Kim P.

Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry deals with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds. Chemistry also involves understanding the properties and interactions of individual atoms and molecules for use in larger-scale applications.

In chemistry and physics, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ultimately composed of atoms, which are made up of interacting subatomic particles, and in everyday as well as scientific usage, "matter" generally includes atoms and anything made up of them, and any particles and objects that act as if they have both rest mass and volume. However it does not include massless particles such as photons, or other energy phenomena or waves such as light or sound. Matter exists in various states (known as phases) that are defined by various physical properties, such as state of matter, phase, shape, and density. The Standard Model of particle physics and the general theory of relativity describe fundamental particles and the fundamental forces acting between them that control the structure and dynamics of matter.

In physics, energy is the property that must be transferred to an object in order to perform work on, or to heat, the object. Energy is a conserved quantity; the SI unit of energy is the joule (J). Energy can be transformed, not created or destroyed. The laws of thermodynamics state that energy can be transformed from one form to another, but it is not possible to create or destroy it. The total energy of a system can be calculated by adding up all forms of energy in the system. The total energy of a system is sometimes called its "energy content". Different forms of energy can be transformed into one another, but it is not possible to create or destroy energy.

In science, a unit is a standard numerical value used to quantify a physical quantity. A unit can be defined by a fundamental physical law or empirical observation and can be expressed as a conventional value of a physical quantity or a rationalized additive constant.

In chemistry, uncertainty is the expected error in a measurement, which is the difference between the value of a measured quantity and the value of the quantity as determined by the measurement process. Uncertainty is usually expressed in terms of standard deviation. Uncertainty can be quantified in several ways: for example, by using statistical methods, or by analyzing the variance of the individual measurements. The term "uncertainty" is also used in science and engineering in a broader sense, to indicate the lack of knowledge of either the value of a quantity or even its existence.

In science, engineering, and statistics, accuracy and precision are distinct concepts. The accuracy of a measurement system is the degree of closeness of measurements of a quantity to that quantity's true value, which is a function of the inherent variability of the measurement system. The precision of a measurement system, also called reproducibility or repeatability, is the degree to which repeated measurements under unchanged conditions show the same results.