Chemistry terms starting with P

Position Isomerism Organic Chemistry Dimensionless Structural isomerism arising from a functional group occupying different positions on the same carbon skeleton.

Positive Deviation Solutions & Colligative Properties Pa Behaviour in which a solution exerts a higher vapour pressure than Raoult's law predicts. p > x p°

Positron Emission Nuclear & Radiochemistry MeV Radioactive decay in which a proton converts into a neutron, emitting a positron and a neutrino. p → n + e⁺ + ν

Pre-exponential Factor Chemical Kinetics & Catalysis Various The constant A in the Arrhenius equation, representing the frequency of appropriately oriented collisions. A = pZ

Precipitate Stoichiometry & Chemical Reactions g An insoluble solid that separates from a solution as the result of a chemical reaction.

Precipitation Reaction Stoichiometry & Chemical Reactions Dimensionless A reaction in which two solutions combine to form an insoluble solid that separates from the mixture. A⁺(aq) + B⁻(aq) → AB(s)

Precipitation Titration Analytical Chemistry & Spectroscopy mol/L A titration in which the analyte and titrant combine to form an insoluble product. Ag⁺ + Cl⁻ → AgCl(s)

Precision Foundations of Chemistry Dimensionless The closeness of repeated measurements of the same quantity to one another, regardless of their accuracy. RSD = (s / x̄) × 100

Predicting Precipitation Chemical Equilibrium Dimensionless The use of the ionic product and solubility product to decide whether a solid will form on mixing two solutions. Q_sp > Ksp → precipitate

Pressure Equilibrium Constant Chemical Equilibrium Various The equilibrium constant for a gaseous reaction expressed in terms of partial pressures. Kp = p_C^c p_D^d / p_A^a p_B^b

Primary Cell Electrochemistry & Redox V A cell in which the electrode reaction is irreversible, so it cannot be recharged.

Primary Standard Analytical Chemistry & Spectroscopy g/mol A highly pure, stable substance that can be weighed accurately and used directly to prepare a solution of known concentration.

Primary Structure Biochemistry & Polymer Chemistry Dimensionless The linear sequence of amino acids in a polypeptide chain.

Primary Valence Inorganic & Coordination Chemistry Dimensionless In Werner's theory, the ionisable valence of a metal, equal to its oxidation state and satisfied by negative ions.

Principal Quantum Number Atomic Structure & Periodicity Dimensionless The quantum number n that specifies the main energy level and average distance of an electron from the nucleus. E_n = −13.6 Z² / n² eV

Product Stoichiometry & Chemical Reactions mol A substance formed as a result of a chemical reaction.

Promoter Chemical Kinetics & Catalysis Dimensionless A substance that has little catalytic activity itself but greatly increases the effectiveness of a catalyst.

Protein Biochemistry & Polymer Chemistry g/mol A large biomolecule made of one or more chains of amino acids folded into a specific three-dimensional shape.

Proton Atomic Structure & Periodicity u A positively charged subatomic particle found in the atomic nucleus, carrying a charge of +1 elementary unit. m_p = 1.6726 × 10⁻²⁷ kg

Proton Affinity Acids, Bases & Salts kJ/mol The energy released when a gaseous species accepts a proton, measuring intrinsic basicity free of solvent effects. B(g) + H⁺(g) → BH⁺(g)

Pseudo-First-Order Reaction Chemical Kinetics & Catalysis s⁻¹ A higher-order reaction that behaves as first order because one reactant is present in such large excess that its concentration is effectively constant. rate = k′[A], k′ = k[B]₀

Pure Substance Foundations of Chemistry Dimensionless Matter with a fixed chemical composition and a definite set of physical properties, comprising either a single element or a single compound.

Purity Foundations of Chemistry Dimensionless The mass fraction of the desired substance in a sample, usually expressed as a percentage of the total mass. purity % = (mass of pure substance / total mass) × 100

Pyrolysis Stoichiometry & Chemical Reactions °C The thermal decomposition of a substance at high temperature in the absence of oxygen. complex → simpler fragments (Δ, no O₂)

Terms starting with P