Chemistry Help and Problems
In our chemistry help section, you'll find a broad range of topics from very basic chemistry all the way through some more advanced organic chemistry topics. Browse our chemistry topics below, or contact one of our chemistry tutors for private help.
This page gives a general description of what atoms, elements, and compounds are. Details about what makes an element, or a compound, are given. Basic terminology is explored, explaining many vocabulary words that will repeat throughout the study of Chemistry.
Matter is defined as anything that has mass and takes up space. Matter exists as liquids, solids and gases. This lesson discusses the physical properties of matter, which can be observed and measured without changing the chemical makeup of the matter.
Chemical properties of matter are also observable, but that doesn't necessarily mean you can "see" the property just by looking at it. Chemical properties are often measured through chemical reactions, or changes to the element or compound in question. This lesson describes the differences between chemical and physical properties of matter.
Almost everyone has heard of teh periodic table, but do you know how to read it? This lesson gives you a brief history of the periodic table, and explains how elements are divided and grouped in the table.
Mixtures and solutions may seem to have a lot in common, but they're actually very different. A mixture exists when two (or more) substances are combined, and each substance retains its chemical identity. A solution exists when two (or more) substances are combined to make a homogen
Scientific notation is an alternative form of expressing very big or very small numbers. It is used in science to express very large measures, like the Earth's weight, or very small numbers, like the number of electrons in a mole of a substance. Read more to find out how to express numbers in scientific notation!
Read this article for a description of an atom, as well as a quick guide to atomic number, mass number, and atomic symbol. Isotopes, ions, and atomic mass are also reviewed in this lesson.
This page explains how to measure in grams, moles, and more! You will learn how to do different types of conversions and problem solving using grams and moles. This page also explains dimensional analysis.
Polyatomic ions are ions with many atoms; they contain more than one element. They are charged just like regular ions; for example, an ion looks like this: Cl-, while a polyatomic ion looks like this: ClO3-. While the chloride ion only contains one element - chlorine - the chlorate ion contains both chlorine and oxygen. Read this lesson for examples of other commonly known polyatomic ions.
This page gives a general overview of the different types of equations studied in Chemistry, including single displacement reactions, double displacement reactions, precipitation reactions, combustion reactions, acid-base reactions, and oxidation/reduction reactions (also known as redox reactions).
Oxidation reactions and reduction reactions are complementary reactions that involve the transfer of electrons from a reductant to an oxidant. These types of reactions always work together. Read this lesson to find out more specifics about redox reactions!
Electronegativity is a property of atoms that has to do with the tendency to attract electrons from another atom to form an ionic bond. Electronegativity is measured using the Pauling scale, which was instated by Linus Pauling. Read this lesson to find out all about electronegativity!
All reactions can be classified as endothermic (storing energy) or exothermic (releasing energy). This lesson reviews the ways in which reactions store and give off energy, including items like heat, light, and mechanical energy. Once you've read this lesson, test yourself with a quick practice quiz to review the endothermic and exothermic concepts.
Due to the law of conservation of energy, which says that energy cannot be created or destroyed, chemical equations must be balanced. Read this lesson for more information on how to balance chemical equations
LeChatelier's principle says that when a change is introduced to a system in equilibrium, the equilibrium shifts in the direction that relieves the change. The three main things that cause the equilibrium to change are temperature, pressure, and concentration (of the reactants or products). Read more to learn about how equilibrium stabilizes after a change in pressure, temperature, or concentration!
Hydrolysis occurs when one adds water to a compound, which causes the compound to break apart into a cation and an anion. Then, water can bond chemically with the substance, changing its chemical form.These reactions often take place when ionic compounds dissolve in water. Read on to learn more about the process of hydrolysis!
When a reaction is in a state of dynamic equilibrium, the reaction is reversible. This means that, to maintain equilibrium, the products break apart to form the reactants. Read this lesson for more information on dynamic equilibrium!
A titration is a controlled addition of one substance into another. In an acid-base titration, the observer typically adds a base with a certain concentration to an acid of an unknown concentration (or vice versa). The observer places an indicator in the flask, so that he/she knows when the reaction has reached an endpoint. Read on to learn more about acid-base titrations!
Buffer solutions are used to prevent changes in pH in solutions. For the most part, buffer solutions are made by mixing a weak base with its conjugate acid, or a weak acid with its conjugate base. Read on to find out more about how buffer solutions behave and are used!
After studying the different types of equations, you’ll run into problems that don’t work because you don’t have the right ratio of one chemical to another. Stoichiometry, also known as balancing equations, helps you determine the right amount of each reactant in order to produce the desired product(s)!
Enthalpy is a state function that is measured in kilojoules per mole. Enthalpy is abbreviated as H in the Gibbs free energy equation: G = H - TS. Enthalpy can help an observer discern whether a reaction is endothermic or exothermic based on the enthalpy having a positive or negative value. Read on to find out more about enthalpy!
Like enthalpy, entropy is also a state function that is defined as ΔS, or Sf - Si. It is a spontaneous reaction that occurs naturally. Entropy measures the disorder of a system. Read this lesson to learn more about entropy!
