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If a chemical change is carried out at constant pressure and the only work done is caused by expansion or contraction, \(q\) for the change is called the enthalpy change with the symbol ΔH, or ΔH°298 for reactions occurring under standard state conditions. The value of ΔH for a reaction in one direction is equal in …

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Molecules that share the same chemical formula but differ in the placement (structure) of their atoms and/or chemical bonds isomers. Structural isomers (like butane and isobutene) differ in the placement of their covalent bonds: both molecules have four carbons and ten hydrogens (C4H10), but the different atom arrangement within the molecules leads to differences in their …

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Enantiomers are molecules that share the same chemical structure and chemical bonds but differ in the three-dimensional placement of atoms so that they are non-superimposable mirror images.


The unique properties of carbon make it a central part of biological molecules. Carbon binds to oxygen, hydrogen, and nitrogen covalently to form the many molecules important for cellular function. Carbon has four electrons in its outermost shell and can form four bonds. Carbon and hydrogen can form hydrocarbon chains or rings. Functional groups are …

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Monosaccharides (mono- = “one”; sacchar- = “sweet”) are simple sugars, the most common of which is glucose. In monosaccharides, the number of carbons usually ranges from three to seven. Most monosaccharide names end with the suffix -ose. If the sugar has an aldehyde group (the functional group with the structure R-CHO), it is an aldose, …

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Electron affinity

The electron affinity of an element is a measurable physical quantity, namely, the energy released or absorbed when an isolated gas-phase atom acquires an electron, measured in kJ/mol. We must be careful not to confuse electron affinity with electronegativity.

Nonrenewable energy

Some energy sources are classified as nonrenewable because they do not form or replenish in a short period of time. The four major nonrenewable energy sources are: Crude oil (petroleum) Natural gas Coal Uranium (nuclear energy) All fossil fuels are nonrenewable, but not all nonrenewable energy sources are fossil fuels; coal, crude oil, and natural …

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Renewable energy

Renewable energy is a kind of energy from sources that are naturally replenishing but flow-limited. Most of these renewable energies depend in one way or another on sunlight. They are virtually inexhaustible in duration but limited in the amount of energy that is available per unit of time. There are many forms of renewable energy …

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Scientific method

The scientific method is an investigative process for experimentation and an empirical method of knowledge acquisition. Is used to explore, to observe phenomena and to answer questions about the events of natural science. It consists of systematic observation, measurement, experiment, and the formulation of questions or hypotheses. The scientific method process typically begins with observations and …

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Linus Pauling

Linus Pauling is the only person to have received two unshared (individual) Nobel prizes: one for chemistry in 1954 for his work on the nature of chemical bonds and one for peace in 1962 for his opposition to weapons of mass destruction. He developed many of the theories and concepts that are foundational to our …

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