to be added to the bound electron, by the photon it absorbs. This can be seen in the photoelectric effect.

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An eV is an electron volt, which is the energy acquired by an electron accelerating through a potential difference of one volt. One electron volt is equal to 1.602176565 x 10^-19 J (joules) and one joule is equivalent to 6.241509 x 10^18 electron volts.

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Electron affinity is the energy change when a neutral atom attracts an electron to become a negative ion. Electronegativity is an atom's ability to draw bonding electrons to itself.

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Large objects like a car fall under classical mechanics, which means you can not observe wave-like properties. Objects with small masses can be observed to have wave-like properties. Anyhting less than 10^-15 m can not be measured either.

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Frequency is related to photon's energy where E = hν , E is energy, h is Planck's constant and ν is frequency. In particle nature, intensity is related to number of photons in the radiation. Intensity is power per unit area and power is energy per time.

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The electron emits one photon, however, the larger the transition between energy levels, the more energy is absorbed/emitted. Higher frequency photons means larger energy transitions. As an example, when an electron falls from the third energy level to the second energy level, it emits a photon of r...

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You should apply significant figures at the end of the problem because that way if someone were to redo the problem using your work, they would get the same answer. Using sig figs as you work through the problem will cause your answer to vary from the actual answer.

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The smallest measurable wavelength, as stated by Dr.Lavelle, is 10^-15 M because otherwise it can not be observed.

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Planck’s constant defines the amount of energy that a photon can carry, depending on the frequency of the wave in which it travels. Planck first attempted to reproduce the expression for entropy of an ideal oscillator related to the black body radiation law. The classical theory predicted that a bod...

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Electronegativity describes how the nucleus of an atom is able to attract from other atoms towards it. Hydrogen is not the most electronegative element because it readily loses an electron rather than gaining one, despite having a half-filled shell. Under certain conditions, hydrogen does form the H...

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Nitrogen has an electron affinity of approximately zero. Adding an electron nether releases nor requires a significant amount of energy. Nitrogen has a half-filled p sub-shell, which gives it extra stability. The extra stability makes it harder to add an electron. Beryllium and magnesium have a posi...

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Atoms and electrons become excited and shift to an energetically higher quantum state by putting energy into the atom. A vacancy is created in the electron shell, which can be filled again. Each quantum level can only be populated with a certain number of electrons. The energy added to the atom need...

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Light has can behave as a particle and a wave due to the photoelectric effect. According to the photoelectric effect, when light of high enough energy comes in contact with a metal surface, electrons will be emitted from the metal. Light below a certain threshold frequency will not cause any electro...

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I’ve been taught to always use the value rounded to two digits after the decimal point. A small variation will not entirely alter your answer.

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The stoichiometric coefficient is written in front of atoms, ion and molecules in a chemical reaction to balance the number of each element on the reactant and product sides of the equation. The stoichiometric coefficients can be fractions, but whole numbers are more commonly used and preferred. Thi...

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If 1 million high energy photons hit a metal surface, the maximum number of electrons that could be ejected from the metal surface would be 1 million. The number of electrons is proportional to the light intensity. The ejection of electrons depends on the wavelength of light and the wavelength deter...

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Scientists use moles to calculate the number of atoms or molecules in a certain mass of a substance. Avogadro’s number, 6.022 x 10^23 mol^-1, is an absolute number. This means that there are 6.022 x 10^23 particles (molecules, atoms, compounds, etc) in 1 mole. The mass of one mole of a substance is ...

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When UV light comes into contact with a metal surface, an emission of electrons occurs. Light can behave as a particle and wave due to this photoelectric effect. French physicist, Louis de Broglie hypothesized that all matter hold the properties of waves. His hypothesis was proven and tested through...

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