Mass spectrometry is used to experimentally determine the molecular weight of a sample by ionizing a molecule and passing it through electrical and magnetic fields. The observer would then note how the ionized compound responds, which correlates with the molecular weight in a quantifiable way. Read on to learn more about the intricate process of mass spectrometry!
This page starts with the simpler gas laws, Boyle’s Law and Charles’s Law, Gay-Lussac's Law, and Avogadro's Law, and moves on to explaining, and implementing, the ideal gas law (also known as the ideal gas equation). Brief discussions of STP and the ideal gas constant, R, as well as the ideal gas law, PV=nRT, are also included.
Graham's law states that the effusion of a gas is inversely proportional to the square root of the molar mass of its particles. In an equation, it is described as Rate1/Rate2 = √M2/M1. Read on for more information on how to use Graham's law in a practical way.
Hess's law is much like solving a puzzle using the change in entropy of a reaction. The result is that one can tell the change in energy (in kJ/mol) of a reaction. Hess's law requires a balanced equation with proper coefficients. Read on for more advice on implementing Hess's law!
The Born-Haber cycle is a series of chemical processes that are used to calculate the lattice energy of ionic solids. The Born-Haber cycle can be thought of as a special case of Hess's law. Read on for a definition of lattice energy as well as examples of how the Born-Haber cycle is used to calculate lattice energy.
This page identifies different types of bonds, including covalent, polar covalent, ionic, and hydrogen. It explains how to draw compound structures by counting electrons and placing bonds accordingly. The Octet and Duet rules are also explained here.
This page details how electrons are arranged in an atom, including information about the orbitals (s, p, d, and f) and how to easily tell which orbital an electron is in. You’ll also learn about the diagonal rule and electron spin.
Electron delocalization can be really confusing! In order to understand this concept, one must learn about resonance, bonding, and aromaticity. Read on for more information about electron delocalization!
The Aufbau principle describes how electrons fill energy levels in an atom. In order to write the electron configuration of an atom, one must know how the subshells fill. Using the diagonal rule will certainly help with this process. Read on for more information about the Aufbau principle.
Electron Dot Diagrams, Lewis Dot Symbols, and Lewis Structures are all defined and explained. VSEPR, Valence Shell Electron Pair Repulsion, and Molecular Geometry are also explained in order to determine molecular shape.
Hybridization occurs when two atomic orbitals combine to form one hybrid orbital. One of the more common types of hybridization is sp3 hybridization, which is described in detail in this lesson. Read on for more detailed information on the intricacies of electron orbitals.
Electrolysis occurs in electrolytic cells when an electrical current causes a nonspontaneous oxidation-reduction reaction. This lesson describes how electrolysis is used, including extracting pure metals from the Earth's crust. Read on for more information on the process of electrolysis!
Voltaic cells use chemical energy to do electrical work. A redox reaction occurs, and the electrons are forced through an electrical circuit. Read on to find out the specifics on how voltaic cells power electrical processes!
The study of nuclear reactions is called radiation chemistry. A nuclear reaction involves the nucleus of an atom. These types of processes were first discovered by Marie Curie in the late 1800s. Read on for more details about radiation chemistry!
Introduces carbon structures and interactions between molecules. Basic vocabulary and ideas are introduced concerning alcohols and hydrocarbons. Combustion of a hydrocarbon is also discussed briefly.
Alkanes and alkenes are both hydrocarbons that follow the standard nomenclature procedures. Learn whether alkanes and alkenes are saturated or unsaturated, which is more reactive, and how to name a compound by looking at its structure in this lesson.
When aromatic compounds undergo reactions with electrophiles, a substitution reaction occurs. This reaction is known as an electrophilic aromatic substitution (EArS or EAS) reaction. Read on for an in-depth description of how these reactions occur!
Halogenoalkanes are exciting because, compared to alkanes, they are very highly reactive when paired with nucleophiles or bases. Halogenoalkanes are also SP3 hybridized. Read this lesson to find out more information on halogenoalkanes!
A carbonyl condensation reaction occurs between two carbonyl partners and involve nucleophilic addition and α substitution. This lesson also covers aldol condensation as well as the Robinson annulation reaction. Read on for more details about these chemical processes.
An elimination reaction occurs when a starting product breaks down into two new products that contain all the atoms of the original reactant. There are two types: E1 and E2. Read this lesson for more information about elimination reactions.
Nucleophilic substitution reactions occur when a nucleophile interacts with an electrophile. Read this lesson for a step by step explanation of what happens during a nucleophilic substitution reaction.
This lesson also covers nucleophilic substitution including the SN1 and SN2 mechanisms. Effects on kinetic rate, alkyl group, and more are discussed in this lesson.
Because many students cannot and do not draw organic structures correctly, one of our most prominent chemistry tutors took the time to explain how to draw cyclohexane rings in great detail. She even shows more than one way to get a perfect drawing of this ring. Read the lesson to find out how to draw these rings correctly!
Stereoisomers are a category of isomers. Learn about the different categories of isomers in this lesson, and how you will study stereoisomers in chemistry and biochemistry.
This page contains a ton of information that is largely relevant to the study of chemistry, including the solubility rules, a list of common conversion factors, equations, and an ion list. Please see other pages for explanations of these terms and equations; this is purely for you to go back and quickly use as a reference guide after you understand the basic principles.
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